Development and application of a 2-electron reduced density matrix approach to electron transport via molecular junctions

NASA Astrophysics Data System (ADS)

Hoy, Erik P.; Mazziotti, David A.; Seideman, Tamar

2017-11-01

Can an electronic device be constructed using only a single molecule? Since this question was first asked by Aviram and Ratner in the 1970s [Chem. Phys. Lett. 29, 277 (1974)], the field of molecular electronics has exploded with significant experimental advancements in the understanding of the charge transport properties of single molecule devices. Efforts to explain the results of these experiments and identify promising new candidate molecules for molecular devices have led to the development of numerous new theoretical methods including the current standard theoretical approach for studying single molecule charge transport, i.e., the non-equilibrium Green's function formalism (NEGF). By pairing this formalism with density functional theory (DFT), a wide variety of transport problems in molecular junctions have been successfully treated. For some systems though, the conductance and current-voltage curves predicted by common DFT functionals can be several orders of magnitude above experimental results. In addition, since density functional theory relies on approximations to the exact exchange-correlation functional, the predicted transport properties can show significant variation depending on the functional chosen. As a first step to addressing this issue, the authors have replaced density functional theory in the NEGF formalism with a 2-electron reduced density matrix (2-RDM) method, creating a new approach known as the NEGF-RDM method. 2-RDM methods provide a more accurate description of electron correlation compared to density functional theory, and they have lower computational scaling compared to wavefunction based methods of similar accuracy. Additionally, 2-RDM methods are capable of capturing static electron correlation which is untreatable by existing NEGF-DFT methods. When studying dithiol alkane chains and dithiol benzene in model junctions, the authors found that the NEGF-RDM predicts conductances and currents that are 1-2 orders of magnitude below those of B3LYP and M06 DFT functionals. This suggests that the NEGF-RDM method could be a viable alternative to NEGF-DFT for molecular junction calculations.

Experimental and theoretical studies of (FT-IR, FT-Raman, UV-Visible and DFT) 4-(6-methoxynaphthalen-2-yl) butan-2-one.

PubMed

Govindasamy, P; Gunasekaran, S

2015-01-01

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 4000-50 cm(-1) and 4000-450 cm(-1) respectively for 4-(6-methoxynaphthalen-2-yl) butan-2-one (abbreviated as 4MNBO) molecule. Theoretical calculations were performed by density functional theory (DFT/B3LYP) method using 6-311G(d,p) and 6-311++G(d,p) basis sets. The difference between the observed and calculated wavenumber value of most of the fundamentals were very small. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The UV-Vis spectrum was recorded in the methanol solution. The energy, wavelength and oscillator's strength were calculated by Time Dependent Density Functional Theory (TD-DFT) and matched to the experimental findings. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Thermodynamic properties of 4MNBO at different temperature have been calculated. The molecular electrostatic potential surface (MESP) and Frontier molecular orbital's (FMO's) analysis were investigated using theoretical calculations. Copyright © 2015 Elsevier B.V. All rights reserved.

Experimental FT-IR, Laser-Raman and DFT spectroscopic analysis of 2,3,4,5,6-Pentafluoro-trans-cinnamic acid

NASA Astrophysics Data System (ADS)

Sert, Yusuf; Doğan, Hatice; Navarrete, Angélica; Somanathan, Ratnasamy; Aguirre, Gerardo; Çırak, Çağrı

2014-07-01

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized 2,3,4,5,6-Pentafluoro-trans-cinnamic acid have been investigated. The experimental FT-IR (4000-400 cm-1) and Laser-Raman spectra (4000-100 cm-1) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parameterized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with the results in the literature. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and depicted.

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

NASA Astrophysics Data System (ADS)

Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

2011-07-01

The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Structure, IR and Raman spectra of phosphotrihydrazide studied by DFT

NASA Astrophysics Data System (ADS)

Furer, V. L.; Vandyukov, A. E.; Majoral, J. P.; Caminade, A. M.; Kovalenko, V. I.

2016-09-01

The FTIR and FT Raman measurements of the phosphotrihydrazide (S)P[N(Me)-NH2]3 have been performed. This compound is a zero generation dendrimer G0 with terminal amine groups. Structural optimization and normal mode analysis were obtained for G0 by the density functional theory (DFT). Optimized geometric bond length and angles obtained by DFT show good agreement with experiment. The amine terminal groups are characterized by the well-defined bands at 3321, 3238, 1614 cm- 1 in the experimental IR spectrum and by bands at 3327, 3241 cm- 1 in the Raman spectrum of G0. The experimental frequencies of asymmetric and symmetric NH2 stretching vibrations of amine group are lower than theoretical values due to intramolecular Nsbnd H ⋯ S hydrogen bond. This hydrogen bond is also responsible for higher experimental infrared intensity of these bands as compared with theoretical values. Relying on DFT calculations a complete vibrational assignment is proposed for the studied dendrimer.

A theoretical study of the reaction of Ti+ with ethane

NASA Astrophysics Data System (ADS)

Moc, Jerzy; Fedorov, Dmitri G.; Gordon, Mark S.

2000-06-01

The doublet and quartet potential energy surfaces for the Ti++C2H6→TiC2H4++H2 and Ti++C2H6→TiCH2++CH4 reactions are studied using density functional theory (DFT) with the B3LYP functional and ab initio coupled cluster CCSD(T) methods with high quality basis sets. Structures have been optimized at the DFT level and the minima connected to each transition state (TS) by following the intrinsic reaction coordinate (IRC). Relative energies are calculated both at the DFT and coupled-cluster levels of theory. The relevant parts of the potential energy surface, especially key transition states, are also studied using multireference wave functions with the final energetics obtained with multireference second-order perturbation theory.

Exploiting the locality of periodic subsystem density-functional theory: efficient sampling of the Brillouin zone.

PubMed

Genova, Alessandro; Pavanello, Michele

2015-12-16

In order to approximately satisfy the Bloch theorem, simulations of complex materials involving periodic systems are made n(k) times more complex by the need to sample the first Brillouin zone at n(k) points. By combining ideas from Kohn-Sham density-functional theory (DFT) and orbital-free DFT, for which no sampling is needed due to the absence of waves, subsystem DFT offers an interesting middle ground capable of sizable theoretical speedups against Kohn-Sham DFT. By splitting the supersystem into interacting subsystems, and mapping their quantum problem onto separate auxiliary Kohn-Sham systems, subsystem DFT allows an optimal topical sampling of the Brillouin zone. We elucidate this concept with two proof of principle simulations: a water bilayer on Pt[1 1 1]; and a complex system relevant to catalysis-a thiophene molecule physisorbed on a molybdenum sulfide monolayer deposited on top of an α-alumina support. For the latter system, a speedup of 300% is achieved against the subsystem DTF reference by using an optimized Brillouin zone sampling (600% against KS-DFT).

First-principles analysis of structural and opto-electronic properties of indium tin oxide

NASA Astrophysics Data System (ADS)

Tripathi, Madhvendra Nath; Shida, Kazuhito; Sahara, Ryoji; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki

2012-05-01

Density functional theory (DFT) and DFT + U (DFT with on-site Coulomb repulsion corrections) calculations have been carried out to study the structural and opto-electronic properties of indium tin oxide (ITO) for both the oxidized and reduced environment conditions. Some of the results obtained by DFT calculations differ from the experimental observations, such as uncertain indication for the site preference of tin atom to replace indium atom at b-site or d-site, underestimation of local inward relaxation in the first oxygen polyhedra around tin atom, and also the improper estimation of electronic density of states and hence resulting in an inappropriate optical spectra of ITO. These discrepancies of theoretical outcomes with experimental observations in ITO arise mainly due to the underestimation of the cationic 4d levels within standard DFT calculations. Henceforth, the inclusion of on-site corrections within DFT + U framework significantly modifies the theoretical results in better agreement to the experimental observations. Within this framework, our calculations show that the indium b-site is preferential site over d-site for tin atom substitution in indium oxide under both the oxidized and reduced conditions. Moreover, the calculated average inward relaxation value of 0.16 Å around tin atom is in good agreement with the experimental value of 0.18 Å. Furthermore, DFT + U significantly modify the electronic structure and consequently induce modifications in the calculated optical spectra of ITO.

Ferrocene-isocoumarin conjugated molecules: synthesis, structural characterization, electronic properties, and DFT-TDDFT computational study.

PubMed

Peng, Ye-Dong; Zhou, Lin-Sen; Chen, Li-Li; Ma, Lu; Zhao, Yue; Zhang, Wen-Wei; Zuo, Jing-Lin

2015-08-28

Two ferrocene-isocoumarin conjugated molecules, methyl 3-ferrocenyl-1-oxo-1H-isochromene-6-carboxylate () and 3,8-bisferrocenylpyrano[3,4-g]isochromene-1,6-dione (), have been synthesized through the acid-prompted regioselective oxidative cyclization from dimethyl 2-(ferrocenylethynyl)terephthalate () and dimethyl 2,5-bis(ferrocenylethynyl)terephthalate (), respectively. Single-crystal X-ray diffraction, together with the density functional theory (DFT) calculations, shows that the ferrocene-isocoumarin conjugated compounds display better coplanarity than the corresponding ferrocenylethynyl terephthalates. All the compounds exhibit characteristic MLCT, ICT and π-π* transitions in the UV-visible range in solution, and and show higher oscillator strength of the absorption than and , which are verified by time-dependent DFT (TDDFT) theoretical calculations. The electrochemical properties are studied by cyclic voltammetry (CV), which are also in accord with the theoretical calculations.

Spectroscopic investigations (FT-IR, UV, 1H and 13C NMR) and DFT/TD-DFT calculations of potential analgesic drug 2-[2-(dimethylamino)ethyl]-6-methoxy-4-(pyridin-2-yl)-1(2H)-phthalazinone

NASA Astrophysics Data System (ADS)

Sroczyński, Dariusz; Malinowski, Zbigniew

2017-12-01

The theoretical molecular geometry and the IR, UV, 1H and 13C NMR spectroscopic properties of 2-[2-(dimethylamino)ethyl]-6-methoxy-4-(pyridin-2-yl)-1(2H)-phthalazinone with the previously demonstrated in vivo analgesic activity were characterized. The conformational analysis, performed using the molecular mechanics method with the General AMBER Force Field (GAFF) and the Density Functional Theory (DFT) approach with the B3LYP hybrid functional and the 6-31 + g(d) basis sets, allowed to determine the most stable rotamer. The theoretical molecular geometry of this conformer was then calculated at the B3LYP/6-311++g(d,p) level of theory, and its phthalazinone core was compared with the experimental geometry of 1(2H)-phthalazinone. The calculated vibrational frequencies and the potential energy distribution enabled to assign the theoretical vibrational modes to the experimental FT-IR bands. The UV spectrum calculated with the Time-Dependent Density Functional Theory (TD-DFT) method in methanol identified the main electronic transitions and their character. 1H and 13C NMR chemical shifts simulated by the Gauge-Independent Atomic Orbital (GIAO) method in chloroform confirmed the previous assignment of the experimental resonance signals. The stability of the molecule was considered taking into account the hyperconjugation and electron density delocalization effects evaluated by the Natural Bond Orbital (NBO) method. The calculated spatial distribution of molecular electrostatic potential made possible to estimate the regions with nucleophilic and electrophilic properties. The results of the potentiodynamic polarization measurements were also indicated the corrosion inhibition activity of the title compound on 100Cr6 bearing steel in 1 mol dm-3 HCl solution.

Recent Progress in Treating Protein-Ligand Interactions with Quantum-Mechanical Methods.

PubMed

Yilmazer, Nusret Duygu; Korth, Martin

2016-05-16

We review the first successes and failures of a "new wave" of quantum chemistry-based approaches to the treatment of protein/ligand interactions. These approaches share the use of "enhanced", dispersion (D), and/or hydrogen-bond (H) corrected density functional theory (DFT) or semi-empirical quantum mechanical (SQM) methods, in combination with ensemble weighting techniques of some form to capture entropic effects. Benchmark and model system calculations in comparison to high-level theoretical as well as experimental references have shown that both DFT-D (dispersion-corrected density functional theory) and SQM-DH (dispersion and hydrogen bond-corrected semi-empirical quantum mechanical) perform much more accurately than older DFT and SQM approaches and also standard docking methods. In addition, DFT-D might soon become and SQM-DH already is fast enough to compute a large number of binding modes of comparably large protein/ligand complexes, thus allowing for a more accurate assessment of entropic effects.

Molecular structure, vibrational spectra and DFT molecular orbital calculations (TD-DFT and NMR) of the antiproliferative drug Methotrexate

NASA Astrophysics Data System (ADS)

Ayyappan, S.; Sundaraganesan, N.; Aroulmoji, V.; Murano, E.; Sebastian, S.

2010-09-01

The FT-IR and FT-Raman spectral studies of the Methotrexate (MTX) were carried out. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of MTX have been investigated with the help of B3LYP density functional theory (DFT) using 6-31G(d) as basis set. Detailed analysis of the vibrational spectra has been made with the aid of theoretically predicted vibrational frequencies. The vibrational analysis confirms the differently acting ring modes, steric repulsion, conjugation and back-donation. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complement with the experimental findings. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Good correlations between the experimental 1H and 13C NMR chemical shifts in DMSO solution and calculated GIAO shielding tensors were found.

Electronic structure, transport, and collective effects in molecular layered systems.

PubMed

Hahn, Torsten; Ludwig, Tim; Timm, Carsten; Kortus, Jens

2017-01-01

The great potential of organic heterostructures for organic device applications is exemplified by the targeted engineering of the electronic properties of phthalocyanine-based systems. The transport properties of two different phthalocyanine systems, a pure copper phthalocyanine (CoPc) and a flourinated copper phthalocyanine-manganese phthalocyanine (F 16 CoPc/MnPc) heterostructure, are investigated by means of density functional theory (DFT) and the non-equilibrium Green's function (NEGF) approach. Furthermore, a master-equation-based approach is used to include electronic correlations beyond the mean-field-type approximation of DFT. We describe the essential theoretical tools to obtain the parameters needed for the master equation from DFT results. Finally, an interacting molecular monolayer is considered within a master-equation approach.

Molecular structure and vibrational spectra of Irinotecan: a density functional theoretical study.

PubMed

Chinna Babu, P; Sundaraganesan, N; Sudha, S; Aroulmoji, V; Murano, E

2012-12-01

The solid phase FTIR and FT-Raman spectra of Irinotecan have been recorded in the regions 400-4000 and 50-4000 cm(-1), respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The structure of the molecule was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(d) as basis set. The vibrational frequencies were calculated for Irinotecan by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. The infrared spectrum was also simulated from the calculated intensities. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations. Copyright © 2012 Elsevier B.V. All rights reserved.

Theoretical study of the ammonia nitridation rate on an Fe (100) surface: a combined density functional theory and kinetic Monte Carlo study.

PubMed

Yeo, Sang Chul; Lo, Yu Chieh; Li, Ju; Lee, Hyuck Mo

2014-10-07

Ammonia (NH3) nitridation on an Fe surface was studied by combining density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. A DFT calculation was performed to obtain the energy barriers (Eb) of the relevant elementary processes. The full mechanism of the exact reaction path was divided into five steps (adsorption, dissociation, surface migration, penetration, and diffusion) on an Fe (100) surface pre-covered with nitrogen. The energy barrier (Eb) depended on the N surface coverage. The DFT results were subsequently employed as a database for the kMC simulations. We then evaluated the NH3 nitridation rate on the N pre-covered Fe surface. To determine the conditions necessary for a rapid NH3 nitridation rate, the eight reaction events were considered in the kMC simulations: adsorption, desorption, dissociation, reverse dissociation, surface migration, penetration, reverse penetration, and diffusion. This study provides a real-time-scale simulation of NH3 nitridation influenced by nitrogen surface coverage that allowed us to theoretically determine a nitrogen coverage (0.56 ML) suitable for rapid NH3 nitridation. In this way, we were able to reveal the coverage dependence of the nitridation reaction using the combined DFT and kMC simulations.

Structure of electric double layers in capacitive systems and to what extent (classical) density functional theory describes it

NASA Astrophysics Data System (ADS)

Härtel, Andreas

2017-10-01

Ongoing scientific interest is aimed at the properties and structure of electric double layers (EDLs), which are crucial for capacitive energy storage, water treatment, and energy harvesting technologies like supercapacitors, desalination devices, blue engines, and thermocapacitive heat-to-current converters. A promising tool to describe their physics on a microscopic level is (classical) density functional theory (DFT), which can be applied in order to analyze pair correlations and charge ordering in the primitive model of charged hard spheres. This simple model captures the main properties of ionic liquids and solutions and it predicts many of the phenomena that occur in EDLs. The latter often lead to anomalous response in the differential capacitance of EDLs. This work constructively reviews the powerful theoretical framework of DFT and its recent developments regarding the description of EDLs. It explains to what extent current approaches in DFT describe structural ordering and in-plane transitions in EDLs, which occur when the corresponding electrodes are charged. Further, the review briefly summarizes the history of modeling EDLs, presents applications, and points out limitations and strengths in present theoretical approaches. It concludes that DFT as a sophisticated microscopic theory for ionic systems is expecting a challenging but promising future in both fundamental research and applications in supercapacitive technologies.

Electronic and magnetic properties of small rhodium clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soon, Yee Yeen; Yoon, Tiem Leong; Lim, Thong Leng

2015-04-24

We report a theoretical study of the electronic and magnetic properties of rhodium-atomic clusters. The lowest energy structures at the semi-empirical level of rhodium clusters are first obtained from a novel global-minimum search algorithm, known as PTMBHGA, where Gupta potential is used to describe the atomic interaction among the rhodium atoms. The structures are then re-optimized at the density functional theory (DFT) level with exchange-correlation energy approximated by Perdew-Burke-Ernzerhof generalized gradient approximation. For the purpose of calculating the magnetic moment of a given cluster, we calculate the optimized structure as a function of the spin multiplicity within the DFT framework.more » The resultant magnetic moments with the lowest energies so obtained allow us to work out the magnetic moment as a function of cluster size. Rhodium atomic clusters are found to display a unique variation in the magnetic moment as the cluster size varies. However, Rh{sub 4} and Rh{sub 6} are found to be nonmagnetic. Electronic structures of the magnetic ground-state structures are also investigated within the DFT framework. The results are compared against those based on different theoretical approaches available in the literature.« less

Experimental FT-IR, Laser-Raman and DFT spectroscopic analysis of 2,3,4,5,6-Pentafluoro-trans-cinnamic acid.

PubMed

Sert, Yusuf; Doğan, Hatice; Navarrete, Angélica; Somanathan, Ratnasamy; Aguirre, Gerardo; Çırak, Çağrı

2014-07-15

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized 2,3,4,5,6-Pentafluoro-trans-cinnamic acid have been investigated. The experimental FT-IR (4000-400 cm(-1)) and Laser-Raman spectra (4000-100 cm(-1)) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parameterized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with the results in the literature. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and depicted. Copyright © 2014 Elsevier B.V. All rights reserved.

Experimental (FT-IR, NMR and UV) and theoretical (M06-2X and DFT) investigation, and frequency estimation analyses on (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile

NASA Astrophysics Data System (ADS)

Sert, Yusuf; Balakit, Asim A.; Öztürk, Nuri; Ucun, Fatih; El-Hiti, Gamal A.

2014-10-01

The spectroscopic properties of (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile have been investigated by FT-IR, UV, 1H and 13C NMR techniques. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parameterized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been carried out by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies were in good agreement with the corresponding experimental data, and with the results in the literature. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength wavelengths were performed by B3LYP methods. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and depicted.

Experimental and Theoretical Reduction Potentials of Some Biologically Active ortho-Carbonyl para-Quinones.

PubMed

Martínez-Cifuentes, Maximiliano; Salazar, Ricardo; Ramírez-Rodríguez, Oney; Weiss-López, Boris; Araya-Maturana, Ramiro

2017-04-04

The rational design of quinones with specific redox properties is an issue of great interest because of their applications in pharmaceutical and material sciences. In this work, the electrochemical behavior of a series of four p -quinones was studied experimentally and theoretically. The first and second one-electron reduction potentials of the quinones were determined using cyclic voltammetry and correlated with those calculated by density functional theory (DFT) using three different functionals, BHandHLYP, M06-2x and PBE0. The differences among the experimental reduction potentials were explained in terms of structural effects on the stabilities of the formed species. DFT calculations accurately reproduced the first one-electron experimental reduction potentials with R ² higher than 0.94. The BHandHLYP functional presented the best fit to the experimental values ( R ² = 0.957), followed by M06-2x ( R ² = 0.947) and PBE0 ( R ² = 0.942).

Theoretical modeling of the electronic structure and exchange interactions in Cu(II)Pc

NASA Astrophysics Data System (ADS)

Wu, Wei; Fisher, A. J.; Harrison, N. M.; Wang, Hai; Wu, Zhenlin; Gardener, Jules; Heutz, Sandrine; Jones, Tim; Aeppli, Gabriel

2012-12-01

We calculate the electronic structure and exchange interactions in a copper(II)phthalocyanine (Cu(II)Pc) crystal as a one-dimensional molecular chain using hybrid exchange density functional theory (DFT). In addition, the intermolecular exchange interactions are also calculated in a molecular dimer using Green's function perturbation theory (GFPT) to illustrate the underlying physics. We find that the exchange interactions depend strongly on the stacking angle, but weakly on the sliding angle (defined in the text). The hybrid DFT calculations also provide an insight into the electronic structure of the Cu(II)Pc molecular chain and demonstrate that on-site electron correlations have a significant effect on the nature of the ground state, the band gap and magnetic excitations. The exchange interactions predicted by our DFT calculations and GFPT calculations agree qualitatively with the recent experimental results on newly found η-Cu(II)Pc and the previous results for the α- and β-phases. This work provides a reliable theoretical basis for the further application of Cu(II)Pc to molecular spintronics and organic-based quantum information processing.

Theoretical modeling of the electronic structure and exchange interactions in a Cu(II)Pc one-dimensional chain

NASA Astrophysics Data System (ADS)

Wu, Wei; Fisher, A. J.; Harrison, N. M.

2011-07-01

We calculate the electronic structure and exchange interactions in a copper(II)phthalocyanine [Cu(II)Pc] crystal as a one-dimensional molecular chain using hybrid exchange density functional theory (DFT). In addition, the intermolecular exchange interactions are also calculated in a molecular dimer using Green’s function perturbation theory (GFPT) to illustrate the underlying physics. We find that the exchange interactions depend strongly on the stacking angle, but weakly on the sliding angle (defined in the text). The hybrid DFT calculations also provide an insight into the electronic structure of the Cu(II)Pc molecular chain and demonstrate that on-site electron correlations have a significant effect on the nature of the ground state, the band gap, and magnetic excitations. The exchange interactions predicted by our DFT calculations and GFPT calculations agree qualitatively with the recent experimental results on newly found η-Cu(II)Pc and the previous results for the α and β phases. This work provides a reliable theoretical basis for the further application of Cu(II)Pc to molecular spintronics and organic-based quantum information processing.

Vibrational frequency analysis, FT-IR, DFT and M06-2X studies on tert-Butyl N-(thiophen-2yl)carbamate

NASA Astrophysics Data System (ADS)

Sert, Yusuf; Singer, L. M.; Findlater, M.; Doğan, Hatice; Çırak, Ç.

2014-07-01

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized tert-Butyl N-(thiophen-2yl)carbamate have been investigated. The experimental FT-IR (4000-400 cm-1) spectrum of the molecule in the solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with the 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The vibrational frequencies have been assigned using potential energy distribution (PED) analysis by using VEDA 4 software. The computational optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with related literature results. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and are depicted.

Reactive sites influence in PMMA oligomers reactivity: a DFT study

NASA Astrophysics Data System (ADS)

Paz, C. V.; Vásquez, S. R.; Flores, N.; García, L.; Rico, J. L.

2018-01-01

In this work, we present a theoretical study of methyl methacrylate (MMA) living anionic polymerization. The study was addressed to understanding two important experimental observations made for Michael Szwarc in 1956. The unexpected effect of reactive sites concentration in the propagation rate, and the self-killer behavior of MMA (deactivating of living anionic polymerization). The theoretical calculations were performed by density functional theory (DFT) to obtain the frontier molecular orbitals values. These values were used to calculate and analyze the chemical interaction descriptors in DFT-Koopmans’ theorem. As a result, it was observed that the longest chain-length species (related with low concentration of reactive sites) exhibit the highest reactivity (behavior associated with the increase of the propagation rate). The improvement in this reactivity was attributed to the crosslinking produced in the polymethyl methacrylate chains. Meanwhile, the self-killer behavior was associated with the intermolecular forces present in the reactive sites. This behavior was associated to an obstruction in solvation, since the active sites remained active through all propagation species. The theoretical results were in good agreement with the Szwarc experiments.

Self-consistent DFT +U method for real-space time-dependent density functional theory calculations

NASA Astrophysics Data System (ADS)

Tancogne-Dejean, Nicolas; Oliveira, Micael J. T.; Rubio, Angel

2017-12-01

We implemented various DFT+U schemes, including the Agapito, Curtarolo, and Buongiorno Nardelli functional (ACBN0) self-consistent density-functional version of the DFT +U method [Phys. Rev. X 5, 011006 (2015), 10.1103/PhysRevX.5.011006] within the massively parallel real-space time-dependent density functional theory (TDDFT) code octopus. We further extended the method to the case of the calculation of response functions with real-time TDDFT+U and to the description of noncollinear spin systems. The implementation is tested by investigating the ground-state and optical properties of various transition-metal oxides, bulk topological insulators, and molecules. Our results are found to be in good agreement with previously published results for both the electronic band structure and structural properties. The self-consistent calculated values of U and J are also in good agreement with the values commonly used in the literature. We found that the time-dependent extension of the self-consistent DFT+U method yields improved optical properties when compared to the empirical TDDFT+U scheme. This work thus opens a different theoretical framework to address the nonequilibrium properties of correlated systems.

Melting slope of MgO from molecular dynamics and density functional theory

NASA Astrophysics Data System (ADS)

Tangney, Paul; Scandolo, Sandro

2009-09-01

We combine density functional theory (DFT) with molecular dynamics simulations based on an accurate atomistic force field to calculate the pressure derivative of the melting temperature of magnesium oxide at ambient pressure—a quantity for which a serious disagreement between theory and experiment has existed for almost 15 years. We find reasonable agreement with previous DFT results and with a very recent experimental determination of the slope. We pay particular attention to areas of possible weakness in theoretical calculations and conclude that the long-standing discrepancy with experiment could only be explained by a dramatic failure of existing density functionals or by flaws in the original experiment.

Accuracy of color prediction of anthraquinone dyes in methanol solution estimated from first principle quantum chemistry computations.

PubMed

Cysewski, Piotr; Jeliński, Tomasz

2013-10-01

The electronic spectrum of four different anthraquinones (1,2-dihydroxyanthraquinone, 1-aminoanthraquinone, 2-aminoanthraquinone and 1-amino-2-methylanthraquinone) in methanol solution was measured and used as reference data for theoretical color prediction. The visible part of the spectrum was modeled according to TD-DFT framework with a broad range of DFT functionals. The convoluted theoretical spectra were validated against experimental data by a direct color comparison in terms of CIE XYZ and CIE Lab tristimulus model color. It was found, that the 6-31G** basis set provides the most accurate color prediction and there is no need to extend the basis set since it does not improve the prediction of color. Although different functionals were found to give the most accurate color prediction for different anthraquinones, it is possible to apply the same DFT approach for the whole set of analyzed dyes. Especially three functionals seem to be valuable, namely mPW1LYP, B1LYP and PBE0 due to very similar spectra predictions. The major source of discrepancies between theoretical and experimental spectra comes from L values, representing the lightness, and the a parameter, depicting the position on green→magenta axis. Fortunately, the agreement between computed and observed blue→yellow axis (parameter b) is very precise in the case of studied anthraquinone dyes in methanol solution. Despite discussed shortcomings, color prediction from first principle quantum chemistry computations can lead to quite satisfactory results, expressed in terms of color space parameters.

C2 Fragmentation Energy of C60 Revisited: Theory Disagrees with Most Experiments

NASA Technical Reports Server (NTRS)

Boese, A. Daniel; Scuseria, Gustavo E.

1998-01-01

Following our earlier work on the subject, we have carried out density functional theory (DFT) and second-order Moller-Plesset perturbation theory (MP2) calculations of the dissociation energy of the reaction C60 yields C58 + C2 using polarized basis sets and geometries optimized with DFT methods. The present theoretical results support an electronic fragmentation energy D(sub e) around 10-11 eV in disagreement with most experimental results that place the dissociation energy D(sub o) (including zero point energy) around 7-8 eV. The plausible errors remaining in the theoretical calculations are unlikely to account for this big difference (2-4 eV).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gifford, Brendan Joel; Kilina, Svetlana; Htoon, Han

Recent spectroscopic studies have revealed the appearance of multiple low-energy peaks in the fluorescence of single-walled carbon nanotubes (SWCNTs) upon their covalent functionalization by aryl groups. The photophysical nature of these low energy optical bands is of significant interest in the quest to understand their appearance and to achieve their precise control via chemical modification of SWCNTs. This theoretical study explains the specific energy dependence of emission features introduced in chemically functionalized (6,5) SWCNTs with aryl bromides at different conformations and in various dielectric media. Calculations using density functional theory (DFT) and time dependent DFT (TD-DFT) show that the specificmore » isomer geometry—the relative position of functional groups on the carbon-ring of the nanotube—is critical for controlling the energies and intensities of optical transitions introduced by functionalization, while the dielectric environment and the chemical composition of functional groups play less significant roles. Furthermore, the predominant effects on optical properties as a result of functionalization conformation are rationalized by exciton localization on the surface of the SWCNT near the dopant sp3-defect but not onto the functional group itself.« less

Synthesis, molecular structure, vibrational spectroscopy, optical investigation and DFT study of a novel hybrid material: 3,3‧-diammoniumdiphenylsulfone hexachloridostannate monohydrate

NASA Astrophysics Data System (ADS)

Kessentini, A.; Dammak, T.; Belhouchet, M.

2017-12-01

In his work we investigate a new halogenotin (IV) organic inorganic material. The structure, determined by single-crystal X-ray diffraction at 293 K of 3,3‧-diammoniumdiphenylsulfone hexachloridostannate monohydrate abbreviated 3,3‧(DDS)SnCl6, can be viewed as inorganic layers built from (SnCl6)2- octahedra and H2O molecules, between which, the organic entities [C12H14N2O2S]2+ are inserted. Experimental room-temperature X-ray studies were supported by theoretical methods using density functional theory (DFT). The detailed examination of the vibrational spectra of our material was correlated by DFT calculation using the unit cell parameters obtained from the experiment data. The optical properties in the UV-visible region have been explored by the UV-visible absorption. This material shows a single absorption band centred at 325 nm (318 eV). The energy difference between Occupied, HOMO and Lowest Unoccupied, LUMO orbital which is called energy gap can be used to predict the strength and stability of metal complexes, as well as in determining molecular electrical transport properties. For the calculation of excitation energies in the optical studies we used Time-Dependent Density Functional Theory (TD-DFT). In addition, Mulliken population method and molecular electrostatic potential (MEP) of the title material have been theoretically studied by GAUSSIAN 03 package.

Theoretical study of the ammonia nitridation rate on an Fe (100) surface: A combined density functional theory and kinetic Monte Carlo study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeo, Sang Chul; Lee, Hyuck Mo, E-mail: hmlee@kaist.ac.kr; Lo, Yu Chieh

2014-10-07

Ammonia (NH{sub 3}) nitridation on an Fe surface was studied by combining density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. A DFT calculation was performed to obtain the energy barriers (E{sub b}) of the relevant elementary processes. The full mechanism of the exact reaction path was divided into five steps (adsorption, dissociation, surface migration, penetration, and diffusion) on an Fe (100) surface pre-covered with nitrogen. The energy barrier (E{sub b}) depended on the N surface coverage. The DFT results were subsequently employed as a database for the kMC simulations. We then evaluated the NH{sub 3} nitridation rate onmore » the N pre-covered Fe surface. To determine the conditions necessary for a rapid NH{sub 3} nitridation rate, the eight reaction events were considered in the kMC simulations: adsorption, desorption, dissociation, reverse dissociation, surface migration, penetration, reverse penetration, and diffusion. This study provides a real-time-scale simulation of NH{sub 3} nitridation influenced by nitrogen surface coverage that allowed us to theoretically determine a nitrogen coverage (0.56 ML) suitable for rapid NH{sub 3} nitridation. In this way, we were able to reveal the coverage dependence of the nitridation reaction using the combined DFT and kMC simulations.« less

Polymer density functional theory approach based on scaling second-order direct correlation function.

PubMed

Zhou, Shiqi

2006-06-01

A second-order direct correlation function (DCF) from solving the polymer-RISM integral equation is scaled up or down by an equation of state for bulk polymer, the resultant scaling second-order DCF is in better agreement with corresponding simulation results than the un-scaling second-order DCF. When the scaling second-order DCF is imported into a recently proposed LTDFA-based polymer DFT approach, an originally associated adjustable but mathematically meaningless parameter now becomes mathematically meaningful, i.e., the numerical value lies now between 0 and 1. When the adjustable parameter-free version of the LTDFA is used instead of the LTDFA, i.e., the adjustable parameter is fixed at 0.5, the resultant parameter-free version of the scaling LTDFA-based polymer DFT is also in good agreement with the corresponding simulation data for density profiles. The parameter-free version of the scaling LTDFA-based polymer DFT is employed to investigate the density profiles of a freely jointed tangent hard sphere chain near a variable sized central hard sphere, again the predictions reproduce accurately the simulational results. Importance of the present adjustable parameter-free version lies in its combination with a recently proposed universal theoretical way, in the resultant formalism, the contact theorem is still met by the adjustable parameter associated with the theoretical way.

Molecular structure, spectroscopic studies and first-order molecular hyperpolarizabilities of ferulic acid by density functional study

NASA Astrophysics Data System (ADS)

Sebastian, S.; Sundaraganesan, N.; Manoharan, S.

2009-10-01

Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of ferulic acid (FA) (4-hydroxy-3-methoxycinnamic acid) were carried out by using density functional (DFT/B3LYP/BLYP) method with 6-31G(d,p) as basis set. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The vibrational spectral data obtained from solid phase FT-IR and FT-Raman spectra are assigned based on the results of the theoretical calculations. The observed spectra are found to be in good agreement with calculated values. The electric dipole moment ( μ) and the first hyperpolarizability ( β) values of the investigated molecule have been computed using ab initio quantum mechanical calculations. The calculation results also show that the FA molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values. A detailed interpretation of the infrared and Raman spectra of FA was also reported. The energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) results complements with the experimental findings. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The theoretical FT-IR and FT-Raman spectra for the title molecule have been constructed.

Experimental (FT-IR, NMR and UV) and theoretical (M06-2X and DFT) investigation, and frequency estimation analyses on (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile.

PubMed

Sert, Yusuf; Balakit, Asim A; Öztürk, Nuri; Ucun, Fatih; El-Hiti, Gamal A

2014-10-15

The spectroscopic properties of (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile have been investigated by FT-IR, UV, (1)H and (13)C NMR techniques. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parameterized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been carried out by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies were in good agreement with the corresponding experimental data, and with the results in the literature. (1)H and (13)C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength wavelengths were performed by B3LYP methods. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and depicted. Copyright © 2014 Elsevier B.V. All rights reserved.

Synthesis, crystal structure, vibrational spectroscopy, optical properties and theoretical studies of a new organic-inorganic hybrid material: [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2.

PubMed

Ben Ahmed, A; Feki, H; Abid, Y

2014-12-10

A new organic-inorganic hybrid material, [((CH3)2NH2)(+)]6·[(BiBr6)(3-)]2, has been synthesized and characterized by X-ray diffraction, FT-IR, Raman spectroscopy and UV-Visible absorption. The studied compound crystallizes in the triclinic system, space group P1¯ with the following parameters: a=8.4749(6)(Å), b=17.1392(12)(Å), c=17.1392(12)(Å), α=117.339(0)°, β=99.487(0)°, γ=99.487(0)° and Z=2. The crystal lattice is composed of a two discrete (BiBr6)(3-) anions surrounded by six ((CH3)2NH2)(+) cations. Complex hydrogen bonding interactions between (BiBr6)(3-) and organic cations from a three-dimensional network. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra and optical properties of the investigated molecule in the ground state. The full geometry optimization of designed system is performed using DFT method at B3LYP/LanL2DZ level of theory using the Gaussian03. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The vibrational spectral data obtained from FT-IR and Raman spectra are assigned based on the results of the theoretical calculations. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental UV-Visible spectrum. The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO-LUMO boundary. Copyright © 2014 Elsevier B.V. All rights reserved.

Regarding the use and misuse of retinal protonated Schiff base photochemistry as a test case for time-dependent density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valsson, Omar; Filippi, Claudia, E-mail: c.filippi@utwente.nl; Casida, Mark E., E-mail: mark.casida@ujf-grenoble.fr

2015-04-14

The excited-state relaxation of retinal protonated Schiff bases (PSBs) is an important test case for biological applications of time-dependent (TD) density-functional theory (DFT). While well-known shortcomings of approximate TD-DFT might seem discouraging for application to PSB relaxation, progress continues to be made in the development of new functionals and of criteria allowing problematic excitations to be identified within the framework of TD-DFT itself. Furthermore, experimental and theoretical ab initio advances have recently lead to a revised understanding of retinal PSB photochemistry, calling for a reappraisal of the performance of TD-DFT in describing this prototypical photoactive system. Here, we re-investigate themore » performance of functionals in (TD-)DFT calculations in light of these new benchmark results, which we extend to larger PSB models. We focus on the ability of the functionals to describe primarily the early skeletal relaxation of the chromophore and investigate how far along the out-of-plane pathways these functionals are able to describe the subsequent rotation around formal single and double bonds. Conventional global hybrid and range-separated hybrid functionals are investigated as the presence of Hartree-Fock exchange reduces problems with charge-transfer excitations as determined by the Peach-Benfield-Helgaker-Tozer Λ criterion and by comparison with multi-reference perturbation theory results. While we confirm that most functionals cannot render the complex photobehavior of the retinal PSB, do we also observe that LC-BLYP gives the best description of the initial part of the photoreaction.« less

Theoretical and Experimental Spectroscopic Analysis of Cyano-Substituted Styrylpyridine Compounds

PubMed Central

Castro, Maria Eugenia; Percino, Maria Judith; Chapela, Victor M.; Ceron, Margarita; Soriano-Moro, Guillermo; Lopez-Cruz, Jorge; Melendez, Francisco J.

2013-01-01

A combined theoretical and experimental study on the structure, infrared, UV-Vis and 1H NMR data of trans-2-(m-cyanostyryl)pyridine, trans-2-[3-methyl-(m-cyanostyryl)] pyridine and trans-4-(m-cyanostyryl)pyridine is presented. The synthesis was carried out with an efficient Knoevenagel condensation using green chemistry conditions. Theoretical geometry optimizations and their IR spectra were carried out using the Density Functional Theory (DFT) in both gas and solution phases. For theoretical UV-Vis and 1H NMR spectra, the Time-Dependent DFT (TD-DFT) and the Gauge-Including Atomic Orbital (GIAO) methods were used, respectively. The theoretical characterization matched the experimental measurements, showing a good correlation. The effect of cyano- and methyl-substituents, as well as of the N-atom position in the pyridine ring on the UV-Vis, IR and NMR spectra, was evaluated. The UV-Vis results showed no significant effect due to electron-withdrawing cyano- and electron-donating methyl-substituents. The N-atom position, however, caused a slight change in the maximum absorption wavelengths. The IR normal modes were assigned for the cyano- and methyl-groups. 1H NMR spectra showed the typical doublet signals due to protons in the trans position of a double bond. The theoretical characterization was visibly useful to assign accurately the signals in IR and 1H NMR spectra, as well as to identify the most probable conformation that could be present in the formation of the styrylpyridine-like compounds. PMID:23429190

The crystallographic, spectroscopic and theoretical studies on (E)-2-(((4-chlorophenyl)imino)methyl)-5-(diethylamino)phenol and (E)-2-(((3-chlorophenyl)imino)methyl)-5-(diethylamino)phenol molecules

NASA Astrophysics Data System (ADS)

Demirtaş, Güneş; Dege, Necmi; Ağar, Erbil; Uzun, Sümeyye Gümüş

2018-01-01

Two new salicylideneaniline (SA) derivative compounds (E)-2-(((4-chlorophenyl)imino)methyl)-5-(diethylamino)phenol, compound (I), and (E)-2-(((3-chlorophenyl)imino)methyl)-5-(diethylamino)phenol, compound (II), have been synthesized and characterized by single crystal X-ray diffraction, IR spectroscopy, 1H NMR, 13C NMR and theoretical methods. Both of the compounds which are Schiff base derivatives are isomer of each other. While the compound (I) crystallizes in centrosymmetric monoclinic space group P 21/c, the compound (II) crystallizes in orthorhombic space group P 212121. The theoretical parameters of the molecules have been calculated by using Hartree-Fock (HF) and density functional theory (DFT/B3LYP) with 6-31G (d,p) basis set. These theoretical parameters have been compared with the experimental parameters obtained by XRD. The experimental geometries of the compounds have been superimposed with the theoretical geometries calculated by HF and DFT methods. Furthermore, the theoretical IR calculations, molecular electrostatic potential maps (MEP) and frontier molecular orbitals have been created for the compounds.

Synthesis, theoretical studies and molecular docking of a novel chlorinated tetracyclic: (Z/E)-3-(1,8-dichloro-9,10-dihydro-9,10-ethanoanthracen-11-yl)acrylaldehyde

NASA Astrophysics Data System (ADS)

Sultan, Mujeeb A.; Almansour, Abdulrahman I.; Pillai, Renjith Raveendran; Kumar, Raju Suresh; Arumugam, Natarajan; Armaković, Stevan; Armaković, Sanja J.; Soliman, Saied M.

2017-12-01

(Z/E)-3-(1,8-Dichloro-9,10-dihydro-9,10-ethanoanthracen-11-yl)acrylaldehyde 2 has been investigated experimentally and theoretically. The Wittig reaction of 1,8-dichloro-9,10-dihydro-9,10-ethanoanthracene-11-carbaldehyde 1 and (triphenylphosphoranylidene) acetaldehyde in toluene under reflux conditions resulted in compound 2. Spectroscopic characterization of compound 2 was performed by the Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and high-resolution mass spectroscopy techniques. Density functional theory (DFT) calculations were conducted to study various global and local reactive properties. The spectra were also obtained by DFT calculations and corresponding comparisons were performed to validate the level of theory. Using DFT calculations, reactivity has been studied based on frontier molecular orbitals, charge distribution, average local ionization energies, Fukui functions, and bond dissociation energies for hydrogen abstraction. Molecular dynamics simulations have been used to investigate the influence of water as a solvent for compound 2. Finally, compound 2 was docked into the central and allosteric binding sites of the serotonin transporter enzyme and was found to be a good candidate as an antidepressant-like compound.

Vibrational frequency analysis, FT-IR, DFT and M06-2X studies on tert-Butyl N-(thiophen-2yl)carbamate.

PubMed

Sert, Yusuf; Singer, L M; Findlater, M; Doğan, Hatice; Çırak, Ç

2014-07-15

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized tert-Butyl N-(thiophen-2yl)carbamate have been investigated. The experimental FT-IR (4000-400 cm(-1)) spectrum of the molecule in the solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with the 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The vibrational frequencies have been assigned using potential energy distribution (PED) analysis by using VEDA 4 software. The computational optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with related literature results. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and are depicted. Copyright © 2014 Elsevier B.V. All rights reserved.

Understanding the effects of Cr doping in rutile TiO2 by DFT calculations and X-ray spectroscopy.

PubMed

Vásquez, G Cristian; Maestre, David; Cremades, Ana; Ramírez-Castellanos, Julio; Magnano, Elena; Nappini, Silvia; Karazhanov, Smagul Zh

2018-06-07

The effects of Cr on local environment and electronic structure of rutile TiO 2 are studied combining theoretical and experimental approaches. Neutral and negatively charged substitutional Cr impurities Cr Ti 0 and Cr Ti 1- as well as Cr-oxygen vacancy complex 2Cr Ti  + V O are studied by the density functional theory (DFT) within the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) functional. Experimental results based on X-Ray absorption spectroscopy (XAS) and X-Ray photoelectron spectroscopy (XPS) performed on Cr doped TiO 2 at the Synchrotron facility were compared to the theoretical results. It is shown that the electrons of the oxygen vacancy tend to be localized at the t 2g states of the Cr ions in order to reach the stable oxidation state of Cr 3+ . Effects of Cr on crystal field (CF) and structural distortions in the rutile TiO 2 cell were analyzed by the DFT calculations and XAS spectra revealing that the CF and tetragonal distortions in TiO 2 are very sensitive to the concentration of Cr.

Natural dye extracted from karkadah and its application in dye-sensitized solar cells: experimental and density functional theory study.

PubMed

Reda, S M; Soliman, K A

2016-02-01

This work presents an experimental and theoretical study of cyanidin natural dye as a sensitizer for ZnO dye-sensitized solar cells. ZnO nanoparticles were prepared using ammonia and oxalic acid as a capping agent. The calculated average size of the synthesized ZnO with different capping agents was found to be 32.1 nm. Electronic properties of cyanidin and delphinidin dye were studied using density functional theory (DFT) and time-dependent DFT with a B3LYP/6-31G(d,p) level. By comparing the theoretical results with the experimental data, the cyanidin dye can be used as a sensitizer in dye-sensitized solar cells. An efficiency of 0.006% under an AM-1.5 illumination at 100  mW/cm(2) was attained. The influence of dye adsorption time on the solar cell performance is discussed.

Experimental and theoretical studies on the structure and spectroscopic properties of (E)-1-(2-aminophenyl)-3-(pyridine-4-yl) prop-2-en-1-one

NASA Astrophysics Data System (ADS)

Cruz Ortiz, Andrés Felipe; Sánchez López, Alberto; García Ríos, Alejandro; Cuenú Cabezas, Fernando; Rozo Correa, Ciro Eduardo

2015-10-01

(E)-1-(2-aminophenyl)-3-(pyridine-4-yl)prop-2-en-1-one (or simply 2-aminochalcone) was synthetized and characterized by elemental analysis, FT-IR, NMR, MS and XRD. Molecular geometry optimization, vibrational harmonic frequencies, 1H and 13C NMR chemical shifts were calculated by ab initio (HF and MP2) and density functional theory (DFT) methods, with B3LYP and B3PW91 functionals, using GAUSSIAN 09 program package without any constraint on the geometry. With VEDA software vibrational frequencies were assigned in terms of the potential energy distribution. A detailed interpretation of the FT-IR, NMR and XRD, experimental and calculated, is reported. The HOMO and LUMO energy gap that reflects the chemical activity of the molecule were also studied by DFT and above basis set. All theoretical results correspond to a great extent to experimental ones.

Symmetry properties of the electron density and following from it limits on the KS-DFT applications

NASA Astrophysics Data System (ADS)

Kaplan, Ilya G.

2018-03-01

At present, the Density Functional Theory (DFT) approach elaborated by Kohn with co-authors more than 50 years ago became the most widely used method for study molecules and solids. Using modern computation facilities, it can be applied to systems with million atoms. In the atmosphere of such great popularity, it is particularly important to know the limits of the applicability of DFT methods. In this report, I will discuss two cases when the conventional DFT approaches, using only electron density ρ and its gradients, cannot be applied (I will not consider the Ψ-versions of DFT). The first case is quite evident. In the degenerated states, the electron density may not be defined, since electronic and nuclear motions cannot be separated, the vibronic interaction mixed them. The second case is related to the spin of the state. As it was rigorously proved by group theoretical methods at the theorem level, the electron density does not depend on the total spin S of the arbitrary N-electron state. It means that the Kohn-Sham equations have the same form for states with different S. The critical survey of elaborated DFT procedures, taking into account spin, shows that they modified only exchange functionals, the correlation functionals do not correspond to the spin of the state. The point is that the conception of spin cannot be defined in the framework of the electron density formalism, which corresponds to the one-particle reduced density matrix. This is the main reason of the problems arising in the study by DFT of magnetic properties of the transition metals. The possible way of resolving these problems can be found in the two-particle reduced density matrix formulation of DFT.

Application of Koopmans' theorem for density functional theory to full valence-band photoemission spectroscopy modeling.

PubMed

Li, Tsung-Lung; Lu, Wen-Cai

2015-10-05

In this work, Koopmans' theorem for Kohn-Sham density functional theory (KS-DFT) is applied to the photoemission spectra (PES) modeling over the entire valence-band. To examine the validity of this application, a PES modeling scheme is developed to facilitate a full valence-band comparison of theoretical PES spectra with experiments. The PES model incorporates the variations of electron ionization cross-sections over atomic orbitals and a linear dispersion of spectral broadening widths. KS-DFT simulations of pristine rubrene (5,6,11,12-tetraphenyltetracene) and potassium-rubrene complex are performed, and the simulation results are used as the input to the PES models. Two conclusions are reached. First, decompositions of the theoretical total spectra show that the dissociated electron of the potassium mainly remains on the backbone and has little effect on the electronic structures of phenyl side groups. This and other electronic-structure results deduced from the spectral decompositions have been qualitatively obtained with the anionic approximation to potassium-rubrene complexes. The qualitative validity of the anionic approximation is thus verified. Second, comparison of the theoretical PES with the experiments shows that the full-scale simulations combined with the PES modeling methods greatly enhance the agreement on spectral shapes over the anionic approximation. This agreement of the theoretical PES spectra with the experiments over the full valence-band can be regarded, to some extent, as a collective validation of the application of Koopmans' theorem for KS-DFT to valence-band PES, at least, for this hydrocarbon and its alkali-adsorbed complex. Copyright © 2015 Elsevier B.V. All rights reserved.

DFT calculations of electronic and optical properties of SrS with LDA, GGA and mGGA functionals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Shatendra, E-mail: shatendra@gmai.com; Sharma, Jyotsna; Sharma, Yogita

2016-05-06

The theoretical investigations of electronic and optical properties of SrS are made using the first principle DFT calculations. The calculations are performed for the local-density approximation (LDA), generalized gradient approximation (GGA) and for an alternative form of GGA i.e. metaGGA for both rock salt type (B1, Fm3m) and cesium chloride (B2, Pm3m) structures. The band structure, density of states and optical spectra are calculated under various available functional. The calculations with LDA and GGA functional underestimate the values of band gaps with all functional, however the values with mGGA show reasonably good agreement with experimental and those calculated by usingmore » other methods.« less

Adsorbate Diffusion on Transition Metal Nanoparticles

DTIC Science & Technology

2015-01-01

different sizes and shapes using density functional theory calculations. We show that nanoparticles bind adsorbates more strongly than the...structure theoretical methods, a quantitative study with accurate density functional theory (DFT) calculations is still missing. Here, we perform a...functional theory . The projector augmented wave (PAW) potentials29,30 were used for electron- ion interactions and the generalized gradient approximation

FT-IR and Raman vibrational analysis, B3LYP and M06-2X simulations of 4-bromomethyl-6-tert-butyl-2H-chromen-2-one

NASA Astrophysics Data System (ADS)

Sert, Yusuf; Puttaraju, K. B.; Keskinoğlu, Sema; Shivashankar, K.; Ucun, Fatih

2015-01-01

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized bacteriostatic and anti-tumor molecule namely, 4-bromomethyl-6-tert-butyl-2H-chromen-2-one have been investigated. The experimental FT-IR (4000-400 cm-1) and Raman spectra (4000-100 cm-1) of the compound in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parametrized, empirical exchange correlation function) with 6-311++G(d, p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations.

Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures

PubMed Central

Drummond, N. D.; Monserrat, Bartomeu; Lloyd-Williams, Jonathan H.; Ríos, P. López; Pickard, Chris J.; Needs, R. J.

2015-01-01

Establishing the phase diagram of hydrogen is a major challenge for experimental and theoretical physics. Experiment alone cannot establish the atomic structure of solid hydrogen at high pressure, because hydrogen scatters X-rays only weakly. Instead, our understanding of the atomic structure is largely based on density functional theory (DFT). By comparing Raman spectra for low-energy structures found in DFT searches with experimental spectra, candidate atomic structures have been identified for each experimentally observed phase. Unfortunately, DFT predicts a metallic structure to be energetically favoured at a broad range of pressures up to 400 GPa, where it is known experimentally that hydrogen is non-metallic. Here we show that more advanced theoretical methods (diffusion quantum Monte Carlo calculations) find the metallic structure to be uncompetitive, and predict a phase diagram in reasonable agreement with experiment. This greatly strengthens the claim that the candidate atomic structures accurately model the experimentally observed phases. PMID:26215251

Electronic properties of Laves phase ZrFe{sub 2} using Compton spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhatt, Samir, E-mail: sameerbhatto11@gmail.com; Kumar, Kishor; Ahuja, B. L.

First-ever experimental Compton profile of Laves phase ZrFe{sub 2}, using indigenous 20 Ci {sup 137}Cs Compton spectrometer, is presented. To analyze the experimental electron momentum density, we have deduced the theoretical Compton profiles using density functional theory (DFT) and hybridization of DFT and Hartree-Fock scheme within linear combination of atomic orbitals (LCAO) method. The energy bands and density of states are also calculated using LCAO prescription. The theoretical profile based on local density approximation gives a better agreement with the experimental profile than other reported schemes. The present investigations validate the inclusion of correlation potential of Perdew-Zunger in predicting themore » electronic properties of ZrFe{sub 2}.« less

Ab initio calculations of the electronic structure and specific optical features of β-LiNH4SO4 single crystals

NASA Astrophysics Data System (ADS)

Rudysh, M. Ya.; Brik, M. G.; Stadnyk, V. Yo.; Brezvin, R. S.; Shchepanskyi, P. A.; Fedorchuk, A.; Khyzhun, O. Y.; Kityk, I. V.; Piasecki, M.

2018-01-01

In the present work complex experimental and theoretical studies of electronic and optical properties for β-lithium-ammonium sulfate crystals of good optical quality are performed using the X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). Standard immersion and spectroscopic techniques accompanied by the theoretical quantum-chemical calculations in the density functional theory (DFT) framework were applied. Calculations of band structure and related properties were carried out within a framework of local density and generalized gradient approximations as well as hybrid B3LYP functionals. The energy levels features and their origin are established from the DFT calculations and they were ferified by XPS and XES measurements. Theoretical and experimental refractive indices dispersions along the principal crystallographic directions (nx, ny and nz) as well as birefringence dispersion (Δnx, Δny and Δnz) in the visible spectral range are obtained. It was found a closeness of nx and ny curves for the titled crystals. More precise birefringence examining predicts their intersection at λ ≈ 190 nm.

Exchange coupling and magnetic anisotropy of exchanged-biased quantum tunnelling single-molecule magnet Ni3Mn2 complexes using theoretical methods based on Density Functional Theory.

PubMed

Gómez-Coca, Silvia; Ruiz, Eliseo

2012-03-07

The magnetic properties of a new family of single-molecule magnet Ni(3)Mn(2) complexes were studied using theoretical methods based on Density Functional Theory (DFT). The first part of this study is devoted to analysing the exchange coupling constants, focusing on the intramolecular as well as the intermolecular interactions. The calculated intramolecular J values were in excellent agreement with the experimental data, which show that all the couplings are ferromagnetic, leading to an S = 7 ground state. The intermolecular interactions were investigated because the two complexes studied do not show tunnelling at zero magnetic field. Usually, this exchange-biased quantum tunnelling is attributed to the presence of intermolecular interactions calculated with the help of theoretical methods. The results indicate the presence of weak intermolecular antiferromagnetic couplings that cannot explain the ferromagnetic value found experimentally for one of the systems. In the second part, the goal is to analyse magnetic anisotropy through the calculation of the zero-field splitting parameters (D and E), using DFT methods including the spin-orbit effect.

Exciton Localization and Optical Emission in Aryl-Functionalized Carbon Nanotubes

DOE PAGES

Gifford, Brendan Joel; Kilina, Svetlana; Htoon, Han; ...

2017-10-26

Recent spectroscopic studies have revealed the appearance of multiple low-energy peaks in the fluorescence of single-walled carbon nanotubes (SWCNTs) upon their covalent functionalization by aryl groups. The photophysical nature of these low energy optical bands is of significant interest in the quest to understand their appearance and to achieve their precise control via chemical modification of SWCNTs. This theoretical study explains the specific energy dependence of emission features introduced in chemically functionalized (6,5) SWCNTs with aryl bromides at different conformations and in various dielectric media. Calculations using density functional theory (DFT) and time dependent DFT (TD-DFT) show that the specificmore » isomer geometry—the relative position of functional groups on the carbon-ring of the nanotube—is critical for controlling the energies and intensities of optical transitions introduced by functionalization, while the dielectric environment and the chemical composition of functional groups play less significant roles. Furthermore, the predominant effects on optical properties as a result of functionalization conformation are rationalized by exciton localization on the surface of the SWCNT near the dopant sp3-defect but not onto the functional group itself.« less

DFT/TD-DFT study of solvent effect as well the substituents influence on the different features of TPP derivatives for PDT application

NASA Astrophysics Data System (ADS)

Dulski, Mateusz; Kempa, Marta; Kozub, Patrycja; Wójcik, Justyna; Rojkiewicz, Marcin; Kuś, Piotr; Szurko, Agnieszka; Ratuszna, Alicja; Wrzalik, Roman

2013-03-01

Spectral characteristics study of meso-tetraphenylporphyrin derivatives (TPP1 and TPP2) used as photosensitizers for utilization in photodynamic therapy (PDT) has been performed by density functional theory (DFT) and time dependent DFT (TD-DFT) calculations at B3LYP/6-31G(d) level of theory using PCM solvation model. The geometrical parameters of porphyrins have been studied for ground and excited-state geometry to deduce the influence of various substituents as well as solvent effect on the deformation of porphyrin ring. Two theoretical approaches - linear response (LR) and external iteration (EI) - have been performed to replicate absorption and fluorescence emission spectra. Experimental and theoretical investigations have shown that EI method reproduces the absorption energies very well for both singlet-singlet and triplet-triplet transitions, whereas the LR approach is more coherent with experimental fluorescence emission spectra. Spectral features and HOMO-LUMO band gap analysis have shown that TPP1 can be more useful in PDT. Calculations have revealed that two the highest occupied and two the lowest unoccupied molecular orbitals are responsible for the Q-band absorption and are located mainly on the porphyrin ring. In order to verify the substituent effect on the activity of tested compounds in their ground and excited states, the molecular electrostatic potential surfaces have been analyzed.

Theoretical investigation of cyromazine tautomerism using density functional theory and Møller–Plesset perturbation theory methods

USDA-ARS?s Scientific Manuscript database

A computational chemistry analysis of six unique tautomers of cyromazine, a pesticide used for fly control, was performed with density functional theory (DFT) and canonical second order Møller–Plesset perturbation theory (MP2) methods to gain insight into the contributions of molecular structure to ...

Theoretical Developments in Decision Field Theory: Comment on Tsetsos, Usher, and Chater (2010)

ERIC Educational Resources Information Center

Hotaling, Jared M.; Busemeyer, Jerome R.; Li, Jiyun

2010-01-01

Tsetsos, Usher, and Chater (2010) presented several criticisms of decision field theory (DFT) involving its distance function, instability under externally controlled stopping times, and lack of robustness to various multialternative choice scenarios. Here, we counter those claims with a specification of a distance function based on the…

Pressure-induced Lifshitz transition in NbP: Raman, x-ray diffraction, electrical transport, and density functional theory

NASA Astrophysics Data System (ADS)

Gupta, Satyendra Nath; Singh, Anjali; Pal, Koushik; Muthu, D. V. S.; Shekhar, C.; Qi, Yanpeng; Naumov, Pavel G.; Medvedev, Sergey A.; Felser, C.; Waghmare, U. V.; Sood, A. K.

2018-02-01

We report high-pressure Raman, synchrotron x-ray diffraction, and electrical transport studies on Weyl semimetals NbP and TaP along with first-principles density functional theoretical (DFT) analysis. The frequencies of first-order Raman modes of NbP harden with increasing pressure and exhibit a slope change at Pc˜9 GPa. The pressure-dependent resistivity exhibits a minimum at Pc. The temperature coefficient of resistivity below Pc is positive as expected for semimetals but changes significantly in the high-pressure phase. Using DFT calculations, we show that these anomalies are associated with a pressure-induced Lifshitz transition, which involves the appearance of electron and hole pockets in its electronic structure. In contrast, the results of Raman and synchrotron x-ray diffraction experiments on TaP and DFT calculations show that TaP is quite robust under pressure and does not undergo any phase transition.

Combined spectroscopic, DFT, TD-DFT and MD study of newly synthesized thiourea derivative

NASA Astrophysics Data System (ADS)

Menon, Vidya V.; Sheena Mary, Y.; Shyma Mary, Y.; Panicker, C. Yohannan; Bielenica, Anna; Armaković, Stevan; Armaković, Sanja J.; Van Alsenoy, Christian

2018-03-01

A novel thiourea derivative, 1-(3-bromophenyl)-3-[3-(trifluoromethyl)phenyl]thiourea (ANF-22) is synthesized and characterized by FTIR, FT-Raman and NMR spectroscopy experimentally and theoretically. A detailed conformational analysis of the title molecule has been conducted in order to locate the lowest energy geometry, which was further subjected to the detailed investigation of spectroscopic, reactive, degradation and docking studies by density functional theory (DFT) calculations and molecular dynamics (MD) simulations. Time dependent DFT (TD-DFT) calculations have been used also in order to simulate UV spectra and investigate charge transfer within molecule. Natural bond orbital analysis has been performed analyzing the charge delocalization and using HOMO and LUMO energies the electronic properties are analyzed. Molecular electrostatic potential map is used for the quantitative measurement of active sites in the molecule. In order to determine the locations possibly prone to electrophilic attacks we have calculated average local ionization energies and mapped them to the electron density surface. Further insight into the local reactivity properties have been obtained by calculation of Fukui functions, also mapped to the electron density surface. Possible degradation properties by the autoxidation mechanism have been assessed by calculations of bond dissociation energies for hydrogen abstraction. Atoms of title molecule with significant interactions with water molecules have been determined by calculations of radial distribution functions. The title compound can be a lead compound for developing new analgesic drug.

Study of electronic structure and Compton profiles of transition metal diborides

NASA Astrophysics Data System (ADS)

Bhatt, Samir; Heda, N. L.; Kumar, Kishor; Ahuja, B. L.

2017-08-01

We report Compton profiles (CPs) of transition metal diborides (MB2; M= Ti and Zr) using a 740 GBq 137Cs Compton spectrometer measured at an intermediate resolution of 0.34 a.u. To validate the experimental momentum densities, we have employed the linear combination of atomic orbitals (LCAO) method to compute the theoretical CPs along with the energy bands, density of states (DOS) and Mulliken's population response. The LCAO computations have been performed in the frame work of density functional theory (DFT) and hybridization of Hartree-Fock and DFT (namely B3LYP and PBE0). For both the diborides, the CPs based on revised Perdew-Burke-Ernzerhof exchange and correlation functions (DFT-PBESol) lead to a better agreement with the experimental momentum densities than other reported approximations. Energy bands, DOS and real space analysis of CPs confirm a metallic-like character of both the borides. Further, a comparison of DFT-PBESol and experimental data on equal-valence-electron-density scale shows more ionicity in ZrB2 than that in TiB2, which is also supported by the Mulliken's population based charge transfer data.

Uncertainty quantification and propagation in nuclear density functional theory

DOE PAGES

Schunck, N.; McDonnell, J. D.; Higdon, D.; ...

2015-12-23

Nuclear density functional theory (DFT) is one of the main theoretical tools used to study the properties of heavy and superheavy elements, or to describe the structure of nuclei far from stability. While on-going eff orts seek to better root nuclear DFT in the theory of nuclear forces, energy functionals remain semi-phenomenological constructions that depend on a set of parameters adjusted to experimental data in fi nite nuclei. In this study, we review recent eff orts to quantify the related uncertainties, and propagate them to model predictions. In particular, we cover the topics of parameter estimation for inverse problems, statisticalmore » analysis of model uncertainties and Bayesian inference methods. Illustrative examples are taken from the literature.« less

The influence of anharmonic and solvent effects on the theoretical vibrational spectra of the guanine-cytosine base pairs in Watson-Crick and Hoogsteen configurations.

PubMed

Bende, Attila; Muntean, Cristina M

2014-03-01

The theoretical IR and Raman spectra of the guanine-cytosine DNA base pairs in Watson-Crick and Hoogsteen configurations were computed using DFT method with M06-2X meta-hybrid GGA exchange-correlation functional, including the anharmonic corrections and solvent effects. The results for harmonic frequencies and their anharmonic corrections were compared with our previously calculated values obtained with the B3PW91 hybrid GGA functional. Significant differences were obtained for the anharmonic corrections calculated with the two different DFT functionals, especially for the stretching modes, while the corresponding harmonic frequencies did not differ considerable. For the Hoogtseen case the H⁺ vibration between the G-C base pair can be characterized as an asymmetric Duffing oscillator and therefore unrealistic anharmonic corrections for normal modes where this proton vibration is involved have been obtained. The spectral modification due to the anharmonic corrections, solvent effects and the influence of sugar-phosphate group for the Watson-Crick and Hoogsteen base pair configurations, respectively, were also discussed. For the Watson-Crick case also the influence of the stacking interaction on the theoretical IR and Raman spectra was analyzed. Including the anharmonic correction in our normal mode analysis is essential if one wants to obtain correct assignments of the theoretical frequency values as compared with the experimental spectra.

BH-DFTB/DFT calculations for iron clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aktürk, Abdurrahman; Sebetci, Ali, E-mail: asebetci@mevlana.edu.tr

2016-05-15

We present a study on the structural, electronic, and magnetic properties of Fe{sub n}(n  =  2  −  20) clusters by performing density functional tight binding (DFTB) calculations within a basin hopping (BH) global optimization search followed by density functional theory (DFT) investigations. The structures, total energies and total spin magnetic moments are calculated and compared with previously reported theoretical and experimental results. Two basis sets SDD with ECP and 6-31G** are employed in the DFT calculations together with BLYP GGA exchange-correlation functional. The results indicate that the offered BH-DFTB/DFT strategy collects all the global minima of which different minima havemore » been reported in the previous studies by different groups. Small Fe clusters have three kinds of packing; icosahedral (Fe{sub 9−13}), centered hexagonal antiprism (Fe{sub 14−17}, Fe{sub 20}), and truncated decahedral (Fe{sub 17(2)}, Fe{sub 18−19}). It is obtained in a qualitative agreement with the time of flight mass spectra that the magic numbers for the small Fe clusters are 7, 13, 15, and 19 and with the collision induced dissociation experiments that the sizes 6, 7, 13, 15, and 19 are thermodynamically more stable than their neighboring sizes. The spin magnetic moment per atom of Fe{sub n}(n = 2 − 20) clusters is between 2.4 and 3.6 μ{sub B} for the most of the sizes. The antiferromagnetic coupling between the central and the surface atoms of the Fe{sub 13} icosahedron, which have already been reported by experimental and theoretical studies, is verified by our calculations as well. The quantitative disagreements between the calculations and measurements of the magnetic moments of the individual sizes are still to be resolved.« less

Molecular structure, vibrational spectral assignments (FT-IR and FT-RAMAN), NMR, NBO, HOMO-LUMO and NLO properties of O-methoxybenzaldehyde based on DFT calculations

NASA Astrophysics Data System (ADS)

Vennila, P.; Govindaraju, M.; Venkatesh, G.; Kamal, C.

2016-05-01

Fourier transform - Infra red (FT-IR) and Fourier transform - Raman (FT-Raman) spectroscopic techniques have been carried out to analyze O-methoxy benzaldehyde (OMB) molecule. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT). The vibrational analysis of stable isomer of OMB has been carried out by FT-IR and FT-Raman in combination with theoretical method simultaneously. The first-order hyperpolarizability and the anisotropy polarizability invariant were computed by DFT method. The atomic charges, hardness, softness, ionization potential, electronegativity, HOMO-LUMO energies, and electrophilicity index have been calculated. The 13C and 1H Nuclear magnetic resonance (NMR) have also been obtained by GIAO method. Molecular electronic potential (MEP) has been calculated by the DFT calculation method. Electronic excitation energies, oscillator strength and excited states characteristics were computed by the closed-shell singlet calculation method.

Theoretical and experimental prediction of the redox potentials of metallocene compounds

NASA Astrophysics Data System (ADS)

Li, Ya-Ping; Liu, Hai-Bo; Liu, Tao; Yu, Zhang-Yu

2017-11-01

The standard redox electrode potential ( E°) values of metallocene compounds are obtained theoretically with density functional theory (DFT) method at B3LYP/6-311++G( d, p) level and experimentally with cyclic voltammetry (CV). The theoretical E° values of metallocene compounds are in good agreement with experimental ones. We investigate the substituent effects on the redox properties of metallocene compounds. Among the four metallocene compounds, the E° values is largest for titanocene dichloride and smallest for ferrocene.

NEGF-DFT characterization of diarylethene photoswitches: Impact of substituents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Dyck, Colin; Geskin, Victor; Cornil, Jérôme

2015-01-22

In this presentation we report a theoretical study on the performance of diarylethene photoswitches. We start with a comparison between the electronic structures of different substituted diarylethene cores. Using a NEGF-DFT formalism we compute self-consistently transmission and IV curves with a focus on the impact of the substituents usually introduced for various synthetic and functional reasons. We find that the conductance properties of the diarylethene photoswitches are rather insensitive to these substitutions in the core. In the interpretation of our results, we make a connection between transmission spectra and molecular electronic properties.

A theoretical insight for solvent effect on myoglobin assay of W(CO)4L2 type novel complexes with DFT/TDDFT

NASA Astrophysics Data System (ADS)

Üstün, Elvan; Demi˙r, Serpil; Coşkun, Feyzullah; Kaloğlu, Murat; Şahi˙n, Onur; Büyükgüngör, Orhan; Özdemi˙r, İsmail

2016-11-01

Novel tetracarbonyl complexes of type W(CO)4L2 (L: 4-chlorobenzylimidazoline; 4-methylbenzylimidazoline; 3,5-dimethylbenzylimidazoline; 2,4,6-trimethylbenzylimidazoline; 2,3,5,6- tetramethylbenzylimidazoline) were synthesized. Then newly synthesized novel compounds were characterized by IR, 1H NMR, 13C NMR and LC-MS. The characterizations of two of the complexes have also been confirmed with single crystal X-Ray diffraction and DFT optimization results of these complexes have been compared with single crystal results. We have investigated the solvent effect on the structure and metal-to-ligand charge transfer (MLCT) transitions with DFT/TDDFT calculations with ORCA package program with BP86 functional.

Developing Dynamic Field Theory Architectures for Embodied Cognitive Systems with cedar.

PubMed

Lomp, Oliver; Richter, Mathis; Zibner, Stephan K U; Schöner, Gregor

2016-01-01

Embodied artificial cognitive systems, such as autonomous robots or intelligent observers, connect cognitive processes to sensory and effector systems in real time. Prime candidates for such embodied intelligence are neurally inspired architectures. While components such as forward neural networks are well established, designing pervasively autonomous neural architectures remains a challenge. This includes the problem of tuning the parameters of such architectures so that they deliver specified functionality under variable environmental conditions and retain these functions as the architectures are expanded. The scaling and autonomy problems are solved, in part, by dynamic field theory (DFT), a theoretical framework for the neural grounding of sensorimotor and cognitive processes. In this paper, we address how to efficiently build DFT architectures that control embodied agents and how to tune their parameters so that the desired cognitive functions emerge while such agents are situated in real environments. In DFT architectures, dynamic neural fields or nodes are assigned dynamic regimes, that is, attractor states and their instabilities, from which cognitive function emerges. Tuning thus amounts to determining values of the dynamic parameters for which the components of a DFT architecture are in the specified dynamic regime under the appropriate environmental conditions. The process of tuning is facilitated by the software framework cedar , which provides a graphical interface to build and execute DFT architectures. It enables to change dynamic parameters online and visualize the activation states of any component while the agent is receiving sensory inputs in real time. Using a simple example, we take the reader through the workflow of conceiving of DFT architectures, implementing them on embodied agents, tuning their parameters, and assessing performance while the system is coupled to real sensory inputs.

Developing Dynamic Field Theory Architectures for Embodied Cognitive Systems with cedar

PubMed Central

Lomp, Oliver; Richter, Mathis; Zibner, Stephan K. U.; Schöner, Gregor

2016-01-01

Embodied artificial cognitive systems, such as autonomous robots or intelligent observers, connect cognitive processes to sensory and effector systems in real time. Prime candidates for such embodied intelligence are neurally inspired architectures. While components such as forward neural networks are well established, designing pervasively autonomous neural architectures remains a challenge. This includes the problem of tuning the parameters of such architectures so that they deliver specified functionality under variable environmental conditions and retain these functions as the architectures are expanded. The scaling and autonomy problems are solved, in part, by dynamic field theory (DFT), a theoretical framework for the neural grounding of sensorimotor and cognitive processes. In this paper, we address how to efficiently build DFT architectures that control embodied agents and how to tune their parameters so that the desired cognitive functions emerge while such agents are situated in real environments. In DFT architectures, dynamic neural fields or nodes are assigned dynamic regimes, that is, attractor states and their instabilities, from which cognitive function emerges. Tuning thus amounts to determining values of the dynamic parameters for which the components of a DFT architecture are in the specified dynamic regime under the appropriate environmental conditions. The process of tuning is facilitated by the software framework cedar, which provides a graphical interface to build and execute DFT architectures. It enables to change dynamic parameters online and visualize the activation states of any component while the agent is receiving sensory inputs in real time. Using a simple example, we take the reader through the workflow of conceiving of DFT architectures, implementing them on embodied agents, tuning their parameters, and assessing performance while the system is coupled to real sensory inputs. PMID:27853431

Vibrational spectroscopic study, charge transfer interaction and nonlinear optical properties of L-asparaginium picrate: a density functional theoretical approach.

PubMed

Elleuch, Nabil; Amamou, Walid; Ben Ahmed, Ali; Abid, Younes; Feki, Habib

2014-07-15

Single crystals of L-asparaginium picrate (LASP) were grown by slow evaporation technique at room temperature and were the subject of an X-ray powder diffraction study to confirm the crystalline nature of the synthesized compound. FT-IR and Raman spectra were recorded and analyzed with the aid of the density functional theory (DFT) calculations in order to make a suitable assignment of the observed bands. The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities and the first hyperpolarizability were investigated with the help of B3LYP method using 6-31G(d) basis set. The theoretical FT-IR and Raman spectra of LASP were simulated and compared with the experimental data. A good agreement was shown and a reliable vibrational assignment was made. Natural bond orbital (NBO) analysis was carried out to demonstrate the various inter and intramolecular interactions that are responsible for the stabilization of the title compound leading to high NLO activity. A study on the electronic properties was performed by time-dependent DFT (TD-DFT) approach. The lowering in the HOMO and LUMO energy gap explains the eventual charge transfer interactions that take place within the molecules. Copyright © 2014 Elsevier B.V. All rights reserved.

DFT study of IR and Raman spectra of phosphotrihydrazone dendrimer with terminal phenolic groups

NASA Astrophysics Data System (ADS)

Furer, V. L.; Vandyukov, A. E.; Majoral, J. P.; Caminade, A. M.; Kovalenko, V. I.

2017-09-01

FT Raman and infrared spectra of phosphotrihydrazone (S)P[N(CH3)Ndbnd CHsbnd C6H4sbnd OH]3 (G0) were recorded. This compound is a zero generation phosphorus dendrimer with terminal phenolic groups. Optimal geometry and vibrational frequencies were calculated for G0 using the density functional theory (DFT). The molecule studied has C3 symmetry. In the molecule G0, each sbnd C6H4sbnd CHdbnd Nsbnd N(CH3)sbnd P arm is flat. Optimized geometric parameters correspond to experimental data. The core of the dendrimer manifests itself as a band at 647 cm-1 in the Raman spectrum of G0 related to Pdbnd S stretching. Phenolic end functions exhibit a well-defined band at 3374 cm-1 in the experimental IR spectrum of G0. The observed frequency of the OH stretching vibrations of the phenolic groups is lower than the theoretical value due to the intermolecular Osbnd H⋯O hydrogen bond. This hydrogen bond is also responsible for the higher intensity of this band in the experimental IR spectrum compared with the theoretical value. DFT calculations suggest full assignment of normal modes. Global and local descriptors characterize the reactivity of the core and end groups.

The biomolecule, 2-[(2-methoxyl)sulfanyl]-4-(2-methylpropyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile: FT-IR, Laser-Raman spectra and DFT

NASA Astrophysics Data System (ADS)

Sert, Yusuf; El-Emam, Ali A.; Al-Deeb, Omar A.; Al-Turkistani, Abdulghafoor A.; Ucun, Fatih; Çırak, Çağrı

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized potential chemotherapeutic agent namely, 2-[(2-methoxyl)sulfanyl]-4-(2-methylpropyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile have been investigated. The experimental FT-IR (4000-400 cm-1) and Laser-Raman spectra (4000-100 cm-1) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with the results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations.

FT-IR, Laser-Raman spectra and computational analysis of 5-Methyl-3-phenylisoxazole-4-carboxylic acid.

PubMed

Sert, Yusuf; Mahendra, M; Keskinoğlu, S; Chandra; Srikantamurthy, N; Umesha, K B; Çırak, Ç

2015-03-15

In this study the experimental and theoretical vibrational frequencies of a newly synthesized anti-tumor, antiviral, hypoglycemic, antifungal and anti-HIV agent namely, 5-Methyl-3-phenylisoxazole-4-carboxylic acid has been investigated. The experimental FT-IR (4000-400 cm(-1)) and Laser-Raman spectra (4000-100 cm(-1)) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths, bond angles and torsion angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parametrized, empirical exchange correlation function) with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated by using the same theoretical calculations. Copyright © 2014 Elsevier B.V. All rights reserved.

FT-IR, Laser-Raman spectra and computational analysis of 5-Methyl-3-phenylisoxazole-4-carboxylic acid

NASA Astrophysics Data System (ADS)

Sert, Yusuf; Mahendra, M.; Keskinoğlu, S.; Chandra; Srikantamurthy, N.; Umesha, K. B.; Çırak, Ç.

2015-03-01

In this study the experimental and theoretical vibrational frequencies of a newly synthesized anti-tumor, antiviral, hypoglycemic, antifungal and anti-HIV agent namely, 5-Methyl-3-phenylisoxazole-4-carboxylic acid has been investigated. The experimental FT-IR (4000-400 cm-1) and Laser-Raman spectra (4000-100 cm-1) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths, bond angles and torsion angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parametrized, empirical exchange correlation function) with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated by using the same theoretical calculations.

Use of vibrational spectroscopy to study 4-benzyl-3-(thiophen-2-yl)-4,5-dihydro-1H-1,2,4-triazole-5-thione: A combined theoretical and experimental approach

NASA Astrophysics Data System (ADS)

Sert, Yusuf; El-Emam, Ali A.; Al-Abdullah, Ebtehal S.; Al-Tamimi, Abdul-Malek S.; Çırak, Çağrı; Ucun, Fatih

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized potential anti-inflammatory agent namely, 4-benzyl-3-(thiophen-2-yl)-4,5-dihydro-1H-1,2,4-triazole-5-thione have been investigated. The experimental FT-IR (4000-400 cm-1) and Laser-Raman spectra (4000-100 cm-1) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and the optimized geometric parameters (bond lengths, bond angles and dihedral angles) have been calculated using density functional theory methods (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: the highly parameterized, empirical exchange correlation function) with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis using VEDA 4 software program. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations.

Use of vibrational spectroscopy to study 4-benzyl-3-(thiophen-2-yl)-4,5-dihydro-1H-1,2,4-triazole-5-thione: A combined theoretical and experimental approach.

PubMed

Sert, Yusuf; El-Emam, Ali A; Al-Abdullah, Ebtehal S; Al-Tamimi, Abdul-Malek S; Cırak, Cağrı; Ucun, Fatih

2014-05-21

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized potential anti-inflammatory agent namely, 4-benzyl-3-(thiophen-2-yl)-4,5-dihydro-1H-1,2,4-triazole-5-thione have been investigated. The experimental FT-IR (4000-400cm(-1)) and Laser-Raman spectra (4000-100cm(-1)) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and the optimized geometric parameters (bond lengths, bond angles and dihedral angles) have been calculated using density functional theory methods (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: the highly parameterized, empirical exchange correlation function) with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis using VEDA 4 software program. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data and results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations. Copyright © 2014 Elsevier B.V. All rights reserved.

Binding of urea and thiourea with a barbiturate derivative: experimental and theoretical approach.

PubMed

Dixit, Namrata; Shukla, P K; Mishra, P C; Mishra, Lallan; Roesky, Herbert W

2010-01-14

A barbiturate derivative [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]-2H-chromeno[2,3-d] pyrimidine-2,4(3H)-dione)] (L1) possesses functionalities complementary to amide and thioamide. Hence its binding with urea and thiourea, is monitored using UV-vis and fluorescence titrations as well as isothermal titration calorimetry (ITC) study. Theoretical studies on hydrogen-bonded complexes of L1-urea and L1-thiourea in the gas phase, aqueous, and DMSO medium are carried out using density functional theory (DFT) at the B3LYP/6-31G** level. The theoretical calculations support the experimental results.

Combine experimental and theoretical investigation on an alkaloid-Dimethylisoborreverine

NASA Astrophysics Data System (ADS)

Singh, Swapnil; Singh, Harshita; Karthick, T.; Agarwal, Parag; Erande, Rohan D.; Dethe, Dattatraya H.; Tandon, Poonam

2016-01-01

A combined experimental (FT-IR, 1H and 13C NMR) and theoretical approach is used to study the structure and properties of antimalarial drug dimethylisoborreverine (DMIB). Conformational analysis, has been performed by plotting one dimensional potential energy curve that was computed using density functional theory (DFT) with B3LYP/6-31G method and predicted conformer A1 as the most stable conformer. After full geometry optimization, harmonic wavenumbers were computed for conformer A1 at the DFT/B3LYP/6-311++G(d,P) level. A complete vibrational assignment of all the vibrational modes have been performed on the bases of the potential energy distribution (PED) and theoretical results were found to be in good agreement with the observed data. To predict the solvent effect, the UV-Vis spectra were calculated in different solvents by polarizable continuum model using TD-DFT method. Molecular docking studies were performed to test the biological activity of the sample using SWISSDOCK web server and Hex 8.0.0 software. The molecular electrostatic potential (MESP) was plotted to identify the reactive sites of the molecule. Natural bond orbital (NBO) analysis was performed to get a deep insight of intramolecular charge transfer. Thermodynamical parameters were calculated to predict the direction of chemical reaction.

Theoretical Analysis of Optical Absorption and Emission in Mixed Noble Metal Nanoclusters.

PubMed

Day, Paul N; Pachter, Ruth; Nguyen, Kiet A

2018-04-26

In this work, we studied theoretically two hybrid gold-silver clusters, which were reported to have dual-band emission, using density functional theory (DFT) and linear and quadratic response time-dependent DFT (TDDFT). Hybrid functionals were found to successfully predict absorption and emission, although explanation of the NIR emission from the larger cluster (cluster 1) requires significant vibrational excitation in the final state. For the smaller cluster (cluster 2), the Δ H(0-0) value calculated for the T1 → S0 transition, using the PBE0 functional, is in good agreement with the measured NIR emission, and the calculated T2 → S0 value is in fair agreement with the measured visible emission. The calculated T1 → S0 phosphorescence Δ H(0-0) for cluster 1 is close to the measured visible emission energy. In order for the calculated phosphorescence for cluster 1 to agree with the intense NIR emission reported experimentally, the vibrational energy of the final state (S0) is required to be about 0.7 eV greater than the zero-point vibrational energy.

Theoretical Characterization of Visual Signatures and Calculation of Approximate Global Harmonic Frequency Scaling Factors

NASA Astrophysics Data System (ADS)

Kashinski, D. O.; Nelson, R. G.; Chase, G. M.; di Nallo, O. E.; Byrd, E. F. C.

2016-05-01

We are investigating the accuracy of theoretical models used to predict the visible, ultraviolet, and infrared spectra, as well as other properties, of product materials ejected from the muzzle of currently fielded systems. Recent advances in solid propellants has made the management of muzzle signature (flash) a principle issue in weapons development across the calibers. A priori prediction of the electromagnetic spectra of formulations will allow researchers to tailor blends that yield desired signatures and determine spectrographic detection ranges. Quantum chemistry methods at various levels of sophistication have been employed to optimize molecular geometries, compute unscaled harmonic frequencies, and determine the optical spectra of specific gas-phase species. Electronic excitations are being computed using Time Dependent Density Functional Theory (TD-DFT). Calculation of approximate global harmonic frequency scaling factors for specific DFT functionals is also in progress. A full statistical analysis and reliability assessment of computational results is currently underway. Work supported by the ARL, DoD-HPCMP, and USMA.

Spectroscopic and vibrational analysis of the methoxypsoralen system: A comparative experimental and theoretical study

NASA Astrophysics Data System (ADS)

Liu, Y.; Yuan, H.; Vo-Dinh, T.

2013-03-01

Raman spectra measurements and density functional theory (DFT) calculations were performed to investigate three psoralens: 5-amino-8-methoxypsoralen (5-A-8-MOP), 5-methoxypsoralen (5-MOP) and 8-methoxypsoralen (8-MOP) with the aim of differentiating these similar bioactive molecules. The Raman spectra were recorded in the region 300-3500 cm-1. All three psoralens were found to have similar Raman spectrum in the region 1500-1650 cm-1. 5-A-8-MOP can be easily differentiated from 5-MOP or 8-MOP based on the Raman spectrum. The Raman spectrum differences at 651 and 795 cm-1 can be used to identify 5-MOP from 8-MOP. The theoretically computed vibrational frequencies and relative peak intensities were compared with experimental data. DFT calculations using the B3LYP method and 6-311++G(d,p) basis set were found to yield results that are very comparable to experimental Raman spectra. Detailed vibrational assignments were performed with DFT calculations and the potential energy distribution (PED) obtained from the Vibrational Energy Distribution Analysis (VEDA) program.

Structural characterization, surface characteristics and non covalent interactions of a heterocyclic Schiff base: Evaluation of antioxidant potential by UV-visible spectroscopy and DFT

NASA Astrophysics Data System (ADS)

Chithiraikumar, S.; Gandhimathi, S.; Neelakantan, M. A.

2017-06-01

A heterocyclic Schiff base, (E)-4-(1-((pyridin-2-ylmethyl)imino)ethyl)benzene-1,3-diol (L) was synthesized and isolated as single crystals. Its structure was characterized by FT-IR, UV, 1H and 13C NMR, and further confirmed by X-ray crystallography. Qualitatively and quantitatively the various interactions in the crystal structure of L has been analyzed by Hirshfeld surfaces and 2D fingerprint plots. Non covalent interactions have been studied by electron localization function (ELF) and mapped with reduced density gradient (RDG) analysis. The molecular structure was studied computationally by DFT-B3LYP/6-311G(d,p) calculations. HOMO-LUMO energy levels, chemical reactivity descriptors and thermodynamic parameters have been investigated at the same level of theory. The antioxidant potential of L was evaluated experimentally by measuring DPPH free radical scavenging effect using UV-visible spectroscopy and theoretically by DFT. Theoretical parameters, such as bond dissociation enthalpy (BDE) and spin density calculated suggests that antioxidant potential of L is due to H atom abstraction from the sbnd OH group.

Fullerene Cyanation Does Not Always Increase Electron Affinity: Experimental and Theoretical Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clikeman, Tyler T.; Deng, Shihu; Popov, Alexey A.

2015-01-01

The electron affinities of C70 derivatives with trifluoromethyl, methyl and cyano groups were studied experimentally and theoretically using low-temperature photoelectron spectroscopy (LT PES) and density functional theory (DFT). The electronic effects of these functional groups were determined and found to be highly dependent on the addition patterns. Substitution of CF3 for CN for the same addition pattern increases the experimental electron affinity by 70 meV per substitution. The synthesis of a new fullerene derivative, C70(CF3)10(CN)2, is reported for the first time

An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

NASA Astrophysics Data System (ADS)

Hendrickson, Heidi Phillips

A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their technological design and development. Time dependent perturbation theory, employed by non-equilibrium Green's function formalism, is utilized to study the effect of quantum coherences on electron transport and the effect of symmetry breaking on the electronic spectra of model molecular junctions. The fourth part of this thesis presents the design of a physical chemistry course based on a pedagogical approach called Writing-to-Teach. The nature of inaccuracies expressed in student-generated explanations of quantum chemistry topics, and the ability of a peer review process to engage these inaccuracies, is explored within this context.

A study of isotropic-nematic transition of quadrupolar Gay-Berne fluid using density-functional theory approach

NASA Astrophysics Data System (ADS)

Singh, Ram Chandra; Ram, Jokhan

2011-11-01

The effects of quadrupole moments on the isotropic-nematic (IN) phase transitions are studied using the density-functional theory (DFT) for a Gay-Berne (GB) fluid for a range of length-to-breadth parameters ? in the reduced temperature range ? . The pair-correlation functions of the isotropic phase, which enter into the DFT as input parameters are found by solving the Percus-Yevick integral equation theory. The method used involves an expansion of angle-dependent functions appearing in the integral equations in terms of spherical harmonics and the harmonic coefficients are obtained by an iterative algorithm. All the terms of harmonic coefficients which involve l indices up to less than or equal to 6 are considered. The numerical accuracy of the results depends on the number of spherical harmonic coefficients considered for each orientation-dependent function. As the length-to-breadth ratio of quadrupolar GB molecules is increased, the IN transition is seen to move to lower density (and pressure) at a given temperature. It has been observed that the DFT is good to study the IN transitions in such fluids. The theoretical results have also been compared with the computer simulation results wherever they are available.

Curvature and frontier orbital energies in density functional theory

NASA Astrophysics Data System (ADS)

Kronik, Leeor; Stein, Tamar; Autschbach, Jochen; Govind, Niranjan; Baer, Roi

2013-03-01

Perdew et al. [Phys. Rev. Lett 49, 1691 (1982)] discovered and proved two different properties of exact Kohn-Sham density functional theory (DFT): (i) The exact total energy versus particle number is a series of linear segments between integer electron points; (ii) Across an integer number of electrons, the exchange-correlation potential may ``jump'' by a constant, known as the derivative discontinuity (DD). Here, we show analytically that in both the original and the generalized Kohn-Sham formulation of DFT, the two are in fact two sides of the same coin. Absence of a derivative discontinuity necessitates deviation from piecewise linearity, and the latter can be used to correct for the former, thereby restoring the physical meaning of the orbital energies. Using selected small molecules, we show that this results in a simple correction scheme for any underlying functional, including semi-local and hybrid functionals as well as Hartree-Fock theory, suggesting a practical correction for the infamous gap problem of DFT. Moreover, we show that optimally-tuned range-separated hybrid functionals can inherently minimize both DD and curvature, thus requiring no correction, and show that this can be used as a sound theoretical basis for novel tuning strategies.

Solvent effects on the properties of hyperbranched polythiophenes.

PubMed

Torras, Juan; Zanuy, David; Aradilla, David; Alemán, Carlos

2016-09-21

The structural and electronic properties of all-thiophene dendrimers and dendrons in solution have been evaluated using very different theoretical approaches based on quantum mechanical (QM) and hybrid QM/molecular mechanics (MM) methodologies: (i) calculations on minimum energy conformations using an implicit solvation model in combination with density functional theory (DFT) or time-dependent DFT (TD-DFT) methods; (ii) hybrid QM/MM calculations, in which the solute and solvent molecules are represented at the DFT level as point charges, respectively, on snapshots extracted from classical molecular dynamics (MD) simulations using explicit solvent molecules, and (iii) QM/MM-MD trajectories in which the solute is described at the DFT or TD-DFT level and the explicit solvent molecules are represented using classical force-fields. Calculations have been performed in dichloromethane, tetrahydrofuran and dimethylformamide. A comparison of the results obtained using the different approaches with the available experimental data indicates that the incorporation of effects associated with both the conformational dynamics of the dendrimer and the explicit solvent molecules is strictly necessary to satisfactorily reproduce the properties of the investigated systems. Accordingly, QM/MM-MD simulations are able to capture such effects providing a reliable description of electronic properties-conformational flexibility relationships in all-Th dendrimers.

Molecular structure, spectroscopic (FT-IR, FT Raman, UV, NMR and THz) investigation and hyperpolarizability studies of 3-(2-Chloro-6-fluorophenyl)-1-(2-thienyl) prop-2-en-1-one

NASA Astrophysics Data System (ADS)

Kumar, Rajesh; Kumar, Amit; Deval, Vipin; Gupta, Archana; Tandon, Poonam; Patil, P. S.; Deshmukh, Prathmesh; Chaturvedi, Deepika; Watve, J. G.

2017-02-01

In the present work, a combined experimental and theoretical study on ground state molecular structure, spectroscopic and nonlinear optical properties of the chalcone derivative 3-(2-Chloro-6-fluorophenyl)-1-(2-thienyl) prop-2-en-1-one (2C6F2SC) is reported. Initial geometry generated from single crystal X-ray diffraction parameters was minimized at DFT level employing B3LYP/6-311++G (d,p) without any constraint to the potential energy surface. The molecule has been characterized using various experimental techniques FT-IR, FT-Raman, UV-Vis, 1H NMR, TD-THz and the spectroscopic data have been analyzed theoretically by Density Functional Theory (DFT) method. Harmonic vibrational frequencies were calculated theoretically using the optimized ground state geometry and the spectra were interpreted by means of potential energy distribution. Time Dependent Density Functional Theory (TD-DFT) has been used to calculate energies, absorption wavelengths, oscillator strengths of electronic singlet-singlet transitions. The calculated energy and oscillator strength complement with the experimental findings. The HOMO-LUMO energy gap explains the charge interaction taking place within the molecule. Good correlations between the experimental 1H NMR chemical shifts and calculated GIAO shielding tensors were found. Stability of the molecule, hyperconjugative interactions and charge delocalization has been analyzed by natural bond orbital (NBO) analysis. The first order hyperpolarizability (β) of this molecular system and related properties (μ, <α> and Δα) have been calculated using the finite-field approach.

Benchmarking the Bethe–Salpeter Formalism on a Standard Organic Molecular Set

PubMed Central

2015-01-01

We perform benchmark calculations of the Bethe–Salpeter vertical excitation energies for the set of 28 molecules constituting the well-known Thiel’s set, complemented by a series of small molecules representative of the dye chemistry field. We show that Bethe–Salpeter calculations based on a molecular orbital energy spectrum obtained with non-self-consistent G0W0 calculations starting from semilocal DFT functionals dramatically underestimate the transition energies. Starting from the popular PBE0 hybrid functional significantly improves the results even though this leads to an average −0.59 eV redshift compared to reference calculations for Thiel’s set. It is shown, however, that a simple self-consistent scheme at the GW level, with an update of the quasiparticle energies, not only leads to a much better agreement with reference values, but also significantly reduces the impact of the starting DFT functional. On average, the Bethe–Salpeter scheme based on self-consistent GW calculations comes close to the best time-dependent DFT calculations with the PBE0 functional with a 0.98 correlation coefficient and a 0.18 (0.25) eV mean absolute deviation compared to TD-PBE0 (theoretical best estimates) with a tendency to be red-shifted. We also observe that TD-DFT and the standard adiabatic Bethe–Salpeter implementation may differ significantly for states implying a large multiple excitation character. PMID:26207104

Synthesis, spectroscopic investigation and theoretical studies of 2-((E)-(2-(2-cyanoacetyl)hydrazono)methyl)-4-((E)-phenyldiazenyl)phenyl methyl carbonate

NASA Astrophysics Data System (ADS)

Arokiasamy, A.; Manikandan, G.; Thanikachalam, V.; Gokula Krishnan, K.

2017-04-01

Synthesis and computational optimization studies have been carried out by Hartree-Fock (HF) and Density Functional Theory (DFT-B3LYP) methods with 6-31+G(d, p) basis set for 2-((E)-(2-(2-cyanoacetyl)hydrazono)methyl)-4-((E)-phenyldiazenyl)phenyl methyl carbonate (CHPMC). The stable configuration of CHPMC was confirmed theoretically by potential energy surface scan analysis. The complete vibrational assignments were performed on the basis of total energy distribution (TED) analysis. The vibrational properties studied by IR and Raman spectroscopic data complemented by quantum chemical calculations support the formation of intramolecular hydrogen bond. Furthermore, the UV-Vis spectra are interpreted in terms of TD-DFT quantum chemical calculations. The shapes of the simulated absorption spectra are in good agreement with the experimental data. The comparison between the experimental and theoretical values of FT-IR, FT-Raman vibrational spectra, NMR (1H and 13C) and UV-Vis spectra have also been discussed.

Dynamics of two-phase interfaces and surface tensions: A density-functional theory perspective

NASA Astrophysics Data System (ADS)

Yatsyshin, Petr; Sibley, David N.; Duran-Olivencia, Miguel A.; Kalliadasis, Serafim

2016-11-01

Classical density functional theory (DFT) is a statistical mechanical framework for the description of fluids at the nanoscale, where the inhomogeneity of the fluid structure needs to be carefully accounted for. By expressing the grand free-energy of the fluid as a functional of the one-body density, DFT offers a theoretically consistent and computationally accessible way to obtain two-phase interfaces and respective interfacial tensions in a ternary solid-liquid-gas system. The dynamic version of DFT (DDFT) can be rigorously derived from the Smoluchowsky picture of the dynamics of colloidal particles in a solvent. It is generally agreed that DDFT can capture the diffusion-driven evolution of many soft-matter systems. In this context, we use DDFT to investigate the dynamic behaviour of two-phase interfaces in both equilibrium and dynamic wetting and discuss the possibility of defining a time-dependent surface tension, which still remains in debate. We acknowledge financial support from the European Research Council via Advanced Grant No. 247031 and from the Engineering and Physical Sciences Research Council of the UK via Grants No. EP/L027186 and EP/L020564.

First principle investigation of structural and optical properties of cubic titanium dioxide

NASA Astrophysics Data System (ADS)

Dash, Debashish; Chaudhury, Saurabh; Tripathy, Susanta K.

2018-05-01

This paper presents an analysis of structural and optical properties of cubic titanium dioxide (TiO2) using Orthogonalzed Linear Combinations of Atomic Orbitals (OLCAO) basis set under the framework of Density Functional Theory (DFT). The structural property, specially the lattice constant `a' and the optical properties such as refractive index, extinction coefficient, and reflectivity are investigated and discussed in the energy range of 0-16 eV. Further, the results have compared with previous theoretical as well as with experimental results. It was found that DFT based simulation results are approximation to experimental results.

Structural and electronic properties of GaAs and GaP semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rani, Anita; Kumar, Ranjan

2015-05-15

The Structural and Electronic properties of Zinc Blende phase of GaAs and GaP compounds are studied using self consistent SIESTA-code, pseudopotentials and Density Functional Theory (DFT) in Local Density Approximation (LDA). The Lattice Constant, Equillibrium Volume, Cohesive Energy per pair, Compressibility and Band Gap are calculated. The band gaps calcultated with DFT using LDA is smaller than the experimental values. The P-V data fitted to third order Birch Murnaghan equation of state provide the Bulk Modulus and its pressure derivatives. Our Structural and Electronic properties estimations are in agreement with available experimental and theoretical data.

Caprylate Salts Based on Amines as Volatile Corrosion Inhibitors for Metallic Zinc: Theoretical and Experimental Studies.

PubMed

Valente, Marco A G; Teixeira, Deiver A; Azevedo, David L; Feliciano, Gustavo T; Benedetti, Assis V; Fugivara, Cecílio S

2017-01-01

The interaction of volatile corrosion inhibitors (VCI), caprylate salt derivatives from amines, with zinc metallic surfaces is assessed by density functional theory (DFT) computer simulations, electrochemical impedance (EIS) measurements and humid chamber tests. The results obtained by the different methods were compared, and linear correlations were obtained between theoretical and experimental data. The correlations between experimental and theoretical results showed that the molecular size is the determining factor in the inhibition efficiency. The models used and experimental results indicated that dicyclohexylamine caprylate is the most efficient inhibitor.

Characterization of Meldrum's acid derivative 5-(5-Ethyl-1,3,4-thiadiazol-2-ylamino)methylene-2,2-dimethyl-1,3-dioxane-4,6-dione by Raman and FT-IR spectroscopy and DFT calculations

NASA Astrophysics Data System (ADS)

de Toledo, T. A.; da Silva, L. E.; Teixeira, A. M. R.; Freire, P. T. C.; Pizani, P. S.

2015-07-01

In this study, the structural and vibrational properties of Meldrum's acid derivative 5-(5-Ethyl-1,3,4-thiadiazol-2-ylamino)methylene-2,2-dimethyl-1,3-dioxane-4,6-dione, C11H13N3O4S were studied combining experimental techniques such as Raman and FT-IR spectroscopy and density functional theory (DFT) calculations. The Raman and FT-IR spectra were recorded at room conditions in the regions from 80 to 3400 cm-1 and 400 to 4000 cm-1, respectively. Vibrational wavenumbers were predicted using DFT calculations with the hybrid functional B3LYP and basis set 6-31G(d,p). A comparison between experimental and theoretical data is provided for the Raman and FT-IR spectra. The descriptions of the normal modes were carried by means of potential energy distribution (PED).

Theoretical design of near - infrared organic compounds

NASA Astrophysics Data System (ADS)

Brymora, Katarzyna; Ducasse, Laurent; Dautel, Olivier; Lartigau-Dagron, Christine; Castet, FréDéRic

The world follows the path of digital development faster than ever before. In consequence, the Human Machine Interfaces (HMI) market is growing as well and it requires some innovations. The goal of our work is to achieve an organic Infra-Red (IR) photodetectors hitting the performance requirements for HMI applications. The quantum chemical calculations are used to guide the synthesis and technology development. In this work, in the framework of density functional theory (DFT) and time-dependent density functional theory (TD-DFT), we consider a large variety of materials exploring small donor-acceptor-donor molecules and copolymers alternating donor and acceptor monomers. We provide a structure-property relationship in view of designing new Near-Infrared (NIR) absorbing organic molecules and polymers.

Probing the 5 f electrons in Am-I by hybrid density functional theory

NASA Astrophysics Data System (ADS)

Atta-Fynn, Raymond; Ray, Asok K.

2009-11-01

The ground states of the actinides and their compounds continue to be matters of considerable controversies. Experimentally, Americium-I (Am-I) is a non-magnetic dhcp metal whereas theoretically an anti-ferromagnetic ground state is predicted. We show that hybrid density functional theory, which admixes a fraction, λ, of exact Hartree-Fock (HF) exchange with approximate DFT exchange, can correctly reproduce the ground state properties of Am. In particular, for λ=0.40, we obtain a non-magnetic ground state with equilibrium atomic volume, bulk modulus, 5 f electron population, and the density of electronic states all in good agreement with experimental data. We argue that the exact HF exchange corrects the overestimation of the approximate DFT exchange interaction.

Density functional theory: Foundations reviewed

NASA Astrophysics Data System (ADS)

Kryachko, Eugene S.; Ludeña, Eduardo V.

2014-11-01

Guided by the above motto (quotation), we review a broad range of issues lying at the foundations of Density Functional Theory, DFT, a theory which is currently omnipresent in our everyday computational study of atoms and molecules, solids and nano-materials, and which lies at the heart of modern many-body computational technologies. The key goal is to demonstrate that there are definitely the ways to improve DFT. We start by considering DFT in the larger context provided by reduced density matrix theory (RDMT) and natural orbital functional theory (NOFT), and examine the implications that N-representability conditions on the second-order reduced density matrix (2-RDM) have not only on RDMT and NOFT but, also, by extension, on the functionals of DFT. This examination is timely in view of the fact that necessary and sufficient N-representability conditions on the 2-RDM have recently been attained. In the second place, we review some problems appearing in the original formulation of the first Hohenberg-Kohn theorem which is still a subject of some controversy. In this vein we recall Lieb's comment on this proof and the extension to this proof given by Pino et al. (2009), and in this context examine the conditions that must be met in order that the one-to-one correspondence between ground-state densities and external potentials remains valid for finite subspaces (namely, the subspaces where all Kohn-Sham solutions are obtained in practical applications). We also consider the issue of whether the Kohn-Sham equations can be derived from basic principles or whether they are postulated. We examine this problem in relation to ab initio DFT. The possibility of postulating arbitrary Kohn-Sham-type equations, where the effective potential is by definition some arbitrary mixture of local and non-local terms, is discussed. We also deal with the issue of whether there exists a universal functional, or whether one should advocate instead the construction of problem-geared functionals. These problems are discussed by making reference to ab initio DFT as well as to the local-scaling-transformation version of DFT, LS-DFT. In addition, we examine the question of the accuracy of approximate exchange-correlation functionals in the light of their non-observance of the variational principle. Why do approximate functionals yield reasonable (and accurate) descriptions of many molecular and condensed matter properties? Are the conditions imposed on exchange and correlation functionals sufficiently adequate to produce accurate semi-empirical functionals? In this respect, we consider the question of whether the results reflect a true approach to chemical accuracy or are just the outcome of a virtuoso-like performance which cannot be systematically improved. We discuss the issue of the accuracy of the contemporary DFT results by contrasting them to those obtained by the alternative RDMT and NOFT. We discuss the possibility of improving DFT functionals by applying in a systematic way the N-representability conditions on the 2-RDM. In this respect, we emphasize the possibility of constructing 2-matrices in the context of the local scaling transformation version of DFT to which the N-representability condition of RDM theory may be applied. We end up our revision of HKS-DFT by considering some of the problems related to spin symmetry and discuss some current issues dealing with a proper treatment of open-shell systems. We are particularly concerned, as in the rest of this paper, mostly with foundational issues arising in the construction of functionals. We dedicate the whole Section 4 to the local-scaling transformation version of density functional theory, LS-DFT. The reason is that in this theory some of the fundamental problems that appear in HKS-DFT, have been solved. For example, in LS-DFT the functionals are, in principle, designed to fulfill v- and N-representability conditions from the outset. This is possible because LS-DFT is based on density transformation (local-scaling of coordinates proceeds through density transformation) and so, because these functionals are constructed from prototype N-particle wavefunctions, the ensuing density functionals already have built-in N-representability conditions. This theory is presented in great detail with the purpose of illustrating an alternative way to HKS-DFT which could be used to improve the construction of HKS-DFT functionals. Let us clearly indicate, however, that although appealing from a theoretical point of view, the actual application of LS-DFT to large systems has not taken place mostly because of technical difficulties. Thus, our aim in introducing this theory is to foster a better understanding of its foundations with the hope that it may promote a cross-hybridization with the already existing approaches. Also, to complete our previous discussion on symmetry, in particular, spin-symmetry, we discuss this issue from the perspective of LS-DFT. Finally, in Section 6, we discuss dispersion molecular forces emphasizing their relevance to DFT approaches.

Structural characterization, vibrational study, NLO and DFT calculations of a novel organic sulfate monohydrate templated with (S)-(-)-2,6-diammonium-4,5,6,7-tetrahydrobenzothiazole

NASA Astrophysics Data System (ADS)

Barhoumi, Abir; Mhiri, Tahar; Dammak, Thameur; Suñol, Joan Josep; Belhouchet, Mohamed

2017-01-01

A single crystal of (S)-(-)-2,6-diammonium-4,5,6,7-tetrahydrobenzothiazole sulfate monohydrate has been synthesized and grown at room temperature by slow evaporation of aqueous solution. The studied compound crystallizes in the space group P212121 of the orthorhombic system with cell parameters a = 7.0014(12), b = 8.7631(15), c = 19.773(3) Å. We report the molecular structure and the theoretical and experimental vibrational spectra of the synthesized compound. The atomic arrangement, which is an alternation of organic inorganic layers linked together through hydrogen bonds, gives rise to three types of rings formed by the interconnection of organic-inorganic entities. The experimental FT-IR and the Raman spectra the synthesized compound were recorded and analyzed. The peaks assignment has been made unambiguously from the literature. To confirm the assignment, the experimental spectra were compared with theoretical spectra obtained with the Gaussian 98 program by the Density Functional Theory (DFT) method using B3LYP function with the LanL2DZ basis set. Moreover, to study the nonlinear optical (NLO) property of this compound, the hyperpolarizability βtot, the electric dipole μtot and the polarizability αtot were calculated using the DFT. Based on our calculation the synthesized compound has a non-zero hyperpolarizability suggesting that it may be used in some NLO applications.

DFT-Assisted Polymorph Identification from Lattice Raman Fingerprinting

PubMed Central

2017-01-01

A combined experimental and theoretical approach, consisting of lattice phonon Raman spectroscopy and density functional theory (DFT) calculations, is proposed as a tool for lattice dynamics characterization and polymorph phase identification. To illustrate the reliability of the method, the lattice phonon Raman spectra of two polymorphs of the molecule 2,7-dioctyloxy[1]benzothieno[3,2-b]benzothiophene are investigated. We show that DFT calculations of the lattice vibrations based on the known crystal structures, including many-body dispersion van der Waals (MBD-vdW) corrections, predict experimental data within an accuracy of ≪5 cm–1 (≪0.6 meV). Due to the high accuracy of the simulations, they can be used to unambiguously identify different polymorphs and to characterize the nature of the lattice vibrations and their relationship to the structural properties. More generally, this work implies that DFT-MBD-vdW is a promising method to describe also other physical properties that depend on lattice dynamics like charge transport. PMID:28731723

The biomolecule, 2-[(2-methoxyl)sulfanyl]-4-(2-methylpropyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile: FT-IR, Laser-Raman spectra and DFT.

PubMed

Sert, Yusuf; El-Emam, Ali A; Al-Deeb, Omar A; Al-Turkistani, Abdulghafoor A; Ucun, Fatih; Cırak, Cağrı

2014-05-21

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized potential chemotherapeutic agent namely, 2-[(2-methoxyl)sulfanyl]-4-(2-methylpropyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile have been investigated. The experimental FT-IR (4000-400cm(-1)) and Laser-Raman spectra (4000-100cm(-1)) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with the results in the literature. In addition, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy and the other related molecular energy values of the compound have been investigated using the same theoretical calculations. Copyright © 2014 Elsevier B.V. All rights reserved.

Stereoselective green synthesis and molecular structures of highly functionalized spirooxindole-pyrrolidine hybrids - A combined experimental and theoretical investigation

NASA Astrophysics Data System (ADS)

Kumar, Raju Suresh; Almansour, Abdulrahman I.; Arumugam, Natarajan; Soliman, Saied M.; Kumar, Raju Ranjith; Altaf, Mohammad; Ghabbour, Hazem A.; Krishnamoorthy, Bellie Sundaram

2018-01-01

Highly functionalized spirooxindole-pyrrolidine hybrids have been synthesized stereoselectively through a [3 + 2] cycloaddition strategy in an ionic liquid, 1-butyl-3-methylimidazolium bromide ([bmim]Br). The structure of these spiro heterocyclic hybrids was elucidated using one and two dimensional NMR spectroscopy, single crystal X-ray crystallographic studies and Density Functional Theory (DFT) calculations. The calculated geometric parameters are in good agreement with the experimental data obtained from the X-ray structures. The Natural Bond Orbital (NBO) calculations on these molecules confirm the electron rich carbonyl oxygen and electron deficient NH groups. The 1H and 13C NMR chemical shifts calculated using GIAO method are in good agreement with the experimental data. The DFT computed polarizability values also suggest the possible NLO activity of these molecules.

Synthesis, spectroscopic characterization, theoretical study and anti-hepatic cancer activity study of 4-(1E,3Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-1,3,6-trien-1-yl)-2-methoxyphenyl 4-nitrobenzoate, a novel curcumin congener

NASA Astrophysics Data System (ADS)

Srivastava, Sangeeta; Gupta, Preeti; Singh, Ranvijay Pratap; Jafri, Asif; Arshad, M.; Banerjee, Monisha

2017-08-01

In the present work 4-(1E,3Z,6E)-3-hydroxy-7-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-1,3,6-trien-1-yl)-2-methoxyphenyl 4-nitrobenzoate (2), a novel curcumin ester was synthesized. The molecular structure and spectroscopic analysis were performed using experimental techniques like FT-IR, 1H,13C NMR, mass and UV-visible as well as theoretical calculations. The theoretical calculations were done by DFT level of theory using B3LYP/6-31G (d,p) basis set. The vibrational wavenumbers were calculated using DFT method and assigned with the help of potential energy distribution (PED). The electronic properties such as frontier orbitals and band gap energies have been calculated using time dependent density functional theory (TD-DFT). The strength and nature of weak intramolecular interactions have been studied by AIM approach. Global and local reactivity descriptors have been computed to predict reactivity and reactive sites in the molecule. First hyperpolarizability values have been calculated to describe the nonlinear optical (NLO) property of the synthesized compounds. Molecular electrostatic potential (MEP) analysis has also been carried out. The anti-hepatic cancer activity of compound 2 was also carried out.

Unscrambling micro-solvation of -COOH and -NH groups in neat dimethyl sulfoxide: insights from 1H-NMR spectroscopy and computational studies.

PubMed

Takis, Panteleimon G; Papavasileiou, Konstantinos D; Peristeras, Loukas D; Boulougouris, Georgios C; Melissas, Vasilios S; Troganis, Anastassios N

2017-05-31

Dimethyl sulfoxide (DMSO) has a significant, multi-faceted role in medicine, pharmacy, and biology as well as in biophysical chemistry and catalysis. Its physical properties and impact on biomolecular structures still attract major scientific interest, especially the interactions of DMSO with biomolecular functional groups. In the present study, we shed light on the "isolated" carboxylic (-COOH) and amide (-NH) interactions in neat DMSO via 1 H NMR studies along with extensive theoretical approaches, i.e. molecular dynamics (MD) simulations, density functional theory (DFT), and ab initio calculations, applied on model compounds (i.e. acetic and benzoic acid, ethyl acetamidocyanoacetate). Both experimental and theoretical results show excellent agreement, thereby permitting the calculation of the association constants between the studied compounds and DMSO molecules. Our coupled MD simulations, DFT and ab initio calculations, and NMR spectroscopy results indicated that complex formation is entropically driven and DMSO molecules undergo multiple strong interactions with the studied molecules, particularly with the -COOH groups. The combined experimental and theoretical techniques unraveled the interactions of DMSO with the most abundant functional groups of peptides (i.e. peptide bonds, side chain and terminal carboxyl groups) in high detail, providing significant insights on the underlying thermodynamics driving these interactions. Moreover, the developed methodology for the analysis of the simulation results could serve as a template for future thermodynamic and kinetic studies of similar systems.

DFT simulation, quantum chemical electronic structure, spectroscopic and structure-activity investigations of 4-acetylpyridine

NASA Astrophysics Data System (ADS)

Atilgan, A.; Yurdakul, Ş.; Erdogdu, Y.; Güllüoğlu, M. T.

2018-06-01

The spectroscopic (UV-Vis and infrared), structural and some electronic property observations of the 4-acetylpyridine (4-AP) were reported, which are investigated by using some spectral methods and DFT calculations. FT-IR spectra were obtained for 4-AP at room temperature in the region 4000 cm-1- 400 cm-1. In the DFT calculations, the B3LYP functional with 6-311G++G(d,p) basis set was applied to carry out the quantum mechanical calculations. The Fourier Transform Infrared (FT-IR) and FT-Raman spectra were interpreted by using of normal coordinate analysis based on scaled quantum mechanical force field. The present work expands our understanding of the both the vibrational and structural properties as well as some electronic properties of the 4-AP by means of the theoretical and experimental methods.

The effect of different π-bridge configuration on bi-anchored triphenylamine and phenyl modified triphenylamine based dyes for dye sensitized solar cell (DSSC) application: A theoretical approach.

PubMed

Pounraj, P; Mohankumar, V; Pandian, M Senthil; Ramasamy, P

2018-01-01

Twenty eight bi-anchored triphenylamine (TH-1 to TH-14) and phenyl modified triphenylamine (PH-TH-1 to PH-TH-14) based metal free organic dyes are designed for DSSC application. The electronic effect of different π-bridge configurations in donor-π-bridge-acceptor (D-π-A) 2 structure was theoretically simulated and verified using density functional theory (DFT) and time dependent density functional theory (TD-DFT). The triphenylamine and phenyl modified triphenylamine groups are used as donor and cyanoacrylic acid group is used as acceptor. Thiophene and cyanovinyl groups are used as π-bridge. The ground state molecular structure was optimized by density functional theory and the electronic absorption spectra were calculated by time dependent density functional theory. The light harvesting efficiency (LHE), dye regeneration energy (ΔG reg ) and electron injection energy (ΔG inject ) are determined by computational examination. It is observed that, when the number of π-bridge increases, the band gap of the dye decreases. Also the absorption maximum and molar extinction coefficient of the dyes are increased. Theoretical result shows that the thiophene-cyanovinyl and thiophene-thiophene-cyanovinyl-cyanovinyl configurations give broader and red shifted absorption spectrum compared to other configurations. Also the results of phenyl modified triphenylamine (PH-TH) dyes clearly show better absorption and dye regeneration energy compared to TH dyes. Copyright © 2017 Elsevier Inc. All rights reserved.

Investigation of structure, vibrational and NMR spectra of oxycodone and naltrexone: A combined experimental and theoretical study

NASA Astrophysics Data System (ADS)

Tavakol, Hossein; Esfandyari, Maryam; Taheri, Salman; Heydari, Akbar

2011-08-01

In this work, two important opioid antagonists, naltrexone and oxycodone, were prepared from thebaine and were characterized by IR, 1H NMR and 13C NMR spectroscopy. Moreover, computational NMR and IR parameters were obtained using density functional theory (DFT) at B3LYP/6-311++G** level of theory. Complete NMR and vibrational assignment were carried out using the observed and calculated spectra. The IR frequencies and NMR chemical shifts, determined experimentally, were compared with those obtained theoretically from DFT calculations, showed good agreements. The RMS errors observed between experimental and calculated data for the IR absorptions are 85 and 105 cm -1, for the 1H NMR peaks are 0.87 and 0.17 ppm and for those of 13C NMR are 5.6 and 5.3 ppm, respectively for naltrexone and oxycodone.

Structural investigation, spectroscopic and energy level studies of Schiff base: 2-[(3‧-N-salicylidenephenyl)benzimidazole] using experimental and DFT methods

NASA Astrophysics Data System (ADS)

Suman, G. R.; Bubbly, S. G.; Gudennavar, S. B.; Muthu, S.; Roopashree, B.; Gayatri, V.; Nanje Gowda, N. M.

2017-07-01

The Schiff base 2-[(3‧-N-salicylidenephenyl)benzimidazole] (Spbzl) was characterized by FT-Raman, 1H NMR, 13C NMR and single crystal X-ray diffraction technique. Crystallographic studies reveal the presence of two water molecules in the asymmetry unit which aid the intermolecular hydrogen bonding with imidazole ring, and the trans-conformation of the azomethine bond. Theoretical computations conducted using density functional theory (DFT) analysis support the experimental facts. Energy levels estimated by DFT studies are in good agreement with the values obtained from cyclic voltammetry technique. Frontier molecular orbital analysis shows that charge transfer has taken place from donor to acceptor moiety, which is also supported by the high hyperpolarizability values in both gaseous and solution phases, indicating high charge transfer capability of the molecule. A comparative theoretical study of Spbzl with derivative 4-((3-(1H-benzimidazol-2-yl)phenylimino)methyl)-3-hydroxybenzoic acid (Pbzlb) having an added anchor group COOH substituted at para position in the acceptor ring has been made. The result shows the feasibility of charge transfer to the semiconductor surface in dye sensitized solar cell (DSSC) applications for Pbzlb.

Mixed-ligand cobalt(II) complexes of bioinorganic and medicinal relevance, involving dehydroacetic acid and β-diketones: Their synthesis, hyphenated experimental-DFT, thermal and bactericidal facets

NASA Astrophysics Data System (ADS)

Maurya, R. C.; Malik, B. A.; Mir, J. M.; Vishwakarma, P. K.; Rajak, D. K.; Jain, N.

2015-11-01

The present report pertains to synthesis and combined experimental-DFT studies of a series of four novel mixed-ligand complexes of cobalt(II) of the general composition [Co(dha)(L)(H2O)2], where dhaH = dehydroacetic acid, LH = β-ketoenolates viz., o-acetoacetotoluidide (o-aatdH), o-acetoacetanisidide (o-aansH), acetylacetone (acacH) or 1-benzoylacetone (1-bac). The resulting complexes were formulated based on elemental analysis, molar conductance, magnetic measurements, mass spectrometric, IR, electronic, electron spin resonance and cyclic voltammetric studies. The TGA based thermal behavior of one representative complex was evaluated. Molecular geometry optimizations and vibrational frequency calculations have been performed with Gaussian 09 software package by using density functional theory (DFT) methods with B3LYP/LANL2MB combination for dhaH and one of its complexes, [Co(dha)(1-bac)(H2O)2]. Theoretical data has been found in an excellent agreement with the experimental results. Based on experimental and theoretical data, suitable trans-octahedral structure has been proposed for the present class of complexes. Moreover, the complexes also showed a satisfactory antibacterial activity.

Periodic subsystem density-functional theory

NASA Astrophysics Data System (ADS)

Genova, Alessandro; Ceresoli, Davide; Pavanello, Michele

2014-11-01

By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem Density Functional Theory (DFT) has recently emerged as a powerful tool for reducing the computational scaling of Kohn-Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extending FDE to treat subsystems of molecular and periodic character. This goal is achieved by a dual approach. On one side, the development of a theoretical framework for periodic subsystem DFT. On the other, the realization of the method into a parallel computer code. We find that periodic FDE is capable of reproducing total electron densities and (to a lesser extent) also interaction energies of molecular systems weakly interacting with metallic surfaces. In the pilot calculations considered, we find that FDE fails in those cases where there is appreciable density overlap between the subsystems. Conversely, we find FDE to be in semiquantitative agreement with Kohn-Sham DFT when the inter-subsystem density overlap is low. We also conclude that to make FDE a suitable method for describing molecular adsorption at surfaces, kinetic energy density functionals that go beyond the GGA level must be employed.

Periodic subsystem density-functional theory.

PubMed

Genova, Alessandro; Ceresoli, Davide; Pavanello, Michele

2014-11-07

By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem Density Functional Theory (DFT) has recently emerged as a powerful tool for reducing the computational scaling of Kohn-Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extending FDE to treat subsystems of molecular and periodic character. This goal is achieved by a dual approach. On one side, the development of a theoretical framework for periodic subsystem DFT. On the other, the realization of the method into a parallel computer code. We find that periodic FDE is capable of reproducing total electron densities and (to a lesser extent) also interaction energies of molecular systems weakly interacting with metallic surfaces. In the pilot calculations considered, we find that FDE fails in those cases where there is appreciable density overlap between the subsystems. Conversely, we find FDE to be in semiquantitative agreement with Kohn-Sham DFT when the inter-subsystem density overlap is low. We also conclude that to make FDE a suitable method for describing molecular adsorption at surfaces, kinetic energy density functionals that go beyond the GGA level must be employed.

DFT and PCM-TD-DFT investigation of the electronic structures and spectra of 5-(3-phenyl-2-propenylidene)-2-thioxo-4-thiazolidinone derivatives

NASA Astrophysics Data System (ADS)

El-Taher, Sabry; Metwaly, Mohamed

2017-04-01

UV-Visible absorption spectra of 5-(3-phenyl-2-propenylidene)-2-thioxo-4-thiazolidinones (5pR-PPTT, R = H, CH3, CH3O, and N(CH3)2) were measured in different solvents and investigated using the theoretical PCM-TD-DFT scheme. A benchmark evaluation against experimental results on the accuracy of different DFT functionals has been performed. The best agreement with X-ray data is achieved by using the long-range corrected LC-wPBE functional, while the PBE0 functional provided the most accurate λmax for the studied compounds. The thionic forms of the ZE isomers of the studied compounds are found to be the most stable tautomers. The assignation debate of the second absorption band of rhodanine [2-thioxo-4-thiazolidinone (Rd)] has been solved by confirming on its π-π∗ nature. It was found that the expansion of the π-conjugation system at position 5 of Rd ring leads to significant bathochromic shift. The CT lengths (Δr) and dipole moment change (ΔμCT) indices showed that the charge transfer character of the electronic transitions is directly proportional to the electron-releasing strength of substituted phenyl ring. It was concluded that the red shifting of the maximum absorption is mainly regulated by the solvent polarizability and much less by solvent polarity.

Periodic subsystem density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Genova, Alessandro; Pavanello, Michele, E-mail: m.pavanello@rutgers.edu; Ceresoli, Davide

2014-11-07

By partitioning the electron density into subsystem contributions, the Frozen Density Embedding (FDE) formulation of subsystem Density Functional Theory (DFT) has recently emerged as a powerful tool for reducing the computational scaling of Kohn–Sham DFT. To date, however, FDE has been employed to molecular systems only. Periodic systems, such as metals, semiconductors, and other crystalline solids have been outside the applicability of FDE, mostly because of the lack of a periodic FDE implementation. To fill this gap, in this work we aim at extending FDE to treat subsystems of molecular and periodic character. This goal is achieved by a dualmore » approach. On one side, the development of a theoretical framework for periodic subsystem DFT. On the other, the realization of the method into a parallel computer code. We find that periodic FDE is capable of reproducing total electron densities and (to a lesser extent) also interaction energies of molecular systems weakly interacting with metallic surfaces. In the pilot calculations considered, we find that FDE fails in those cases where there is appreciable density overlap between the subsystems. Conversely, we find FDE to be in semiquantitative agreement with Kohn–Sham DFT when the inter-subsystem density overlap is low. We also conclude that to make FDE a suitable method for describing molecular adsorption at surfaces, kinetic energy density functionals that go beyond the GGA level must be employed.« less

Theoretical study of triaxial shapes of neutron-rich Mo and Ru nuclei

DOE PAGES

Zhang, C. L.; Bhat, G. H.; Nazarewicz, W.; ...

2015-09-10

Here, whether atomic nuclei can possess triaxial shapes at their ground states is still a subject of ongoing debate. According to theory, good prospects for low-spin triaxiality are in the neutron-rich Mo-Ru region. Recently, transition quadrupole moments in rotational bands of even-mass neutron-rich isotopes of molybdenum and ruthenium nuclei have been measured. The new data have provided a challenge for theoretical descriptions invoking stable triaxial deformations. The purpose of this study is to understand experimental data on rotational bands in the neutron-rich Mo-Ru region, we carried out theoretical analysis of moments of inertia, shapes, and transition quadrupole moments of neutron-richmore » even-even nuclei around 110Ru using self-consistent mean-field and shell model techniques. Methods: To describe yrast structures in Mo and Ru isotopes, we use nuclear density functional theory (DFT) with the optimized energy density functional UNEDF0. We also apply triaxial projected shell model (TPSM) to describe yrast and positive-parity, near-yrast band structures. As a result, our self-consistent DFT calculations predict triaxial ground-state deformations in 106,108Mo and 108,110,112Ru and reproduce the observed low-frequency behavior of moments of inertia. As the rotational frequency increases, a negative-gamma structure, associated with the aligned ν(h 11/2) 2 pair, becomes energetically favored. The computed transition quadrupole moments vary with angular momentum, which reflects deformation changes with rotation; those variations are consistent with experiment. The TPSM calculations explain the observed band structures assuming stable triaxial shapes. Lastly, the structure of neutron-rich even-even nuclei around Ru-110 is consistent with triaxial shape deformations. Our DFT and TPSM frameworks provide a consistent and complementary description of experimental data.« less

Structural characterization, solvent effects on nuclear magnetic shielding tensors, experimental and theoretical DFT studies on the vibrational and NMR spectra of 3-(acrylamido)phenylboronic acid

NASA Astrophysics Data System (ADS)

Alver, Özgür; Kaya, Mehmet Fatih; Dikmen, Gökhan

2015-12-01

Structural elucidation of 3-(acrylamido)phenylboronic acid (C9H10BNO3) was carried out with 1H, 13C and HETCOR NMR techniques. Solvent effects on nuclear magnetic shielding tensors were examined with deuterated dimethyl sulfoxide, acetone, methanol and water solvents. The correct order of appearance of carbon and hydrogen atoms on NMR scale from highest magnetic field region to the lowest one were investigated using different types of theoretical levels and the details of the levels were presented in this study. Stable structural conformers and vibrational band analysis of the title molecule (C9H10BNO3) were studied both experimental and theoretical viewpoints using FT-IR, Raman spectroscopic methods and density functional theory (DFT). FT-IR and Raman spectra were obtained in the region of 4000-400 cm-1, and 3700-10 cm-1, respectively. Becke-3-Lee-Yang-Parr (B3LYP) hybrid density functional theory method with 6-31++G(d, p) basis set was included in the search for optimized structures and vibrational wavenumbers. Experimental and theoretical results show that after application of a suitable scaling factor density functional B3LYP method resulted in acceptable results for predicting vibrational wavenumbers except OH and NH stretching modes which is most likely arising from increasing unharmonicity in the high wave number region and possible intra and inter molecular interaction at OH edges those of which are not fully taken into consideration in theoretical processes. To make a more quantitative vibrational assignments, potential energy distribution (PED) values were calculated using VEDA 4 (Vibrational Energy Distribution Analysis) program.

Theoretical study of NMR, infrared and Raman spectra on triple-decker phthalocyanines

NASA Astrophysics Data System (ADS)

Suzuki, Atsushi; Oku, Takeo

2016-02-01

Electronic structures and magnetic properties of multi-decker phthalocyanines were studied by theoretical calculation. Electronic structures, excited processes at multi-states, isotropic chemical shifts of 13C, 14N and 1H-nuclear magnetic resonance (NMR), principle V-tensor in electronic field gradient (EFG) tensor and asymmetry parameters (η), vibration mode in infrared (IR) and Raman spectra of triple-decker phthalocyanines were calculated by density functional theory (DFT) and time-dependent DFT using B3LYP as basis function. Electron density distribution was delocalized on the phthalocyanine rings with electron static potential. Considerable separation of chemical shifts in 13C, 14N and 1H-NMR was originated from nuclear spin interaction between nitrogen and carbon atoms, nuclear quadrupole interaction based on EFG and η of central metal under crystal field. Calculated optical absorption at multi-excited process was derived from overlapping π-orbital on the phthalocyanine rings. The vibration modes in IR and Raman spectra were based on in-plane deformation and stretching vibrations of metal-ligand coordination bond on the deformed structure.

3-Iodobenzaldehyde: XRD, FT-IR, Raman and DFT studies.

PubMed

Kumar, Chandraju Sadolalu Chidan; Parlak, Cemal; Tursun, Mahir; Fun, Hoong-Kun; Rhyman, Lydia; Ramasami, Ponnadurai; Alswaidan, Ibrahim A; Keşan, Gürkan; Chandraju, Siddegowda; Quah, Ching Kheng

2015-06-15

The structure of 3-iodobenzaldehyde (3IB) was characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of 3IB were examined using density functional theory (DFT) method, with the Becke-3-Lee-Yang-Parr (B3LYP) functional and the 6-311+G(3df,p) basis set for all atoms except for iodine. The LANL2DZ effective core basis set was used for iodine. Potential energy distribution (PED) analysis of normal modes was performed to identify characteristic frequencies. 3IB crystallizes in monoclinic space group P21/c with the O-trans form. There is a good agreement between the theoretically predicted structural parameters, and vibrational frequencies and those obtained experimentally. In order to understand halogen effect, 3-halogenobenzaldehyde [XC6H4CHO; X=F, Cl and Br] was also studied theoretically. The free energy difference between the isomers is small but the rotational barrier is about 8kcal/mol. An atypical behavior of fluorine affecting conformational preference is observed. Copyright © 2015 Elsevier B.V. All rights reserved.

Adsorption of rare gases on the C20 nanocage: a theoretical investigation

NASA Astrophysics Data System (ADS)

Rahimi, Rezvan; Kamalinahad, Saeedeh; Solimannejad, Mohammad

2018-03-01

The adsorption of rare gases (Rg) on the external surface of pristine and Sc-doped C20 (ScC19) nanocage is investigated using density functional theory (DFT). Also, time-dependent density functional theory (TD-DFT) and natural bond orbital (NBO) calculations are performed at the CAM-B3LYP/6-31G (d) level. The NBO analyses indicate that the adsorption of Rg molecules with studied nanocage significantly alters its electronic nature. Theoretical results have shown that Rg is weakly adsorbed on the pristine C20, so this nanocage cannot be a proper sensor for detecting and sensing rare gases. In order to improve properties of the nanocage as a promising sensor, Sc-doping process was investigated. The more negative adsorption energies (Eads) of Rg/ScC19 means that adsorption of Rg on the surface of ScC19 is energetically more favored than C20 and other nano-structures as reported in previous studies. It is expected that significant changes in the electronic properties caused by Rg may be used for designing new sensors for detection of rare gases.

Corrosion Study of Mild Steel in Aqueous Sulfuric Acid Solution Using 4-Methyl-4H-1,2,4-Triazole-3-Thiol and 2-Mercaptonicotinic Acid—An Experimental and Theoretical Study

PubMed Central

Mehmeti, Valbonë V.; Berisha, Avni R.

2017-01-01

The corrosion behavior of mild steel in 0.1 M aqueous sulfuric acid medium has been studied using weight loss, potentiodynamic polarization measurements, quantum chemical calculations, and molecular dynamic simulations in the presence and absence of 4-methyl-4H-1,2,4-triazole-3-thiol and 2-mercaptonicotinic acid. Potentiodynamic measurements indicate that these compounds mostly act as mixed inhibitors due to their adsorption on the mild steel surface. The goal of the study was to use theoretical calculations to better understand the inhibition. Monte Carlo simulation was used to calculate the adsorption behavior of the studied molecules onto Fe (1 1 1) and Fe2O3 (1 1 1) surface. The molecules were also studied with the density functional theory (DFT), using the B3LYP functional in order to determine the relationship between the molecular structure and the corrosion inhibition behavior. More accurate adsorption energies between the studied molecules and iron or iron oxide were calculated by using DFT with periodic boundary conditions. The calculated theoretical parameters gave important assistance into the understanding the corrosion inhibition mechanism expressed by the molecules and are in full agreement with the experimental results. PMID:28971092

Solid-state cocrystal formation between acyclovir and fumaric acid: Terahertz and Raman vibrational spectroscopic studies.

PubMed

Cai, Qiang; Xue, Jiadan; Wang, Qiqi; Du, Yong

2017-11-05

The vibrational spectra of solid-state acyclovir, fumaric acid and their cocrystal have been investigated by using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. In experimental THz spectra, the cocrystal has absorption peaks in 0.65, 0.94 and 1.10THz respectively, while the raw materials are absolutely different in this region. Raman spectra also show similar results about differences between the cocrystal and raw materials. Density functional theory (DFT) was performed to simulate vibrational modes of different theoretical forms between acyclovir and fumaric acid. The calculation of theoretical THz spectra shows that O8C7N1H27 and the carboxyl group COOH establish a dimer theoretical cocrystal form by the hydrogen bonding effect, which makes contributions to the formation of absorption peaks in 0.70, 1.01 and 1.34THz, and agrees well with experimental observations. The theoretical Raman result also indicates that this dimer form matches with experimental results. The characteristic bands of the cocrystal between acyclovir and fumaric acid are also assigned based on the simulation results from the DFT calculation. Copyright © 2017 Elsevier B.V. All rights reserved.

Solid-state cocrystal formation between acyclovir and fumaric acid: Terahertz and Raman vibrational spectroscopic studies

NASA Astrophysics Data System (ADS)

Cai, Qiang; Xue, Jiadan; Wang, Qiqi; Du, Yong

2017-11-01

The vibrational spectra of solid-state acyclovir, fumaric acid and their cocrystal have been investigated by using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. In experimental THz spectra, the cocrystal has absorption peaks in 0.65, 0.94 and 1.10 THz respectively, while the raw materials are absolutely different in this region. Raman spectra also show similar results about differences between the cocrystal and raw materials. Density functional theory (DFT) was performed to simulate vibrational modes of different theoretical forms between acyclovir and fumaric acid. The calculation of theoretical THz spectra shows that O8dbnd C7sbnd N1sbnd H27 and the carboxyl group sbnd COOH establish a dimer theoretical cocrystal form by the hydrogen bonding effect, which makes contributions to the formation of absorption peaks in 0.70, 1.01 and 1.34 THz, and agrees well with experimental observations. The theoretical Raman result also indicates that this dimer form matches with experimental results. The characteristic bands of the cocrystal between acyclovir and fumaric acid are also assigned based on the simulation results from the DFT calculation.

Molecular structure, nonlinear optical studies and spectroscopic analysis of chalcone derivative (2E)-3-[4-(methylsulfanyl) phenyl]-1-(3-bromophenyl) prop-2-en-1-one by DFT calculations

NASA Astrophysics Data System (ADS)

Kumar, Amit; Kumar, Rajesh; Gupta, Archana; Tandon, Poonam; D'silva, E. Deepak

2017-12-01

A collective experimental and theoretical study was conducted on the molecular structure and vibrational spectra of nonlinear optical chalcone derivative (2E)-3-[4-(methylsulfanyl) phenyl]-1-(3-bromophenyl) prop-2-en-1-one (3Br4MSP). The FT-IR and FT-Raman spectra of the molecule in the solid phase have been recorded. Density functional theory (DFT) calculations at B3LYP level with 6-311++G (d,p) basis set have been carried out to derive useful information about the molecular structure and to assign the relevant electronic and vibrational features. These calculations reveal that the optimized geometry closely resembles the experimental XRD data. The vibrational spectra were analyzed on the basis of the potential energy distribution (PED) of each vibrational mode, which allowed us to obtain a quantitative as well as qualitative interpretation of FT-IR and FT-Raman spectra. The UV-vis spectrum was recorded in methanol solution. The excited state properties have been determined by TD-DFT method and the effect of solvent was analyzed by PCM model. The most prominent transition corresponds to π→π∗. The reactivity parameters as chemical potential, global hardness, and electrophilicity index have also been calculated. To provide an explicit assignment and analysis of 13C and 1H NMR spectra, theoretical calculations on chemical shift of the title compound were done through GIAO method at B3LYP/6-311++G (d,p) level. The Mulliken's population analysis shows one of the simplest pictures of charge distribution. The standard statistical thermodynamic functions like heat capacity at constant pressure (Cop,m), entropy (Som) and enthalpy (Hom) were obtained from the theoretical harmonic frequencies for the optimized molecule. The nonlinear optical properties of title molecule are also addressed theoretically. Two contributions, vibrational and electronic, to the electrical properties polarizability and first order hyperpolarizability of 3Br4MSP have been evaluated using the self-consistent field wave functions within the double harmonic oscillator approximation.

Adsorption of CGA on colloidal silver particles: DFT and SERS study

NASA Astrophysics Data System (ADS)

Biswas, Nandita; Kapoor, Sudhir; Mahal, Harbir S.; Mukherjee, Tulsi

2007-08-01

Raman and surface-enhanced Raman scattering (SERS) of chlorogenic acid (CGA) have been investigated. CGA is an important plant metabolite with anti-viral and anti-bacterial properties and thus, it is useful to study its surface adsorption characteristics. The experimental Raman data is supported with DFT calculations using B3LYP functional with 6-31G ∗ and LANL2DZ basis set. This is the first report on the vibrational analysis of CGA and its silver complex. From the SERS spectra as well as theoretical calculations, it has been inferred that the molecule is chemisorbed to the silver surface through the oxygen atoms of the carboxylate group.

Theoretical searches and spectral computations of preferred conformations of various absolute configurations for a cyclodipeptide, cordycedipeptide A from the culture liquid of Cordyceps sinensis

NASA Astrophysics Data System (ADS)

Mang, Chao-Yong; Liu, Cai-Ping; Liu, Guang-Ming; Jiang, Bei; Lan, Hai; Wu, Ke-Chen; Yan, Ya; Li, Hai-Fei; Yang, Ming-Hui; Zhao, Yu

2015-02-01

A cyclic dipeptide often has the multiple configurations and the abundant conformations. The density functional theory (DFT) method is used to search the preferred conformation of the most probable configuration for cordycedipeptide A isolated from the culture liquid of Cordyceps sinensis. The time-dependent DFT approach is exploited to describe the profile of electronic circular dichroism (CD). The calculated results show that the most probable configuration is 3S6R7S, whose preferred conformation has a negative optical rotation and a positive lowest energy electronic CD band.

Physical and optical properties of DCJTB dye for OLED display applications: Experimental and theoretical investigation

NASA Astrophysics Data System (ADS)

Kurban, Mustafa; Gündüz, Bayram

2017-06-01

In this study, 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) was achieved using the experimental and theoretical studies. The electronic, optical and spectroscopic properties of DCJTB molecule were first investigated by performing experimental both solution and thin film techniques and then theoretical calculations. Theoretical results showed that one intense electronic transition is 505.26 nm a quite reasonable and agreement with the measured experimental data 505.00 and 503 nm with solution technique and film technique, respectively. Experimental and simple models were also taken into consideration to calculate the optical refractive index (n) of DCJTB molecule. The structural and electronic properties were next calculated using density functional theory (DFT) with B3LYP/6-311G (d, p) basis set. UV, FT-IR spectra characteristics and the electronic properties, such as frontier orbitals, and band gap energy (Eg) of DCJTB were also recorded time-dependent (TD) DFT approach. The theoretical Eg value were found to be 2.269 eV which is consistent with experimental results obtained from solution technique for THF solvent (2.155 eV) and literature (2.16 eV). The results herein obtained reveal that solution is simple, cost-efficient and safe for optoelectronic applications when compared with film technique.

Caprylate Salts Based on Amines as Volatile Corrosion Inhibitors for Metallic Zinc: Theoretical and Experimental Studies

PubMed Central

Valente, Marco A. G.; Teixeira, Deiver A.; Azevedo, David L.; Feliciano, Gustavo T.; Benedetti, Assis V.; Fugivara, Cecílio S.

2017-01-01

The interaction of volatile corrosion inhibitors (VCI), caprylate salt derivatives from amines, with zinc metallic surfaces is assessed by density functional theory (DFT) computer simulations, electrochemical impedance (EIS) measurements and humid chamber tests. The results obtained by the different methods were compared, and linear correlations were obtained between theoretical and experimental data. The correlations between experimental and theoretical results showed that the molecular size is the determining factor in the inhibition efficiency. The models used and experimental results indicated that dicyclohexylamine caprylate is the most efficient inhibitor. PMID:28620602

Extensive TD-DFT Benchmark: Singlet-Excited States of Organic Molecules.

PubMed

Jacquemin, Denis; Wathelet, Valérie; Perpète, Eric A; Adamo, Carlo

2009-09-08

Extensive Time-Dependent Density Functional Theory (TD-DFT) calculations have been carried out in order to obtain a statistically meaningful analysis of the merits of a large number of functionals. To reach this goal, a very extended set of molecules (∼500 compounds, >700 excited states) covering a broad range of (bio)organic molecules and dyes have been investigated. Likewise, 29 functionals including LDA, GGA, meta-GGA, global hybrids, and long-range-corrected hybrids have been considered. Comparisons with both theoretical references and experimental measurements have been carried out. On average, the functionals providing the best match with reference data are, one the one hand, global hybrids containing between 22% and 25% of exact exchange (X3LYP, B98, PBE0, and mPW1PW91) and, on the other hand, a long-range-corrected hybrid with a less-rapidly increasing HF ratio, namely LC-ωPBE(20). Pure functionals tend to be less consistent, whereas functionals incorporating a larger fraction of exact exchange tend to underestimate significantly the transition energies. For most treated cases, the M05 and CAM-B3LYP schemes deliver fairly small deviations but do not outperform standard hybrids such as X3LYP or PBE0, at least within the vertical approximation. With the optimal functionals, one obtains mean absolute deviations smaller than 0.25 eV, though the errors significantly depend on the subset of molecules or states considered. As an illustration, PBE0 and LC-ωPBE(20) provide a mean absolute error of only 0.14 eV for the 228 states related to neutral organic dyes but are completely off target for cyanine-like derivatives. On the basis of comparisons with theoretical estimates, it also turned out that CC2 and TD-DFT errors are of the same order of magnitude, once the above-mentioned hybrids are selected.

Molecular design of donor-acceptor dyes for efficient dye-sensitized solar cells I: a DFT study.

PubMed

El-Shishtawy, Reda M; Asiri, Abdullah M; Aziz, Saadullah G; Elroby, Shaaban A K

2014-06-01

Dye-sensitized solar cells (DSSCs) have drawn great attention as low cost and high performance alternatives to conventional photovoltaic devices. The molecular design presented in this work is based on the use of pyran type dyes as donor based on frontier molecular orbitals (FMO) and theoretical UV-visible spectra in combination with squaraine type dyes as an acceptor. Density functional theory has been used to investigate several derivatives of pyran type dyes for a better dye design based on optimization of absorption, regeneration, and recombination processes in gas phase. The frontier molecular orbital (FMO) of the HOMO and LUMO energy levels plays an important role in the efficiency of DSSCs. These energies contribute to the generation of exciton, charge transfer, dissociation and exciton recombination. The computations of the geometries and electronic structures for the predicted dyes were performed using the B3LYP/6-31+G** level of theory. The FMO energies (EHOMO, ELUMO) of the studied dyes are calculated and analyzed in the terms of the UV-visible absorption spectra, which have been examined using time-dependent density functional theory (TD-DFT) techniques. This study examined absorption properties of pyran based on theoretical UV-visible absorption spectra, with comparisons between TD-DFT using B3LYP, PBE, and TPSSH functionals with 6-31+G (d) and 6-311++G** basis sets. The results provide a valuable guide for the design of donor-acceptor (D-A) dyes with high molar absorptivity and current conversion in DSSCs. The theoretical results indicated 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye (D2-Me) can be effectively used as a donor dye for DSSCs. This dye has a low energy gap by itself and a high energy gap with squaraine acceptor type dye, the design that reduces the recombination and improves the photocurrent generation in solar cell.

Structure and Electronic Spectra of Purine-Methyl Viologen Charge Transfer Complexes

PubMed Central

Jalilov, Almaz S.; Patwardhan, Sameer; Singh, Arunoday; Simeon, Tomekia; Sarjeant, Amy A.; Schatz, George C.; Lewis, Frederick D.

2014-01-01

The structure and properties of the electron donor-acceptor complexes formed between methyl viologen (MV) and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV-vis and 1H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well described by time-dependent (TD) DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2′-deoxyguanosine 3′-monophosphate GMP (DAD′DAD′ type) and 7-deazaguanosine zG (DAD′ADAD′ type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors. PMID:24294996

Structure and properties of fullerene molecular crystals with linear-scaling van der Waals density functional theory

NASA Astrophysics Data System (ADS)

Mostofi, Arash; Andrinopoulos, Lampros; Hine, Nicholas

2014-03-01

Fullerene molecular crystals are of technological promise for their use in heterojunction photovoltaic cells. An improved theoretical understanding of their structure and properties would be a step towards the rational design of new devices. Simulations based on density-functional theory (DFT) are invaluable for developing such insight, but standard semi-local functionals do not capture the important inter-molecular van der Waals (vdW) interactions in fullerene crystals. Furthermore the computational cost associated with the large unit cells needed are at the limit or beyond the capabilities of traditional DFT methods. In this work we overcome these limitations by using our implementation of a number of vdW-DFs in the ONETEP linear-scaling DFT code to study the structural properties of C60 molecular crystals. Powder neutron diffraction shows that the low-temperature Pa-3 phase is orientationally ordered with individual C60 units rotated around the [111] direction. We fully explore the energy landscape associated with the rotation angle and find two stable structures that are energetically very close, one of which corresponds to the experimentally observed structure. We further consider the effect of orientational disorder in very large supercells of thousands of atoms.

Triphenylamine based organic dyes for dye sensitized solar cells: A theoretical approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohankumar, V.; Pandian, Muthu Senthil; Ramasamy, P., E-mail: ramasamyp@ssn.edu.in

2016-05-23

The geometry, electronic structure and absorption spectra for newly designed triphenylamine based organic dyes were investigated by density functional theory (DFT) and time dependent density functional theory (TD-DFT) with the Becke 3-Parameter-Lee-Yang-parr(B3LYP) functional, where the 6-31G(d,p) basis set was employed. All calculations were performed using the Gaussian 09 software package. The calculated HOMO and LUMO energies show that charge transfer occurs in the molecule. Ultraviolet–visible (UV–vis) spectrum was simulated by TD-DFT in gas phase. The calculation shows that all of the dyes can potentially be good sensitizers for DSSC. The LUMOs are just above the conduction band of TiO{sub 2}more » and their HOMOs are under the reduction potential energy of the electrolytes (I{sup −}/I{sub 3}{sup −}) which can facilitate electron transfer from the excited dye to TiO{sub 2} and charge regeneration process after photo oxidation respectively. The simulated absorption spectrum of dyes match with solar spectrum. Frontier molecular orbital results show that among all the three dyes, the “dye 3” can be used as potential sensitizer for DSSC.« less

Benchmarking fully analytic DFT force fields for vibrational spectroscopy: A study on halogenated compounds

NASA Astrophysics Data System (ADS)

Pietropolli Charmet, Andrea; Cornaton, Yann

2018-05-01

This work presents an investigation of the theoretical predictions yielded by anharmonic force fields having the cubic and quartic force constants are computed analytically by means of density functional theory (DFT) using the recursive scheme developed by M. Ringholm et al. (J. Comput. Chem. 35 (2014) 622). Different functionals (namely B3LYP, PBE, PBE0 and PW86x) and basis sets were used for calculating the anharmonic vibrational spectra of two halomethanes. The benchmark analysis carried out demonstrates the reliability and overall good performances offered by hybrid approaches, where the harmonic data obtained at the coupled cluster with single and double excitations level of theory augmented by a perturbational estimate of the effects of connected triple excitations, CCSD(T), are combined with the fully analytic higher order force constants yielded by DFT functionals. These methods lead to reliable and computationally affordable calculations of anharmonic vibrational spectra with an accuracy comparable to that yielded by hybrid force fields having the anharmonic force fields computed at second order Møller-Plesset perturbation theory (MP2) level of theory using numerical differentiation but without the corresponding potential issues related to computational costs and numerical errors.

Properties of MgO to 1.2 TPa from high-precision experiments on Sandia's Z machine and first-principles simulations using QMC and DFT

NASA Astrophysics Data System (ADS)

Shulenburger, Luke

2015-11-01

MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine the phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility a low entropy solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. The calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties requires particular care because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. Finally, understanding the behavior of MgO as the pressure releases from the Hugoniot state is a key ingredient to modeling giant impact events. We explore this regime both through additional DFT calculations and by observing the release state of the MgO into lower impedance materials. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

DFT and TD-DFT calculations of metallotetraphenylporphyrin and metallotetraphenylporphyrin fullerene complexes as potential dye sensitizers for solar cells

NASA Astrophysics Data System (ADS)

El Mahdy, A. M.; Halim, Shimaa Abdel; Taha, H. O.

2018-05-01

Density functional theory (DFT) and time-dependent DFT calculations have been employed to model metallotetraphenylporphyrin dyes and metallotetraphenylporphyrin -fullerene complexes in order to investigate the geometries, electronic structures, the density of states, non-linear optical properties (NLO), IR-vis spectra, molecular electrostatic potential contours, and electrophilicity. To calculate the excited states of the tetraphenyl porphyrin analogs, time-dependent density functional theory (TD-DFT) are used. Their UV-vis spectra were also obtained and a comparison with available experimental and theoretical results is included. The results reveal that the metal and the tertiary butyl groups of the dyes are electron donors, and the tetraphenylporphyrin rings are electron acceptors. The HOMOs of the dyes fall within the (TiO2)60 and Ti38O76 band gaps and support the issue of typical interfacial electron transfer reaction. The resulting potential drop of Mn-TPP-C60 increased by ca. 3.50% under the effect of the tertiary butyl groups. The increase in the potential drop indicates that the tertiary butyl complexes could be a better choice for the strong operation of the molecular rectifiers. The introduction of metal atom and tertiary butyl groups to the tetraphenyl porphyrin moiety leads to a stronger response to the external electric field and induces higher photo-to-current conversion efficiency. This also shifts the absorption in the dyes and makes them potential candidates for harvesting light in the entire visible and near IR region for photovoltaic applications.

Segregation formation, thermal and electronic properties of ternary cubic CdZnTe clusters: MD simulations and DFT calculations

NASA Astrophysics Data System (ADS)

Kurban, Mustafa; Erkoç, Şakir

2017-04-01

Surface and core formation, thermal and electronic properties of ternary cubic CdZnTe clusters are investigated by using classical molecular dynamics (MD) simulations and density functional theory (DFT) calculations. In this work, MD simulations of the CdZnTe clusters are performed by means of LAMMPS by using bond order potential (BOP). MD simulations are carried out at different temperatures to study the segregation phenomena of Cd, Zn and Te atoms, and deviation of clusters and heat capacity. After that, using optimized geometries obtained, excess charge on atoms, dipole moments, highest occupied molecular orbitals, lowest unoccupied molecular orbitals, HOMO-LUMO gaps (Eg) , total energies, spin density and the density of states (DOS) have been calculated with DFT. Simulation results such as heat capacity and segregation formation are compared with experimental bulk and theoretical results.

13C CPMAS NMR studies and DFT calculations of triterpene xylosides isolated from Actaea racemosa

NASA Astrophysics Data System (ADS)

Jamróz, Marta K.; Paradowska, Katarzyna; Gliński, Jan A.; Wawer, Iwona

2011-05-01

13C CPMAS NMR spectra of four triterpene glycosides: cimigenol xyloside ( 1), 26-deoxyactein ( 2), cimicifugoside H-1 ( 3) and 24-acethylhydroshengmanol xyloside ( 4) were recorded and analyzed to characterize their solid-state structure. Experimental data were supported by theoretical calculations of NMR shielding constants with the GIAO/6-31G**-su1 approach. A number of methods for the conformational search and a number of functionals for the DFT calculations were applied to ( 1). The best method was proven to be MMFF or MMFFAQ for the conformational search and the PBE1PBE functional for the DFT calculations. Extra calculations simulating C16 dbnd O⋯HOH hydrogen bond yield the isotropic shielding closer to the experimental solid-state value. For all the compounds CP kinetics parameters were calculated using either the I-S or the I-I*-S model. The analysis of CP kinetics data for methyl groups revealed differences in the T2 time constant for two methyl groups (C29 and C30) linked at C4.

Lattice and Valence Electronic Structures of Crystalline Octahedral Molybdenum Halide Clusters-Based Compounds, Cs2[Mo6X14] (X = Cl, Br, I), Studied by Density Functional Theory Calculations.

PubMed

Saito, Norio; Cordier, Stéphane; Lemoine, Pierric; Ohsawa, Takeo; Wada, Yoshiki; Grasset, Fabien; Cross, Jeffrey S; Ohashi, Naoki

2017-06-05

The electronic and crystal structures of Cs 2 [Mo 6 X 14 ] (X = Cl, Br, I) cluster-based compounds were investigated by density functional theory (DFT) simulations and experimental methods such as powder X-ray diffraction, ultraviolet-visible spectroscopy, and X-ray photoemission spectroscopy (XPS). The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. The XPS valence spectra were fairly well reproduced by simulations based on the projected electron density of states weighted with cross sections of Al K α , suggesting that DFT calculations can predict the electronic properties of metal-cluster-based crystals with good accuracy.

Hybrid-DFT  +  V w method for band structure calculation of semiconducting transition metal compounds: the case of cerium dioxide.

PubMed

Ivády, Viktor; Gali, Adam; Abrikosov, Igor A

2017-11-15

Hybrid functionals' non-local exchange-correlation potential contains a derivative discontinuity that improves on standard semi-local density functional theory (DFT) band gaps. Moreover, by careful parameterization, hybrid functionals can provide self-interaction reduced description of selected states. On the other hand, the uniform description of all the electronic states of a given system is a known drawback of these functionals that causes varying accuracy in the description of states with different degrees of localization. This limitation can be remedied by the orbital dependent exact exchange extension of hybrid functionals; the hybrid-DFT  +  V w method (Ivády et al 2014 Phys. Rev. B 90 035146). Based on the analogy of quasi-particle equations and hybrid-DFT single particle equations, here we demonstrate that parameters of hybrid-DFT  +  V w functional can be determined from approximate theoretical quasi-particle spectra without any fitting to experiment. The proposed method is illustrated on the charge self-consistent electronic structure calculation for cerium dioxide where itinerant valence states interact with well-localized 4f atomic like states, making this system challenging for conventional methods, either hybrid-DFT or LDA  +  U, and therefore allowing for a demonstration of the advantages of the proposed scheme.

Doped polycyclic aromatic hydrocarbons as building blocks for nanoelectronics: a theoretical study.

PubMed

Dral, Pavlo O; Kivala, Milan; Clark, Timothy

2013-03-01

Density functional theory (DFT) and semiempirical UHF natural orbital configuration interaction (UNO-CI) calculations are used to investigate the effect of heteroatom substitution at the central position of a model polycyclic aromatic hydrocarbon. The effects of the substitution on structure, strain, electronic and spectral properties, and aromaticity of the compounds are discussed.

Spectral and structural studies of the anti-cancer drug Flutamide by density functional theoretical method

NASA Astrophysics Data System (ADS)

Mariappan, G.; Sundaraganesan, N.

2014-01-01

A comprehensive screening of the more recent DFT theoretical approach to structural analysis is presented in this section of theoretical structural analysis. The chemical name of 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide is usually called as Flutamide (In the present study it is abbreviated as FLT) and is an important and efficacious drug in the treatment of anti-cancer resistant. The molecular geometry, vibrational spectra, electronic and NMR spectral interpretation of Flutamide have been studied with the aid of density functional theory method (DFT). The vibrational assignments of the normal modes were performed on the basis of the PED calculations using the VEDA 4 program. Comparison of computational results with X-ray diffraction results of Flutamide allowed the evaluation of structure predictions and confirmed B3LYP/6-31G(d,p) as accurate for structure determination. Application of scaling factors for IR and Raman frequency predictions showed good agreement with experimental values. This is supported the assignment of the major contributors of the vibration modes of the title compound. Stability of the molecule arising from hyperconjugative interactions leading to its bioactivity, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. NMR chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. The comparison of measured FTIR, FT-Raman, and UV-Visible data to calculated values allowed assignment of major spectral features of the title molecule. Besides, Frontier molecular orbital analyze was also investigated using theoretical calculations.

A computational perspective of vibrational and electronic analysis of potential photosensitizer 2-chlorothioxanthone

NASA Astrophysics Data System (ADS)

Ali, Narmeen; Mansha, Asim; Asim, Sadia; Zahoor, Ameer Fawad; Ghafoor, Sidra; Akbar, Muhammad Usman

2018-03-01

This paper deals with combined theoretical and experimental study of geometric, electronic and vibrational properties of 2-chlorothioxanthone (CTX) molecule which is potential photosensitizer. The FT-IR spectrum of CTX in solid phase was recorded in 4000-400 cm-1 region. The UV-Vis. absorption spectrum was also recorded in the laboratory as well as computed at DFT/B3LYP level in five different phases viz. gas, water, DMSO, acetone and ethanol. The quantum mechanics based theoretical IR and Raman spectra were also calculated for the title compound employing HF and DFT functional with 3-21G+, 6-31G+ and 6-311G+, 6-311G++ basis sets, respectively, and assignment of each vibrational frequency has been done on the basis of potential energy distribution (PED). A comparison has been made between theoretical and experimental vibrational spectra as well as for the UV-Vis. absorption spectra. The computed infra red & Raman spectra by DFT compared with experimental spectra along with reliable vibrational assignment based on PED. The calculated electronic properties, results of natural bonding orbital (NBO) analysis, charge distribution, dipole moment and energies have been reported in the paper. Bimolecular quenching of triplet state of CTX in the presence of triethylamine, 2-propanol triethylamine and diazobicyclooctane (DABCO) reflect the interactions between them. The bimolecular quenching rate constant is fastest for interaction of 3CTX in the presence of DABCO reflecting their stronger interactions.

Applications of the Conceptual Density Functional Theory Indices to Organic Chemistry Reactivity.

PubMed

Domingo, Luis R; Ríos-Gutiérrez, Mar; Pérez, Patricia

2016-06-09

Theoretical reactivity indices based on the conceptual Density Functional Theory (DFT) have become a powerful tool for the semiquantitative study of organic reactivity. A large number of reactivity indices have been proposed in the literature. Herein, global quantities like the electronic chemical potential μ, the electrophilicity ω and the nucleophilicity N indices, and local condensed indices like the electrophilic P k + and nucleophilic P k - Parr functions, as the most relevant indices for the study of organic reactivity, are discussed.

Theoretical NMR and conformational analysis of solvated oximes for organophosphates-inhibited acetylcholinesterase reactivation

NASA Astrophysics Data System (ADS)

da Silva, Jorge Alberto Valle; Modesto-Costa, Lucas; de Koning, Martijn C.; Borges, Itamar; França, Tanos Celmar Costa

2018-01-01

In this work, quaternary and non-quaternary oximes designed to bind at the peripheral site of acetylcholinesterase previously inhibited by organophosphates were investigated theoretically. Some of those oximes have a large number of degrees of freedom, thus requiring an accurate method to obtain molecular geometries. For this reason, the density functional theory (DFT) was employed to refine their molecular geometries after conformational analysis and to compare their 1H and 13C nuclear magnetic resonance (NMR) theoretical signals in gas-phase and in solvent. A good agreement with experimental data was achieved and the same theoretical approach was employed to obtain the geometries in water environment for further studies.

Synthesis, XRD crystal structure, spectroscopic characterization (FT-IR, 1H and 13C NMR), DFT studies, chemical reactivity and bond dissociation energy studies using molecular dynamics simulations and evaluation of antimicrobial and antioxidant activities of a novel chalcone derivative, (E)-1-(4-bromophenyl)-3-(4-iodophenyl)prop-2-en-1-one

NASA Astrophysics Data System (ADS)

Zainuri, D. Alwani; Arshad, Suhana; Khalib, N. Che; Razak, I. Abdul; Pillai, Renjith Raveendran; Sulaiman, S. Fariza; Hashim, N. Shafiqah; Ooi, K. Leong; Armaković, Stevan; Armaković, Sanja J.; Panicker, C. Yohannan; Van Alsenoy, C.

2017-01-01

In the present study, the title compound named as (E)-1-(4-bromophenyl)-3-(4-iodophenyl)prop-2-en-1-one was synthesized and structurally characterized by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic system with P21/c space group with the unit cell parameters of a = 16.147 (2) Å, b = 14.270 (2) Å, c = 5.9058 (9) Å, β = 92.577 (3)° and Z = 4. The molecular geometry obtained from X-Ray structure determination was optimized by Density Functional Theory (DFT) using B3LYP/6-31G+(d, p)/Lanl2dz(f) method in the ground state. The IR spectrum was recorded and interpreted in details with the aid of Density Functional Theory (DFT) calculations and Potential Energy Distribution (PED) analysis. In order to investigate local reactivity properties of the title molecule, we have conducted DFT calculations of average local ionization energy surface and Fukui functions which were mapped to the electron density surface. In order to predict the open air stability and possible degradation properties, within DFT approach, we have also calculated bond dissociation energies. 1H and 13C NMR spectra were recorded and chemical shifts were calculated theoretically and compared with the experimental values. In addition, in vitro antimicrobial results show that the title compound has great potential of antibacterial activity against Staphylococcus aureus, Staphylococcus epidermidis and Micrococcus luteus bacteria and antifungal activity against Candida albicans in comparison to some reported chalcone derivatives. Antioxidant studies revealed the highest metal chelating activity of this compound.

Theoretical Investigation of the Electronic Structure of Fe(II) Complexes at Spin-State Transitions

PubMed Central

2013-01-01

The electronic structure relevant to low spin (LS)↔high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+ (1) (tz = 1H-tetrazole), [Fe(bipy)3]2+ (2) (bipy = 2,2′-bipyridine), and [Fe(terpy)2]2+ (3) (terpy = 2,2′:6′,2″-terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT), and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS–HS states (ΔEHL) applying the above methods and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔEHL. In addition, a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves. Although the TD-DFT results might differ in some respect (in our case, we found a discrepancy at the triplet states), our results suggest that this approach, with due care, is very promising as an alternative for the very expensive CASPT2 method. Finally, the two-dimensional (2D) potential energy surfaces above the plane spanned by the two relevant configuration coordinates in [Fe(terpy)2]2+ were computed at both the DFT and CASPT2 levels. These 2D surfaces indicate that the singlet–triplet and triplet–quintet states are separated along different coordinates, i.e., different vibration modes. Our results confirm that in contrast to the case of complexes with mono- and bidentate ligands, the singlet–quintet transitions in [Fe(terpy)2]2+ cannot be described using a single configuration coordinate. PMID:25821416

How Does Lithiation Affect Electro-Optical Features of Corannulene (C20H10) and Quadrannulene (C16H8) Buckybowls?

NASA Astrophysics Data System (ADS)

Shakerzadeh, Ehsan; Kazemimoghadam, Fatemeh; Anota, Ernesto Chigo

2018-04-01

The influence of lithiation process on the HOMO-LUMO gap and the first hyperpolarizability values of corannulene (C20H10) and quadrannulene (C16H8) buckybowls are investigated using density functional theory (DFT) calculations. Lithiation is performed at the bridging position of the C-C bond of benzene rings of quadrannulene and corannulene. The HOMO-LUMO gap of lithiated buckybowls is reduced with respect to pristine ones. The results indicate that the lithiation process causes the remarkable enhancement of the first hyperpolarizability. The time-dependent density functional theory (TD-DFT) calculations are also performed to understand how lithiation affects the first hyperpolarizability values. The present results might be valuable for further theoretical and experimental studies on the electronic and nonlinear optical properties of buckybowl compounds.

Molecular design and theoretical characterization of benzodithiophene based organic photovoltaic materials

NASA Astrophysics Data System (ADS)

Bhattacharya, Labanya; Sahu, Sridhar

2018-05-01

Two different oligomers, containing methyl substituted Benzodithiophene (BDT) as donor unit, fluorinated thiophene as the π-bridge unit and two different kinds of acceptors based on fluorinated benzothiadiazole, fluorinated benzoselenadiazole units are designed for bulk heterojunction (BHJ) organic solar cell (OSC). The ground and excited state properties of those donor-π-acceptor-π-donor (D-π-A-π-D) oligomeric configurations are characterized via density functional (DFT) and time dependent density functional theory (TD-DFT). The parameters such as dipole moment (ρ), chemical potential (µ), electronegativity (χ), frontier molecular orbital (FMO) analysis, HOMO-LUMO gap, open circuit voltage (Voc) and driving force (ΔE) are calculated to analyze geometrical, electronic structural, quantum chemical and photovoltaic properties of the compounds. In addition, optical absorption spectra are also presented for the optical characterization of the compounds.

Real-Space Multiple-Scattering Theory and Its Applications at Exascale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eisenbach, Markus; Wang, Yang

In recent decades, the ab initio methods based on density functional theory (DFT) (Hohenberg and Kohn 1964, Kohn and Sham 1965) have become a widely used tool in computational materials science, which allows theoretical prediction of physical properties of materials from the first principles and theoretical interpretation of new physical phenomena found in experiments. In the framework of DFT, the original problem that requires solving a quantum mechanical equation for a many-electron system is reduced to a one-electron problem that involves an electron moving in an effective field, while the effective field potential is made up of an electrostatic potential,more » also known as Hartree potential, arising from the electronic and ion charge distribution in space and an exchange–correlation potential, which is a function of the electron density and encapsulates the exchange and correlation effects of the many-electron system. Even though the exact functional form of the exchange-correlation potential is formally unknown, a local density approximation (LDA) or a generalized gradient approximation (GGA) is usually applied so that the calculation of the exchange–correlation potential, as well as the exchange–correlation energy, becomes tractable while a required accuracy is retained. Based on DFT, ab initio electronic structure calculations for a material generally involve a self-consistent process that iterates between two computational tasks: (1) solving an one-electron Schrödinger equation, also known as Kohn–Sham equation, to obtain the electron density and, if needed, the magnetic moment density, and (2) solving the Poisson equation to obtain the electrostatic potential corresponding to the electron density and constructing the effective potential by adding the exchange–correlation potential to the electrostatic potential. This self-consistent process proceeds until a convergence criteria is reached.« less

Vibrational spectra, optical properties, NBO and HOMO-LUMO analysis of L-Phenylalanine L-Phenylalaninium Perchlorate: DFT calculations

NASA Astrophysics Data System (ADS)

Elleuch, Nabil; Ben Ahmed, Ali; Feki, Habib; Abid, Younes; Minot, Christian

2014-03-01

In this work, we report a combined experimental and theoretical study of a nonlinear optical material, L-Phenylalanine L-Phenylalaninium Perchlorate. Single crystals of the title compound have been grown by slow evaporation of an aqueous solution at room temperature. Theoretical calculations were preceded by redetermination of the crystal X-ray structure. The compound crystallizes in the non-centro symmetric space group P212121 of the orthorhombic system. The FT-IR and Raman spectra of the crystal were recorded and analyzed. The density functional theory (DFT) computations have been performed at B3LYP/6-31G(d) level to derive equilibrium geometry, vibrational wavenumbers, intensity and NLO properties. All observed vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our DFT calculations as a primary source of attribution and also by comparison with the previous results for similar compounds. Natural bond orbital analysis was carried out to demonstrate the various inter-and intramolecular interaction that are responsible of the stabilization of the compound. The lowering of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gap appears to be the cause of its enhanced charge transfer interaction leading to high NLO activity.

Effect of tellurium concentration on the structural, electronic and mechanical properties of beryllium sulphide: A DFT approach

NASA Astrophysics Data System (ADS)

Iyorzor, B. E.; Babalola, M. I.; Adetunji, B. I.; Bakare, F. O.

2018-05-01

The structural, electronic and mechanical properties of Be{S}1-xT{e}x are studied within the concentration range of 0≤slant x≤slant 1 using first-principles plane–wave Pseudopotential density functional theory (DFT) approach. We have used generalized gradient approximation (GGA) to treat the exchange-correlation potentials. The elastic constants, bulk, shear and Young’s moduli, Poisson’s ratio, and Zener’s anisotropic factors are calculated. The results were found to be in agreement with other available theoretical and experimental values. It was also observed that the existence and increase of Tellurium concentration decreases the hardness of the alloy.

Theoretical searches and spectral computations of preferred conformations of various absolute configurations for a cyclodipeptide, cordycedipeptide A from the culture liquid of Cordyceps sinensis.

PubMed

Mang, Chao-Yong; Liu, Cai-Ping; Liu, Guang-Ming; Jiang, Bei; Lan, Hai; Wu, Ke-Chen; Yan, Ya; Li, Hai-Fei; Yang, Ming-Hui; Zhao, Yu

2015-02-05

A cyclic dipeptide often has the multiple configurations and the abundant conformations. The density functional theory (DFT) method is used to search the preferred conformation of the most probable configuration for cordycedipeptide A isolated from the culture liquid of Cordyceps sinensis. The time-dependent DFT approach is exploited to describe the profile of electronic circular dichroism (CD). The calculated results show that the most probable configuration is 3S6R7S, whose preferred conformation has a negative optical rotation and a positive lowest energy electronic CD band. Copyright © 2014 Elsevier B.V. All rights reserved.

Naphtyl- and pyrenyl-flavylium dyads: Synthesis, DFT and optical properties

NASA Astrophysics Data System (ADS)

Aguilar-Castillo, Bethsy Adriana; Sánchez-Bojorge, Nora Aydee; Chávez-Flores, David; Camacho-Dávila, Alejandro A.; Pasillas-Ornelas, Eddie; Rodríguez-Valdez, Luz-María; Zaragoza-Galán, Gerardo

2018-03-01

A one-step preparation of flavylium salts containing naphtyl and pyrenyl moieties is described hereafter. Flavylium salts were successfully characterized by 1H NMR spectroscopy and ESI-MS spectrometry. Theoretical calculations were carried out by means of Density Functional Theory in order to simulate flavylium cation electronic transitions. Molecular simulation of -naphtyl derivatives displayed a coplanar conformation between naphthalene and benzopyrylium moieties. In contrast, DFT analysis exhibited a non-coplanar arrangement of pyrene and benzopyrylium units. These former statements in coherence with the absorption experiments where the naphtyl-flavylium dyads shows a red-shifted maximum absorption band with respect to pyrene dyads, led us to conclude that these bathochromic effects are associated with a more planar conformation.

Probing the adsorption mechanism in thiamazole bound to the silver surface with Surface-enhanced Raman Scattering and DFT

NASA Astrophysics Data System (ADS)

Biswas, Nandita; Thomas, Susy; Sarkar, Anjana; Mukherjee, Tulsi; Kapoor, Sudhir

2009-09-01

Surface-enhanced Raman scattering (SERS) of thiamazole have been investigated in aqueous solution. Thiamazole is an important anti-thyroid drug that is used in the treatment of hyperthyroidism (over activity of the thyroid gland). Due to its medicinal importance, the surface adsorption properties of thiamazole have been studied. The experimental Raman and SERS data are supported with DFT calculations using B3LYP functional with LANL2DZ basis set. From the SERS spectra as well as theoretical calculations, it has been inferred that thiamazole is chemisorbed to the silver surface directly through the sulphur atom and the ring N atom, with a tilted orientation.

Spin localization, magnetic ordering, and electronic properties of strongly correlated Ln2O3 sesquioxides (Ln=La, Ce, Pr, Nd)

NASA Astrophysics Data System (ADS)

El-Kelany, Kh. E.; Ravoux, C.; Desmarais, J. K.; Cortona, P.; Pan, Y.; Tse, J. S.; Erba, A.

2018-06-01

Lanthanide sesquioxides are strongly correlated materials characterized by highly localized unpaired electrons in the f band. Theoretical descriptions based on standard density functional theory (DFT) formulations are known to be unable to correctly describe their peculiar electronic and magnetic features. In this study, electronic and magnetic properties of the first four lanthanide sesquioxides in the series are characterized through a reliable description of spin localization as ensured by hybrid functionals of the DFT, which include a fraction of nonlocal Fock exchange. Because of the high localization of the f electrons, multiple metastable electronic configurations are possible for their ground state depending on the specific partial occupation of the f orbitals: the most stable configuration is here found and characterized for all systems. Magnetic ordering is explicitly investigated, and the higher stability of an antiferromagnetic configuration with respect to the ferromagnetic one is predicted. The critical role of the fraction of exchange on the description of their electronic properties (notably, on spin localization and on the electronic band gap) is addressed. In particular, a recently proposed theoretical approach based on a self-consistent definition—through the material dielectric response—of the optimal fraction of exchange in hybrid functionals is applied to these strongly correlated materials.

Theoretical and experimental investigations of optical, structural and electronic properties of the lower-dimensional hybrid [NH3-(CH2)10-NH3]ZnCl4

NASA Astrophysics Data System (ADS)

El Mrabet, R.; Kassou, S.; Tahiri, O.; Belaaraj, A.; Guionneau, P.

2016-10-01

In the current study, a combination between theoretical and experimental studies has been made for the hybrid perovskite [NH3-(CH2)10-NH3]ZnCl4. The density functional theory (DFT) was performed to investigate structural and electronic properties of the tilted compound. A local approximation (LDA) and semi-local approach (GGA) were employed. The results are obtained using, respectively, the local exchange correlation functional of Perdew-Wang 92 (PW92) and semi local functional of Perdew-Burke-Ernzerhof (PBE). The optimized cell parameters are in good agreement with the experimental results. Electronic properties have been studied through the calculation of band structures and density of state (DOS), while structural properties are investigated by geometry optimization of the cell. Fritz-Haber-Institute (FHI) pseudopotentials were employed to perform all calculations. The optical diffuse reflectance spectra was mesured and applied to deduce the refractive index ( n), the extinction coefficient ( k), the absorption coefficient (α), the real and imaginary dielectric permittivity parts (ɛr,ɛi)) and the optical band gap energy Eg. The optical band gap energy value shows good consistent with that obtained from DFT calculations and reveals the insulating behavior of the material.

Time dependent-density functional theory (TD-DFT) and experimental studies of UV-Visible spectra and cyclic voltammetry for Cu(II) complex with Et2DTC

NASA Astrophysics Data System (ADS)

Valle, Eliana Maira A.; Maltarollo, Vinicius Gonçalves; Almeida, Michell O.; Honorio, Kathia Maria; dos Santos, Mauro Coelho; Cerchiaro, Giselle

2018-04-01

In this work, we studied the complexation mode between copper(II) ion and the specific ligand investigated as carriers of metals though biological membranes, diethyldithiocarbamate (Et2DTC). It is important to understand how this occurs because it is an important intracellular chelator with potential therapeutic applications. Theoretical and experimental UV visible studies were performed to investigate the complexation mode between copper and the ligand. Electrochemical studies were also performed to complement the spectroscopic analyses. According to the theoretical calculations, using TD-DFT (Time dependent density functional theory), with B3LYP functional and DGDVZP basis set, implemented in Gaussian 03 package, it was observed that the formation of the complex [Cu(Et2DTC)2] is favorable with higher electron density over the sulfur atoms of the ligand. UV/Vis spectra have a charge transfer band at 450 nm, with the DMSO-d6 band shift from 800 to 650 nm. The electrochemical experiments showed the formation of a new redox process, referring to the complex, where the reduction peak potential of copper is displaced to less positive region. Therefore, the results obtained from this study give important insights on possible mechanisms involved in several biological processes related to the studied system.

Catalytic Hydrogenation of Carbon Dioxide with Ammonia-Borane by Pincer-type Phosphorus Compound: A Theoretical Prediction.

PubMed

Zeng, Guixiang; Maeda, Satoshi; Taketsugu, Tetsuya; Sakaki, Shigeyoshi

2016-10-01

Theoretically designed pincer-type phosphorus compound is found to be active for the hydrogenation of carbon dioxide (CO 2 ) with ammonia-borane. DFT, ONIOM(CCSD(T):MP2), and CCSD(T) computational results demonstrated that the reaction occurs through the phosphorus-ligand cooperative catalysis function, which provides an unprecedented protocol for metal-free CO 2 conversion. The phosphorus compounds with the NNN ligand are more active than those with the ONO ligand. The conjugate and planar ligand considerably improves the efficiency of the catalyst.

Experimental FT-IR, Laser-Raman and DFT spectroscopic analysis of a potential chemotherapeutic agent 6-(2-methylpropyl)-4-oxo-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carbonitrile.

PubMed

Sert, Yusuf; Al-Turkistani, Abdulghafoor A; Al-Deeb, Omar A; El-Emam, Ali A; Ucun, Fatih; Çırak, Çağrı

2014-01-01

In this study, the experimental and theoretical vibrational frequencies of a newly synthesized potential chemotherapeutic agent namely, 6-(2-methylpropyl)-4-oxo-2-sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carbonitrile have been investigated. The experimental FT-IR (4000-400 cm(-1)) and Laser-Raman spectra (4000-100 cm(-1)) of the molecule in solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 09 W software, for the first time. The assignments of the vibrational frequencies have been done by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with the results in the literature. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and depicted. Copyright © 2013 Elsevier B.V. All rights reserved.

Synthesis, structural characterization and comparison of experimental and theoretical results by DFT level of molecular structure of 4-(4-methoxyphenethyl)-3,5-dimethyl-4H-1,2,4-triazole.

PubMed

Düğdü, Esra; Ünver, Yasemin; Ünlüer, Dilek; Tanak, Hasan; Sancak, Kemal; Köysal, Yavuz; Işık, Şamil

2013-05-01

4-(4-Methoxyphenethyl)-3,5-dimethyl-4H-1,2,4-triazole (3) was synthesized from the reaction of ethyl N'-acetylacetohydrazonate (1) with 2-(4-methoxyphenyl)ethanamine (2). The structure of the title compound 3 has been inferred through IR, (1)H/(13)C NMR, mass spectrometry, elemental analyses and combination of X-ray crystallography and theoretical methods. In addition to the molecular geometry from X-ray determination, the molecular geometry and vibrational frequencies of the title compound 3 in the ground state, were calculated using the density functional method (B3LYP) with the 6-31G(d) basis set. The calculated results show that the optimized geometry can well reproduce the crystal structure and the theoretical vibrational frequencies show good agreement with experimental values. The nonlinear optical properties are also addressed theoretically. The predicted nonlinear optical properties of 3 are greater than ones of urea. In addition, DFT calculations of molecular electrostatic potentials and frontier molecular orbitals of the title compound were carried out at the B3LYP/6-31G(d) level of theory. Copyright © 2012. Published by Elsevier B.V.

Vibrational spectroscopy and theoretical studies on 2,4-dinitrophenylhydrazine

NASA Astrophysics Data System (ADS)

Chiş, V.; Filip, S.; Miclăuş, V.; Pîrnău, A.; Tănăselia, C.; Almăşan, V.; Vasilescu, M.

2005-06-01

In this work, we will report a combined experimental and theoretical study on molecular and vibrational structure of 2,4-dinitrophenylhydrazine. FT-IR, FT-IR/ATR and Raman spectra of normal and deuterated DNPH have been recorded and analyzed in order to get new insights into molecular structure and properties of this molecule, with particular emphasize on its intra- and intermolecular hydrogen bonds (HB's). For computational purposes we used density functional theory (DFT) methods, with B3LYP and BLYP exchange-correlation functionals, in conjunction with 6-31G(d) basis set. All experimental vibrational bands have been discussed and assigned to normal modes on the basis of DFT calculations and isotopic shifts and by comparison to other dinitro- substituted compounds [V. Chiş, Chem. Phys., 300 (2004) 1]. To aid in mode assignments, we based on the direct comparison between experimental and calculated spectra by considering both the frequency sequence and the intensity pattern of the experimental and computed vibrational bands. It is also shown that semiempirical AM1 method predicts geometrical parameters and vibrational frequencies related to the HB in a pleasant agreement with experiment, being surprisingly accurate from this perspective.

Ab initio study for the IR spectroscopy of PbTiO3 and PbZrO3, primary blocks of PbZr1‑x Ti x O3

NASA Astrophysics Data System (ADS)

Peperstraete, Yoann; Amzallag, Emilie; Tétot, Robert; Roy, Pascale

2018-05-01

PbTiO3 (PT) and PbZrO3 (PZ) are the two primary blocks of the solid solution PbZr1‑x Ti x O3 (PZT). They can be modelled in different ways; but, in order to do comparable DFT calculations on PZT, with different values of x, one must find a unique method that can be used for both PT and PZ. In particular, we want to evaluate their vibrational properties to compare them with experimental data. Density functional theory (DFT) is used to perform structure geometry optimizations and electronic structure calculations, both on low- and high-temperature phase. Then, harmonic vibrational frequencies of their low-temperature phase are determined for transverse and longitudinal optical (TO & LO) phonons. Moreover, a detailed study of the eigenvectors shows that accurate calculations are necessary to correctly interpret and understand the IR spectra. In the end, the comparison of our theoretical results with previous experimental and theoretical data confirm the strong potential of the SOGGA (second-order generalized gradient approximation) functional to correctly describe PT, PZ and, hopefully, PZT; especially their structural and vibrational properties.

Vibrational and UV spectroscopic studies of 2-coumaranone by experimental and density functional theory calculations

NASA Astrophysics Data System (ADS)

Priya, Y. Sushma; Rao, K. Ramachandra; Chalapathi, P. V.; Satyavani, M.; Veeraiah, A.

2017-09-01

The vibrational and electronic properties of 2-coumaranone have been reported in the ground state using experimental techniques (FT-IR, FT-Raman, UV spectra and fluorescence microscopic imaging) and density functional theory (DFT) employing B3LYP correlation with the 6-31G(d, p) basis set. The theoretically reported optimized parameters, vibrational frequencies etc., were compared with the experimental values, which yielded good concurrence between the experimental and calculated values. The assignments of the vibrational spectra were done with the help of normal co-ordinate analysis (NCA) following the Scaled Quantum Mechanical Force Field(SQMFF) methodology. The whole assignments of fundamental modes were based on the potential energy distribution (PED) matrix. The electric dipole moment and the first order hyperpolarizability of the 2-coumaranone have been computed using quantum mechanical calculations. NBO and HOMO, LUMO analyses have been carried out. UV spectrum of 2-coumaranone was recorded in the region 100-300 nm and compared with the theoretical UV spectrum using TD-DFT and SAC-CI methods by which a good agreement is observed. Fluorescence microscopic imaging study reflects that the compound fluoresces in the green-yellow region.

Nano Cu interaction with single amino acid tyrosine derived self-assemblies; study through XRD, AFM, confocal Raman microscopy, SERS and DFT methods

NASA Astrophysics Data System (ADS)

Govindhan, Raman; Karthikeyan, Balakrishnan

2017-12-01

3,5-Bis(trifluoromethyl)benzylamine derivatives of single amino acid tyrosine produced self-assembled nanotubes (BTTNTs) as simple Phe-Phe. It has been observed that tyrosine derivative gives exclusively micro and nano tubes irrespective of the concentration of the precursor monomer. However, the introduced xenobiotic trifluoromethyl group (TFM) present in key backbone positionsof the self assembly gives the specific therapeutic function has been highlighted. Herein this work study of such self assembled nanotubes were studied through experimental and theoretical methods. The interaction of nanocopper cluster with the nanotubes (Cu@BTTNTs) were extensively studied by various methods like XRD, AFM, confocal Raman microscopy, SERS and theoretical methods like Mulliken's atomic charge analysis. SERS reveals that the interactions of Cu cluster with NH2, OH, NH and phenyl ring π-electrons system of BTTNTs. DFT studies gave the total dipole moment values of Cu@BTTNTs and explained the nature of interaction.

Experimental and DFT studies of (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline: electronic and vibrational properties.

PubMed

Sun, Wenqi; Yuan, Guozan; Liu, Jingxin; Ma, Li; Liu, Chengbu

2013-04-01

The title molecule (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline (DPEQ) was synthesized and characterized by FT-IR, UV-vis, NMR spectroscopy. The molecular geometry, vibrational frequencies and gauge independent atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the compound in the ground state have been calculated by using the density functional theory (DFT) method. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. The calculated results indicate that the theoretical vibrational frequencies, 1H and 13C NMR chemical shift values show good agreement with experimental data. The electronic properties like UV-vis spectral analysis and HOMO-LUMO analysis of DPEQ have been reported and compared with experimental data. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP). Copyright © 2013 Elsevier B.V. All rights reserved.

Experimental and DFT studies of (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline: Electronic and vibrational properties

NASA Astrophysics Data System (ADS)

Sun, Wenqi; Yuan, Guozan; Liu, Jingxin; Ma, Li; Liu, Chengbu

2013-04-01

The title molecule (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline (DPEQ) was synthesized and characterized by FT-IR, UV-vis, NMR spectroscopy. The molecular geometry, vibrational frequencies and gauge independent atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the compound in the ground state have been calculated by using the density functional theory (DFT) method. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. The calculated results indicate that the theoretical vibrational frequencies, 1H and 13C NMR chemical shift values show good agreement with experimental data. The electronic properties like UV-vis spectral analysis and HOMO-LUMO analysis of DPEQ have been reported and compared with experimental data. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP).

A quantitative analysis of weak intermolecular interactions & quantum chemical calculations (DFT) of novel chalcone derivatives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chavda, Bhavin R., E-mail: chavdabhavin9@gmail.com; Dubey, Rahul P.; Patel, Urmila H.

The novel chalcone derivatives have widespread applications in material science and medicinal industries. The density functional theory (DFT) is used to optimized the molecular structure of the three chalcone derivatives (M-I, II, III). The observed discrepancies between the theoretical and experimental (X-ray data) results attributed to different environments of the molecules, the experimental values are of the molecule in solid state there by subjected to the intermolecular forces, like non-bonded hydrogen bond interactions, where as isolated state in gas phase for theoretical studies. The lattice energy of all the molecules have been calculated using PIXELC module in Coulomb –London –Paulimore » (CLP) package and is partitioned into corresponding coulombic, polarization, dispersion and repulsion contributions. Lattice energy data confirm and strengthen the finding of the X-ray results that the weak but significant intermolecular interactions like C-H…O, Π- Π and C-H… Π plays an important role in the stabilization of crystal packing.« less

A theoretical study of a series of water-soluble triphenylamine photosensitizers for two-photon photodynamic therapy.

PubMed

Wang, Xin; Yin, Xue; Lai, Xiao-Yong; Liu, Ying-Tao

2018-10-05

In this study, the therapeutic activity of a series of water-soluble triphenylamine (TP) photosensitizers (Ps) was explored by using theoretical simulations. The key photophysical parameters which determined the efficiency of Ps, such as absorption electronic spectra, singlet-triplet energy gaps and spin-orbit matrix elements were calculated at density functional theory and its time-dependent extension (DFT, TD-DFT). The calculated results showed that these TP photosensitizers possessed large two-photon absorption cross-section in the near-infrared region (NIR), efficient intersystem crossing (ISC) transition from the first singlet excited state to the low lying triplet excited states and sufficient energy for generating reactive oxygen species (ROS). These suitable features made these TP series holding great promise for applications in two-photon photodynamic therapy (PDT). These TP photosensitizers studied here in principle extended the application range of two-photon PDT in water solution. Copyright © 2018 Elsevier B.V. All rights reserved.

Molecular structure and vibrational spectra of Bis(melaminium) terephthalate dihydrate: A DFT computational study

NASA Astrophysics Data System (ADS)

Tanak, Hasan; Marchewka, Mariusz K.; Drozd, Marek

2013-03-01

The experimental and theoretical vibrational spectra of Bis(melaminium) terephthalate dihydrate were studied. The Fourier transform infrared (FT-IR) spectra of the Bis(melaminium) terephthalate dihydrate and its deuterated analogue were recorded in the solid phase. The molecular geometry and vibrational frequencies of Bis(melaminium) terephthalate dihydrate in the ground state have been calculated by using the density functional method (B3LYP) with 6-31++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The molecule contains the weak hydrogen bonds of Nsbnd H⋯O, Nsbnd H⋯N and Osbnd H⋯O types, and those bonds are calculated with DFT method. In addition, molecular electrostatic potential, frontier molecular orbitals and natural bond orbital analysis of the title compound were investigated by theoretical calculations. The lack of the second harmonic generation (SHG) confirms the presence of macroscopic center of inversion.

Molecular structure and vibrational spectra of Bis(melaminium) terephthalate dihydrate: a DFT computational study.

PubMed

Tanak, Hasan; Marchewka, Mariusz K; Drozd, Marek

2013-03-15

The experimental and theoretical vibrational spectra of Bis(melaminium) terephthalate dihydrate were studied. The Fourier transform infrared (FT-IR) spectra of the Bis(melaminium) terephthalate dihydrate and its deuterated analogue were recorded in the solid phase. The molecular geometry and vibrational frequencies of Bis(melaminium) terephthalate dihydrate in the ground state have been calculated by using the density functional method (B3LYP) with 6-31++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The molecule contains the weak hydrogen bonds of N-H···O, N-H···N and O-H···O types, and those bonds are calculated with DFT method. In addition, molecular electrostatic potential, frontier molecular orbitals and natural bond orbital analysis of the title compound were investigated by theoretical calculations. The lack of the second harmonic generation (SHG) confirms the presence of macroscopic center of inversion. Copyright © 2012 Elsevier B.V. All rights reserved.

Franck Condon shift assessment in 2D MoS₂.

PubMed

Gupta, Sunny; Shirodkar, Sharmila N; Kaplan, Daniel; Swaminathan, Venkataraman; Yakobson, Boris I

2018-01-19

Optical spectroscopy (OS) techniques are often coupled with first-principles density functional theoretical (DFT) calculations for determining the precise influence of defects on the electronic and structural properties of two dimensional (2D) TMDs. Such calculations are carried out presuming there is little or no effect of vibrational transitions on the observed electronic spectrum. However, if the effect of change in vibrational energy [Franck Condon (FC) shift] associated with such a transition is large, it could possibly lead to a different origin for the observed peak. One such instance is the attribution of the 0.75 eV cathodoluminescence peak by Fabbri et. al. [Nat. Commun. 7, 13044 (2016)]. to an optical transition from an S vacancy level in the band gap, under the assumption that the FC shift is negligible. Here, by first principles constrained DFT calculations using hybrid HSE06 functional we show that this combined prediction of OS and DFT calculations is valid for 2D MoS2 since the FC shift associated with electronic transitions from a sulfur vacancy is, indeed, small ~28 meV. Based on our calculations we conclude that it is reasonable to make a direct connection between DFT calculations and optical spectroscopy techniques in this material, hence, establishing a one to one relation between defect related emission bands and electronic transitions from the defect levels. © 2018 IOP Publishing Ltd.

Molecular structure, vibrational spectra, AIM, HOMO-LUMO, NBO, UV, first order hyperpolarizability, analysis of 3-thiophenecarboxylic acid monomer and dimer by Hartree-Fock and density functional theory

NASA Astrophysics Data System (ADS)

Issaoui, Noureddine; Ghalla, Houcine; Muthu, S.; Flakus, H. T.; Oujia, Brahim

2015-02-01

In this work, the molecular structure, harmonic vibrational frequencies, UV, NBO and AIM of 3-thiophenecarboxilic acid (abbreviated as 3-TCA) monomer and dimer has been investigated. The FT-IR and FT-Raman spectra were recorded. The ground-state molecular geometry and vibrational frequencies have been calculated by using the Hartree-Fock (HF) and density functional theory (DFT)/B3LYP methods and 6-311++G(d,p) as a basis set. The fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with VEDA program. Comparison of the observed fundamental vibrational frequencies of 3-TCA with calculated results by HF and DFT methods indicates that B3LYP is better to HF method for molecular vibrational problems. The difference between the observed and scaled wavenumber values is very small. The theoretically predicted FT-IR and FT-Raman spectra of the title compound have been constructed. A study on the Mulliken atomic charges, the electronic properties were performed by time-dependent DFT (TD-DFT) approach, frontier molecular orbitals (HOMO-LUMO), molecular electrostatic potential (MEP) and thermodynamic properties have been performed. The electric dipole moment (μ) and the first hyperpolarizability (β) values of the investigated molecule have been also computed.

Molecular structure, vibrational spectra, AIM, HOMO-LUMO, NBO, UV, first order hyperpolarizability, analysis of 3-thiophenecarboxylic acid monomer and dimer by Hartree-Fock and density functional theory.

PubMed

Issaoui, Noureddine; Ghalla, Houcine; Muthu, S; Flakus, H T; Oujia, Brahim

2015-02-05

In this work, the molecular structure, harmonic vibrational frequencies, UV, NBO and AIM of 3-thiophenecarboxilic acid (abbreviated as 3-TCA) monomer and dimer has been investigated. The FT-IR and FT-Raman spectra were recorded. The ground-state molecular geometry and vibrational frequencies have been calculated by using the Hartree-Fock (HF) and density functional theory (DFT)/B3LYP methods and 6-311++G(d,p) as a basis set. The fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with VEDA program. Comparison of the observed fundamental vibrational frequencies of 3-TCA with calculated results by HF and DFT methods indicates that B3LYP is better to HF method for molecular vibrational problems. The difference between the observed and scaled wavenumber values is very small. The theoretically predicted FT-IR and FT-Raman spectra of the title compound have been constructed. A study on the Mulliken atomic charges, the electronic properties were performed by time-dependent DFT (TD-DFT) approach, frontier molecular orbitals (HOMO-LUMO), molecular electrostatic potential (MEP) and thermodynamic properties have been performed. The electric dipole moment (μ) and the first hyperpolarizability (β) values of the investigated molecule have been also computed. Copyright © 2014 Elsevier B.V. All rights reserved.

Franck Condon shift assessment in 2D MoS2

NASA Astrophysics Data System (ADS)

Gupta, Sunny; Shirodkar, Sharmila N.; Kaplan, Daniel; Swaminathan, Venkataraman; Yakobson, Boris I.

2018-03-01

Optical spectroscopy (OS) techniques are often coupled with first-principles density functional theoretical (DFT) calculations for determining the precise influence of defects on the electronic and structural properties of two-dimensional (2D) transition metal dichalcogenides. Such calculations are carried out presuming there is little or no effect of vibrational transitions on the observed electronic spectrum. However, if the effect of change in vibrational energy (Franck Condon (FC) shift) associated with such a transition is large, it could possibly lead to a different origin for the observed peak. One such instance is the attribution of the 0.75 eV cathodoluminescence peak by Fabbri et al (2016 Nat. Commun. 7 13044) to an optical transition from an S vacancy level in the band gap, under the assumption that the FC shift is negligible. Here, by first principles constrained DFT calculations using hybrid HSE06 functional we show that this combined prediction of OS and DFT calculations is valid for 2D MoS2 since the FC shift associated with electronic transitions from a sulfur vacancy is indeed small ~28 meV. Based on our calculations we conclude that it is reasonable to make a direct connection between DFT calculations and optical spectroscopy techniques in this material, hence, establishing a one to one relation between defect related emission bands and electronic transitions from the defect levels.

Theoretical and spectroscopic studies of a tricyclic antidepressant, imipramine hydrochloride

NASA Astrophysics Data System (ADS)

Sagdinc, S. G.; Azkeskin, Caner; Eşme, A.

2018-06-01

Imipramine hydrochloride ([H-IMI]Cl), C19H24N2.HCl, is the prototypic tricyclic antidepressant (TCA) inhibitor of norepinephrine and serotonin neuronal reuptake. The molecular structure, molecular electrostatic potential (MEP), natural bond orbital (NBO) analysis, linear and non-linear optical (NLO) properties of [H-IMI]Cl have been investigated using the density functional theory (DFT) calculations with the B3LYP level at the 6‒311++G(d,p) basis set. The UV-Vis spectra for [H-IMI]Cl were experimentally studied in water and methanol. TD‒DFT calculations in water and methanol were employed to investigate the absorption wavelengths (λ), excitation energies (E), and oscillator strengths (f) for the UV-Vis analysis and the major contributions to the electronic transitions. From NBO analysis, the orbitals with the stabilization energy E(2) of 192.15 kcal/mol are π*(C5sbnd C18) as donor NBO and π*(C19sbnd C20) as acceptor NBO. The FT‒IR (4000‒400 cm-1) and FT‒Raman (3500-50 cm-1) spectra have been measured and analyzed. The assignment of bands observed vibrational spectra have been made by comparison of its calculated theoretical vibrational frequencies obtained using the DFT/B3LYP/6‒311++G(d,p) method. The detailed vibrational assignments were performed with the DFT calculation, and the potential energy distribution (PED) of [H-IMI]Cl was obtained by the Vibrational Energy Distribution Analysis 4 (VEDA4) program. The scaled frequencies resulted in good agreement with the observed spectral patterns.

DFT computations on: Crystal structure, vibrational studies and optical investigations of a luminescent self-assembled material

NASA Astrophysics Data System (ADS)

Kessentini, A.; Ben Ahmed, A.; Dammak, T.; Belhouchet, M.

2018-02-01

The current work undertakes the growth and the physicochemical properties of a novel green-yellow luminescence semi-organic material, the 3-picolylammonium bromide abbreviated (Pico-Br). In this paper, we report the X-ray diffraction measurements which show that the crystal lattice consists of distinct 3-picolylammonium cations and free bromide anions connected via Nsbnd H ⋯ Br and Nsbnd H ⋯ N hydrogen bonds leading to form a two dimensional frameworks. Molecular geometry compared with its optimized counterpart shows that the quantum chemical calculations carried out with density functional method (DFT) well produce the perceived structure by X-ray resolution of the studied material. To provide further insight into the spectroscopic properties, additional characterization of this material have been performed with Raman and infrared studies at room temperature. Theoretical computations have been computed using the (DFT) method at B3LYP/LanL2DZ level of theory implemented within Gaussian 03 program to study the vibrational spectra of the investigated molecule in the ground state. Optical absorption spectrum inspected by UV-visible absorption reveals the appearance of sharp optical gap of 280 nm (4.42 eV) as well as a strong green photoluminescence emission at 550 nm (2.25 eV) is detected on the photoluminescence (PL) spectrum at room temperature. Using the TD/DFT method, HOMO-LUMO energy gap and the Mulliken atomic charges were calculated in order to get an insight into the material. Good agreement between the theoretical results and the experimental ones was predicted.

Ab-initio and DFT methodologies for computing hyperpolarizabilities and susceptibilities of highly conjugated organic compounds for nonlinear optical applications

NASA Astrophysics Data System (ADS)

Karakas, A.; Karakaya, M.; Ceylan, Y.; El Kouari, Y.; Taboukhat, S.; Boughaleb, Y.; Sofiani, Z.

2016-06-01

In this talk, after a short introduction on the methodologies used for computing dipole polarizability (α), second and third-order hyperpolarizability and susceptibility; the results of theoretical studies performed on density functional theory (DFT) and ab-initio quantum mechanical calculations of nonlinear optical (NLO) properties for a few selected organic compounds and polymers will be explained. The electric dipole moments (μ) and dispersion-free first hyperpolarizabilities (β) for a family of azo-azulenes and a styrylquinolinium dye have been determined by DFT at B3LYP level. To reveal the frequency-dependent NLO behavior, the dynamic α, second hyperpolarizabilities (γ), second (χ(2)) and third-order (χ(3)) susceptibilites have been evaluated using time-dependent HartreeFock (TDHF) procedure. To provide an insight into the third-order NLO phenomena of a series of pyrrolo-tetrathiafulvalene-based molecules and pushpull azobenzene polymers, two-photon absorption (TPA) characterizations have been also investigated by means of TDHF. All computed results of the examined compounds are compared with their previous experimental findings and the measured data for similar structures in the literature. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by configuration interaction (CI) method. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO-LUMO band gaps have been revealed by DFT at B3LYP level for azo-azulenes, styrylquinolinium dye, push-pull azobenzene polymers and by parametrization method 6 (PM6) for pyrrolo-tetrathiafulvalene-based molecules.

Many-Body Perturbation Theory (MBPT) and Time-Dependent Density-Functional Theory (TD-DFT): MBPT Insights About What Is Missing In, and Corrections To, the TD-DFT Adiabatic Approximation.

PubMed

Casida, Mark E; Huix-Rotllant, Miquel

2016-01-01

In their famous paper, Kohn and Sham formulated a formally exact density-functional theory (DFT) for the ground-state energy and density of a system of N interacting electrons, albeit limited at the time by certain troubling representability questions. As no practical exact form of the exchange-correlation (xc) energy functional was known, the xc-functional had to be approximated, ideally by a local or semilocal functional. Nowadays, however, the realization that Nature is not always so nearsighted has driven us up Perdew's Jacob's ladder to find increasingly nonlocal density/wavefunction hybrid functionals. Time-dependent (TD-) DFT is a younger development which allows DFT concepts to be used to describe the temporal evolution of the density in the presence of a perturbing field. Linear response (LR) theory then allows spectra and other information about excited states to be extracted from TD-DFT. Once again the exact TD-DFT xc-functional must be approximated in practical calculations and this has historically been done using the TD-DFT adiabatic approximation (AA) which is to TD-DFT very similar to what the local density approximation (LDA) is to conventional ground-state DFT. Although some of the recent advances in TD-DFT focus on what can be done within the AA, others explore ways around the AA. After giving an overview of DFT, TD-DFT, and LR-TD-DFT, this chapter focuses on many-body corrections to LR-TD-DFT as one way to build hybrid density-functional/wavefunction methodology for incorporating aspects of nonlocality in time not present in the AA.

FTIR, FT-RAMAN, NMR, spectra, normal co-ordinate analysis, NBO, NLO and DFT calculation of N,N-diethyl-4-methylpiperazine-1-carboxamide molecule

NASA Astrophysics Data System (ADS)

Muthu, S.; Elamurugu Porchelvi, E.

2013-11-01

The Fourier Transform Infrared (FT-IR) and FT-Raman of N,N-diethyl-4-methylpiperazine-1-carboxamide (NND4MC) have been recorded and analyzed. The structure of the compound was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(d,p) and 6-311G(d,p) basis sets. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The theoretically predicted FT-IR and FT-Raman spectra of the title molecule have been constructed. The detailed interpretation of the vibrational spectra has been carried out with aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the σ* and π* antibonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. The electronic dipole moment (μD) and the first hyperpolarizability (βtot) values of the investigated molecule were computed using Density Functional Theory (DFT/B3LYP) with 6-31G(d,p) and 6-311G(d,p) basis sets. The calculated results also show that the NND4MC molecule may have microscopy nonlinear optical (NLO) behavior with non zero values. Mulliken atomic charges of NND4MC were calculated. The 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. The UV-Vis spectrum of the compound was recorded. The theoretical electronic absorption spectra have been calculated by using CIS, TD-DFT methods. A study on the electronic properties, such as HOMO and LUMO energies, molecular electrostatic potential (MEP) were also performed.

Molecular structure, NMR, UV-Visible, vibrational spectroscopic and HOMO, LUMO analysis of (E)-1-(2, 6-bis (4-methoxyphenyl)-3, 3-dimethylpiperidine-4-ylidene)-2-(3-(3, 5-dimethyl-1H-pyrazol-1-yl) pyrazin-2-yl) hydrazine by DFT method

NASA Astrophysics Data System (ADS)

Alphonsa, A. Therasa; Loganathan, C.; Anand, S. Athavan Alias; Kabilan, S.

2016-02-01

We have synthesized (E)-1-(2, 6-bis (4-methoxyphenyl)-3, 3-dimethylpiperidine-4-ylidene)-2-(3-(3, 5-dimethyl-1H-pyrazol-1-yl) pyrazin-2-yl) hydrazine (PM6). It was characterized using FT-IR, FT-Raman, 1H NMR, 13C NMR techniques. To interpret the experimental data, ab initio computations of the vibrational frequencies were carried out using the Gaussian 09 program followed by the full optimizations done using Density Functional Theory (DFT) at B3LYP/6-311 G(d,p) level. The combined use of experiments and computations allowed a firm assignment of the majority of observed bands for the compound. The calculated stretching frequencies have been found to be in good agreement with the experimental frequencies. The electronic and charge transfer properties have been explained on the basis of highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs) and density of states (DOS). The absorption spectra have been computed by using time dependent density functional theory (TD-DFT). 1H and 13C NMR spectra were recorded and 1H and 13C NMR chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. From the optimized geometry of the molecule, molecular electrostatic potential (MEP) distribution, frontier molecular orbitals (FMOs) of the title compound have been calculated in the ground state theoretically. The theoretical results showed good agreement with the experimental values.

Experimental and theoretical spectroscopic studies of anticancer drug rosmarinic acid using HF and density functional theory.

PubMed

Mariappan, G; Sundaraganesan, N; Manoharan, S

2012-11-01

In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of anticancer drug of rosmarinic acid. The optimized molecular structure, atomic charges, vibrational frequencies, natural bond orbital analysis and ultraviolet-visible spectral interpretation of rosmarinic acid have been studied by performing HF and DFT/B3LYP/6-31G(d,p) level of theory. The FT-IR (solid and solution phase), FT-Raman (solid phase) spectra were recorded in the region 4000-400 and 3500-50 cm(-1), respectively. The UV-Visible absorption spectra of the compound that dissolved in ethanol were recorded in the range of 200-800 nm. The scaled wavenumbers are compared with the experimental values. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The formation of hydrogen bond was investigated in terms of the charge density by the NBO calculations. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands were carried out. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations. Copyright © 2012 Elsevier B.V. All rights reserved.

A systematic theoretical study of the electronic structures of porphyrin dimers: DFT and TD-DFT calculations on diporphyrins linked by ethane, ethene, ethyne, imine, and azo bridges.

PubMed

Rintoul, Llew; Harper, Shannon R; Arnold, Dennis P

2013-11-21

Theoretical calculations of the geometries, electronic structures and electronic absorption spectra of a series of covalently-linked porphyrin dimers are reported. The diporphyrins comprise 5,10,15-triphenylporphyrinatozinc(II) (ZnTriPP) units linked through the meso carbons by two-atom bridges, namely 1,2-ethanediyl (1), trans-1,2-ethenediyl (2), ethynediyl (3), 1,2-iminomethenediyl (4), and transdiazenediyl (5). The structures were optimised in toluene solvent by Density Functional Theory (DFT), using the integral equation formalism variant of the polarizable continuum model. The calculations were performed using the B3LYP functional and the 6-31G(d,p) basis set. The complete molecules were modelled, with no substitution of smaller groups on the periphery. In parallel, the compounds 2–5 were prepared by known or novel synthetic routes, to enable comparisons of experimental electronic absorption spectra with those calculated using time dependent-DFT at the same level of theory. As the ethane dimer 1 is not yet synthetically accessible, the model monomer meso-2-phenylethylZnTriPP was used for comparisons with the theoretical predictions. The results form a self-consistent set, enabling for the first time legitimate comparisons of the electronic structures of the series, especially regarding the degree to which the porphyrin p-systems interact by conjugation across the bridges. The theoretical calculations of the electronic transitions match the observed spectra in toluene to a remarkable degree, especially with respect to the peak maximum of the Q band, which represents to a large degree the energy of the HOMO–LUMO transition. The imine 4 is intrinsically polar due to the asymmetric bridge, and the HOMO is located almost exclusively on the ZnTriPP unit attached to the nitrogen of the imine, and the LUMO on the C-attached ring. Thus the Q-band transition is mapped as a comprehensive charge-transfer from the former ring to the latter. This may have consequences for the non-linear optical properties of the system. The azoporphyrin 5 exhibits the largest splittings between the interacting MOs via the conjugated bridge, vindicating a prediction by Anderson and co-workers in 2002, and confirmed experimentally by our synthesis of 5. The collected results also indicate that this level of theory is more thanadequate as a model with which to handle these large delocalised molecules.

A combined experimental and DFT study of a novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine

NASA Astrophysics Data System (ADS)

Vijaya, P.; Sankaran, K. R.

2015-03-01

A novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine (UA) was prepared and characterized by IR, 1H and 13C NMR spectral studies. A 2D - potential energy scan (PES) of p-isobutylacetophenone (IBAP) was the portal to the conformational analysis of UA by density functional theory (DFT) methods using 6-31G(d,p) basis set by Gaussian 03 program. The theoretical IR frequencies were found to be in good agreement with the experimental values. The IR frequencies of UA were analyzed by means of Potential energy Distribution (PED %) calculation using Vibrational Energy Distribution Analysis (VEDA 4) program. The experimental NMR chemical shift values of UA were compared with the theoretical values obtained by DFT method. Nonlinear optical behavior of the unsymmetrical azine is also examined by the theoretically predicted values of dipole moment (μ), polarizability (α0) and first hyperpolarizability (βtot). Stability of the UA molecule has been analyzed using NBO analysis. The electrochemistry of UA studied experimentally by cyclic voltammetry is complemented by the computational analysis of the anionic form of the molecule UA. The determination of various global and local reactivity descriptors in the context of chemical reactivity is also performed and the electrophilicity at the vital atomic sites in UA is revealed. Bader's Atoms in molecules (AIM) theory of UA indicated the presence of intramolecular hydrogen bonding in the molecule. The molecular electrostatic potential (MEP) and HOMO-LUMO orbital analysis are also performed for the molecule UA.

A combined experimental and DFT study of a novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine.

PubMed

Vijaya, P; Sankaran, K R

2015-03-05

A novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine (UA) was prepared and characterized by IR, (1)H and (13)C NMR spectral studies. A 2D - potential energy scan (PES) of p-isobutylacetophenone (IBAP) was the portal to the conformational analysis of UA by density functional theory (DFT) methods using 6-31G(d,p) basis set by Gaussian 03 program. The theoretical IR frequencies were found to be in good agreement with the experimental values. The IR frequencies of UA were analyzed by means of Potential energy Distribution (PED %) calculation using Vibrational Energy Distribution Analysis (VEDA 4) program. The experimental NMR chemical shift values of UA were compared with the theoretical values obtained by DFT method. Nonlinear optical behavior of the unsymmetrical azine is also examined by the theoretically predicted values of dipole moment (μ), polarizability (α0) and first hyperpolarizability (βtot). Stability of the UA molecule has been analyzed using NBO analysis. The electrochemistry of UA studied experimentally by cyclic voltammetry is complemented by the computational analysis of the anionic form of the molecule UA. The determination of various global and local reactivity descriptors in the context of chemical reactivity is also performed and the electrophilicity at the vital atomic sites in UA is revealed. Bader's Atoms in molecules (AIM) theory of UA indicated the presence of intramolecular hydrogen bonding in the molecule. The molecular electrostatic potential (MEP) and HOMO-LUMO orbital analysis are also performed for the molecule UA. Copyright © 2014 Elsevier B.V. All rights reserved.

Theoretical investigation of structural, electronic and optical properties of MgxBa1-xS, MgxBa1-xSe and MgxBa1-xTe ternary alloys using DFT based FP-LAPW approach

NASA Astrophysics Data System (ADS)

Bhattacharjee, Rahul; Chattopadhyaya, Surya

2017-11-01

Density functional theory (DFT) based full-potential linearized augmented plane wave (FP-LAPW) methodology has been employed to investigate theoretically the structural, electronic and optical properties of MgxBa1-xS, MgxBa1-xSe and MgxBa1-xTe ternary alloys for 0 ≤ x ≤ 1 in their rock-salt (B1) crystallographic phase. The exchange-correlation potentials for the structural properties have been computed using the Wu-Cohen generalized-gradient approximation (WC-GGA) scheme, while those for the electronic and optical properties have been computed using both the WC-GGA and the recently developed Tran-Blaha modified Becke-Johnson (TB-mBJ) schemes. The thermodynamic stability of all the ternary alloys have been investigated by calculating their respective enthalpy of formation. The atomic and orbital origin of different electronic states in the band structure of the compounds have been identified from the respective density of states (DOS). Using the approach of Zunger and co-workers, the microscopic origin of band gap bowing has been discussed in term of volume deformation, charge exchange and structural relaxation. Bonding characteristics among the constituent atoms of each of the specimens have been discussed from their charge density contour plots. Optical properties of the binary compounds and ternary alloys have been investigated theoretically in terms of their respective dielectric function, refractive index, normal incidence reflectivity and optical conductivity. Several calculated results have been compared with available experimental and other theoretical data.

Spectral and structural studies of the anti-cancer drug Flutamide by density functional theoretical method.

PubMed

Mariappan, G; Sundaraganesan, N

2014-01-03

A comprehensive screening of the more recent DFT theoretical approach to structural analysis is presented in this section of theoretical structural analysis. The chemical name of 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide is usually called as Flutamide (In the present study it is abbreviated as FLT) and is an important and efficacious drug in the treatment of anti-cancer resistant. The molecular geometry, vibrational spectra, electronic and NMR spectral interpretation of Flutamide have been studied with the aid of density functional theory method (DFT). The vibrational assignments of the normal modes were performed on the basis of the PED calculations using the VEDA 4 program. Comparison of computational results with X-ray diffraction results of Flutamide allowed the evaluation of structure predictions and confirmed B3LYP/6-31G(d,p) as accurate for structure determination. Application of scaling factors for IR and Raman frequency predictions showed good agreement with experimental values. This is supported the assignment of the major contributors of the vibration modes of the title compound. Stability of the molecule arising from hyperconjugative interactions leading to its bioactivity, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. NMR chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. The comparison of measured FTIR, FT-Raman, and UV-Visible data to calculated values allowed assignment of major spectral features of the title molecule. Besides, Frontier molecular orbital analyze was also investigated using theoretical calculations. Copyright © 2013 Elsevier B.V. All rights reserved.

DFT-BASED AB INITIO STUDY OF THE ELECTRONIC AND OPTICAL PROPERTIES OF CESIUM BASED FLUORO-PEROVSKITE CsMF3 (M = Ca AND Sr)

NASA Astrophysics Data System (ADS)

Harmel, M.; Khachai, H.; Ameri, M.; Khenata, R.; Baki, N.; Haddou, A.; Abbar, B.; UǦUR, Ş.; Omran, S. Bin; Soyalp, F.

2012-12-01

Density functional theory (DFT) is performed to study the structural, electronic and optical properties of cubic fluoroperovskite AMF3 (A = Cs; M = Ca and Sr) compounds. The calculations are based on the total-energy calculations within the full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential is treated by local density approximation (LDA) and generalized gradient approximation (GGA). The structural properties, including lattice constants, bulk modulus and their pressure derivatives are in very good agreement with the available experimental and theoretical data. The calculations of the electronic band structure, density of states and charge density reveal that compounds are both ionic insulators. The optical properties (namely: the real and the imaginary parts of the dielectric function ɛ(ω), the refractive index n(ω) and the extinction coefficient k(ω)) were calculated for radiation up to 40.0 eV.

Pair potentials for warm dense matter and their application to x-ray Thomson scattering in aluminum and beryllium.

PubMed

Harbour, L; Dharma-Wardana, M W C; Klug, D D; Lewis, L J

2016-11-01

Ultrafast laser experiments yield increasingly reliable data on warm dense matter, but their interpretation requires theoretical models. We employ an efficient density functional neutral-pseudoatom hypernetted-chain (NPA-HNC) model with accuracy comparable to ab initio simulations and which provides first-principles pseudopotentials and pair potentials for warm-dense matter. It avoids the use of (i) ad hoc core-repulsion models and (ii) "Yukawa screening" and (iii) need not assume ion-electron thermal equilibrium. Computations of the x-ray Thomson scattering (XRTS) spectra of aluminum and beryllium are compared with recent experiments and with density-functional-theory molecular-dynamics (DFT-MD) simulations. The NPA-HNC structure factors, compressibilities, phonons, and conductivities agree closely with DFT-MD results, while Yukawa screening gives misleading results. The analysis of the XRTS data for two of the experiments, using two-temperature quasi-equilibrium models, is supported by calculations of their temperature relaxation times.

Si Nanoribbons on Ag(110) Studied by Grazing-Incidence X-Ray Diffraction, Scanning Tunneling Microscopy, and Density-Functional Theory: Evidence of a Pentamer Chain Structure.

PubMed

Prévot, Geoffroy; Hogan, Conor; Leoni, Thomas; Bernard, Romain; Moyen, Eric; Masson, Laurence

2016-12-30

We report a combined grazing incidence x-ray diffraction (GIXD), scanning tunneling microscopy (STM), and density-functional theory (DFT) study which clearly elucidates the atomic structure of the Si nanoribbons grown on the missing-row reconstructed Ag(110) surface. Our study allows us to discriminate between the theoretical models published in the literature, including the most stable atomic configurations and those based on a missing-row reconstructed Ag(110) surface. GIXD measurements unambiguously validate the pentamer model grown on the reconstructed surface, obtained from DFT. This pentamer atomistic model accurately matches the high-resolution STM images of the Si nanoribbons adsorbed on Ag(110). Our study closes the long-debated atomic structure of the Si nanoribbons grown on Ag(110) and definitively excludes a honeycomb structure similar to that of freestanding silicene.

INFRARED SPECTRUM OF POTASSIUM-CATIONIZED TRIETHYLPHOSPHATE GENERATED USING TANDEM MASS SPECTROMETRY AND INFRARED MULTIPLE PHOTON DISSOCIATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gary S. Groenewold; Christopher M. Leavitt; Ryan P. Dain

2009-09-01

Tandem mass spectrometry and wavelength selective infrared photodissociation was used to generate an infrared spectrum of gas-phase triethylphosphate cationized by attachment of K+. Prominent absorptions were observed in the region of 900 to 1300 cm-1 that are characteristic of phosphate P=O and P-O-R stretches. The relative positions and intensities of the IR absorptions were reproduced well by density functional theory (DFT) calculations performed using the B3LYP functional and the 6-31+g(d), 6-311+g(d,p) and 6-311++G(3df,2pd) basis sets. Because of good correspondence between experiment and theory for the cation, DFT was then used to generate a theoretical spectrum for neutral triethylphosphate, which inmore » turn accurately reproduces the IR spectrum of the neat liquid when solvent effects are included in the calculations.« less

Molecular conformational analysis, vibrational spectra and normal coordinate analysis of trans-1,2-bis(3,5-dimethoxy phenyl)-ethene based on density functional theory calculations.

PubMed

Joseph, Lynnette; Sajan, D; Chaitanya, K; Isac, Jayakumary

2014-03-25

The conformational behavior and structural stability of trans-1,2-bis(3,5-dimethoxy phenyl)-ethene (TDBE) were investigated by using density functional theory (DFT) method with the B3LYP/6-311++G(d,p) basis set combination. The vibrational wavenumbers of TDBE were computed at DFT level and complete vibrational assignments were made on the basis of normal coordinate analysis calculations (NCA). The DFT force field transformed to natural internal coordinates was corrected by a well-established set of scale factors that were found to be transferable to the title compound. The infrared and Raman spectra were also predicted from the calculated intensities. The observed Fourier transform infrared (FTIR) and Fourier transform (FT) Raman vibrational wavenumbers were analyzed and compared with the theoretically predicted vibrational spectra. Comparison of the simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surfaces (ESP). Copyright © 2013 Elsevier B.V. All rights reserved.

Investigation of the Fe{sup 3+} centers in perovskite KMgF{sub 3} through a combination of ab initio (density functional theory) and semi-empirical (superposition model) calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emül, Y.; Department of Software Engineering, Cumhuriyet University, 58140 Sivas; Erbahar, D.

2015-08-14

Analyses of the local crystal and electronic structure in the vicinity of Fe{sup 3+} centers in perovskite KMgF{sub 3} crystal have been carried out in a comprehensive manner. A combination of density functional theory (DFT) and a semi-empirical superposition model (SPM) is used for a complete analysis of all Fe{sup 3+} centers in this study for the first time. Some quantitative information has been derived from the DFT calculations on both the electronic structure and the local geometry around Fe{sup 3+} centers. All of the trigonal (K-vacancy case, K-Li substitution case, and normal trigonal Fe{sup 3+} center case), FeF{sub 5}Omore » cluster, and tetragonal (Mg-vacancy and Mg-Li substitution cases) centers have been taken into account based on the previously suggested experimental and theoretical inferences. The collaboration between the experimental data and the results of both DFT and SPM calculations provides us to understand most probable structural model for Fe{sup 3+} centers in KMgF{sub 3}.« less

High-temperature high-pressure properties of silica from Quantum Monte Carlo and Density Functional Perturbation Theory

NASA Astrophysics Data System (ADS)

Cohen, R. E.; Driver, K.; Wu, Z.; Militzer, B.; Rios, P. L.; Towler, M.; Needs, R.

2009-03-01

We have used diffusion quantum Monte Carlo (DMC) with the CASINO code with thermal free energies from phonons computed using density functional perturbation theory (DFPT) with the ABINIT code to obtain phase transition curves and thermal equations of state of silica phases under pressure. We obtain excellent agreement with experiments for the metastable phase transition from quartz to stishovite. The local density approximation (LDA) incorrectly gives stishovite as the ground state. The generalized gradient approximation (GGA) correctly gives quartz as the ground state, but does worse than LDA for the equations of state. DMC, variational quantum Monte Carlo (VMC), and DFT all give good results for the ferroelastic transition of stishovite to the CaCl2 structure, and LDA or the WC exchange correlation potentials give good results within a given silica phase. The δV and δH from the CaCl2 structure to α-PbO2 is small, giving uncertainly in the theoretical transition pressure. It is interesting that DFT has trouble with silica transitions, although the electronic structures of silica are insulating, simple closed-shell with ionic/covalent bonding. It seems like the errors in DFT are from not precisely giving the ion sizes.

Theoretical insight of adsorption thermodynamics of multifunctional molecules on metal surfaces

NASA Astrophysics Data System (ADS)

Loffreda, David

2006-05-01

Adsorption thermodynamics based on density functional theory (DFT) calculations are exposed for the interaction of several multifunctional molecules with Pt and Au(1 1 0)-(1 × 2) surfaces. The Gibbs free adsorption energy explicitly depends on the adsorption internal energy, which is derived from DFT adsorption energy, and the vibrational entropy change during the chemisorption process. Zero-point energy (ZPE) corrections have been systematically applied to the adsorption energy. Moreover the vibrational entropy change has been computed on the basis of DFT harmonic frequencies (gas and adsorbed phases, clean surfaces), which have been extended to all the adsorbate vibrations and the metallic surface phonons. The phase diagrams plotted in realistic conditions of temperature (from 100 to 400 K) and pressure (0.15 atm) show that the ZPE corrected adsorption energy is the main contribution. When strong chemisorption is considered on the Pt surface, the multifunctional molecules are adsorbed on the surface in the considered temperature range. In contrast for weak chemisorption on the Au surface, the thermodynamic results should be held cautiously. The systematic errors of the model (choice of the functional, configurational entropy and vibrational entropy) make difficult the prediction of the adsorption-desorption phase boundaries.

Crystal growth, spectroscopic, DFT computational and third harmonic generation studies of nicotinic acid

NASA Astrophysics Data System (ADS)

Thaya Kumari, C. Rathika; Nageshwari, M.; Raman, R. Ganapathi; Caroline, M. Lydia

2018-07-01

An organic centrosymmetric nicotinic acid (NA) single crystal has been grown employing slow evaporation method in water. NA crystallizes in monoclinic system with centric space group P21/C. The experimental and theoretical investigation includes vibrational spectra based on Hartree - Fock (HF) and density functional theory (DFT) has been applied using different function at B3LYP level of theory using 6-311G++(d,p) basis set. The optical transparency of the title molecule was examined by TD- DFT analysis and for comparison basis experimental UV-Vis spectrum was recorded. The interaction of charge within the molecule was analyzed and the HOMO - LUMO energy gap was evaluated. The value of dipole moment, Mulliken charge and molecular electrostatic potential were estimated at the same level of theory. Also the first order hyper polarizability for NA was calculated. The dielectric behavior of the grown crystal was determined for few selected temperatures. The third order nonlinear response of NA has been examined using Z-scan technique and nonlinear susceptibility (χ3), nonlinear refraction (n2) and nonlinear absorption coefficient (β) has been calculated. The current results clearly indicate that the title compound is an excellent applicant in the domain of opto - electronic applications.

Neural network consistent empirical physical formula construction for density functional theory based nonlinear vibrational absorbance and intensity of 6-choloronicotinic acid molecule

NASA Astrophysics Data System (ADS)

Yildiz, Nihat; Karabacak, Mehmet; Kurt, Mustafa; Akkoyun, Serkan

2012-05-01

Being directly related to the electric charge distributions in a molecule, the vibrational spectra intensities are both experimentally and theoretically important physical quantities. However, these intensities are inherently highly nonlinear and of complex pattern. Therefore, in particular for unknown detailed spatial molecular structures, it is difficult to make ab initio intensity calculations to compare with new experimental data. In this respect, we very recently initiated entirely novel layered feedforward neural network (LFNN) approach to construct empirical physical formulas (EPFs) for density functional theory (DFT) vibrational spectra of some molecules. In this paper, as a new and far improved contribution to our novel molecular vibrational spectra LFNN-EPF approach, we constructed LFFN-EPFs for absorbances and intensities of 6-choloronicotinic acid (6-CNA) molecule. The 6-CNA data, borrowed from our previous study, was entirely different and much larger than the vibrational intensity data of our formerly used LFNN-EPF molecules. In line with our another previous work which theoretically proved the LFNN relevance to EPFs, although the 6-CNA DFT absorbance and intensity were inherently highly nonlinear and sharply fluctuating in character, still the optimally constructed train set LFFN-EPFs very successfully fitted the absorbances and intensities. Moreover, test set (i.e. yet-to-be measured experimental data) LFNN-EPFs consistently and successfully predicted the absorbance and intensity data. This simply means that the physical law embedded in the 6-CNA vibrational data was successfully extracted by the LFNN-EPFs. In conclusion, these vibrational LFNN-EPFs are of explicit form. Therefore, by various suitable operations of mathematical analysis, they can be used to estimate the electronic charge distributions of the unknown molecule of the significant complexity. Additionally, these estimations can be combined with those of theoretical DFT atomic polar tensor calculations to contribute to the identification of the molecule.

The CC/DFT Route towards Accurate Structures and Spectroscopic Features for Observed and Elusive Conformers of Flexible Molecules: Pyruvic Acid as Case Study

PubMed Central

Barone, Vincenzo; Biczysko, Malgorzata; Bloino, Julien; Cimino, Paola; Penocchio, Emanuele; Puzzarini, Cristina

2018-01-01

The structures, relative stabilities as well as the rotational and vibrational spectra of the three low-energy conformers of Pyruvic acid (PA) have been characterized using a state-of-the-art quantum-mechanical approach designed for flexible molecules. By making use of the available experimental rotational constants for several isotopologues of the most stable PA conformer, Tc-PA, the semi-experimental equilibrium structure has been derived. The latter provides a reference for the pure theoretical determination of the equilibrium geometries for all conformers, thus confirming for these structures an accuracy of 0.001 Å and 0.1 deg. for bond lengths and angles, respectively. Highly accurate relative energies of all conformers (Tc-, Tt- and Ct-PA) and of the transition states connecting them are provided along with the thermodynamic properties at low and high temperatures, thus leading to conformational enthalpies accurate to 1 kJ mol−1. Concerning microwave spectroscopy, rotational constants accurate to about 20 MHz are provided for the Tt- and Ct-PA conformers, together with the computed centrifugal-distortion constants and dipole moments required to simulate their rotational spectra. For Ct-PA, vibrational frequencies in the mid-infrared region accurate to 10 cm−1 are reported along with theoretical estimates for the transitions in the near-infrared range, and the corresponding infrared spectrum including fundamental transitions, overtones and combination bands has been simulated. In addition to the new data described above, theoretical results for the Tc- and Tt-PA conformers are compared with all available experimental data to further confirm the accuracy of the hybrid coupled-cluster/density functional theory (CC/DFT) protocol applied in the present study. Finally, we discuss in detail the accuracy of computational models fully based on double-hybrid DFT functionals (mainly at the B2PLYP/aug-cc-pVTZ level) that avoid the use of very expensive CC calculations. PMID:26575928

Neural network consistent empirical physical formula construction for density functional theory based nonlinear vibrational absorbance and intensity of 6-choloronicotinic acid molecule.

PubMed

Yildiz, Nihat; Karabacak, Mehmet; Kurt, Mustafa; Akkoyun, Serkan

2012-05-01

Being directly related to the electric charge distributions in a molecule, the vibrational spectra intensities are both experimentally and theoretically important physical quantities. However, these intensities are inherently highly nonlinear and of complex pattern. Therefore, in particular for unknown detailed spatial molecular structures, it is difficult to make ab initio intensity calculations to compare with new experimental data. In this respect, we very recently initiated entirely novel layered feedforward neural network (LFNN) approach to construct empirical physical formulas (EPFs) for density functional theory (DFT) vibrational spectra of some molecules. In this paper, as a new and far improved contribution to our novel molecular vibrational spectra LFNN-EPF approach, we constructed LFFN-EPFs for absorbances and intensities of 6-choloronicotinic acid (6-CNA) molecule. The 6-CNA data, borrowed from our previous study, was entirely different and much larger than the vibrational intensity data of our formerly used LFNN-EPF molecules. In line with our another previous work which theoretically proved the LFNN relevance to EPFs, although the 6-CNA DFT absorbance and intensity were inherently highly nonlinear and sharply fluctuating in character, still the optimally constructed train set LFFN-EPFs very successfully fitted the absorbances and intensities. Moreover, test set (i.e. yet-to-be measured experimental data) LFNN-EPFs consistently and successfully predicted the absorbance and intensity data. This simply means that the physical law embedded in the 6-CNA vibrational data was successfully extracted by the LFNN-EPFs. In conclusion, these vibrational LFNN-EPFs are of explicit form. Therefore, by various suitable operations of mathematical analysis, they can be used to estimate the electronic charge distributions of the unknown molecule of the significant complexity. Additionally, these estimations can be combined with those of theoretical DFT atomic polar tensor calculations to contribute to the identification of the molecule. Copyright © 2012 Elsevier B.V. All rights reserved.

Application of spectroscopic methods (FT-IR, Raman, ECD and NMR) in studies of identification and optical purity of radezolid

NASA Astrophysics Data System (ADS)

Michalska, Katarzyna; Gruba, Ewa; Mizera, Mikołaj; Lewandowska, Kornelia; Bednarek, Elżbieta; Bocian, Wojciech; Cielecka-Piontek, Judyta

2017-08-01

In the presented study, N-{[(5S)-3-(2-fluoro-4‧-{[(1H-1,2,3-triazol-5-ylmethyl)amino]methyl}biphenyl-4-yl)-2-oxo-1,3-oxazolidin-5-yl]methyl}acetamide (radezolid) was synthesized and characterized using FT-IR, Raman, ECD and NMR. The aim of this work was to assess the possibility of applying classical spectral methods such as FT-IR, Raman, ECD and NMR spectroscopy for studies on the identification and optical purity of radezolid. The experimental interpretation of FT-IR and Raman spectra of radezolid was conducted in combination with theoretical studies. Density functional theory (DFT) with the B3LYP hybrid functional was used for obtaining radezolid spectra. Full identification was carried out by COSY, 1H {13C} HSQC and 1H {13C} HMBC experiments. The experimental NMR chemical shifts and spin-spin coupling constants were compared with theoretical calculations using the DFT method and B3LYP functional employing the 6-311 ++G(d,p) basis set and the solvent polarizable continuum model (PCM). The experimental ECD spectra of synthesized radezolid were compared with experimental spectra of the reference standard of radezolid. Theoretical calculations enabled us to conduct HOMO and LUMO analysis and molecular electrostatic potential maps were used to determine the active sites of microbiologically active form of radezolid enantiomer. The relationship between results of ab initio calculations and knowledge about chemical-biological properties of S-radezolid and other oxazolidinone derivatives are also discussed.

Electrocatalysis of borohydride oxidation: a review of density functional theory approach combined with experimental validation.

PubMed

Escaño, Mary Clare Sison; Arevalo, Ryan Lacdao; Gyenge, Elod; Kasai, Hideaki

2014-09-03

The electrocatalysis of borohydride oxidation is a complex, up-to-eight-electron transfer process, which is essential for development of efficient direct borohydride fuel cells. Here we review the progress achieved by density functional theory (DFT) calculations in explaining the adsorption of BH4(-) on various catalyst surfaces, with implications for electrocatalyst screening and selection. Wherever possible, we correlate the theoretical predictions with experimental findings, in order to validate the proposed models and to identify potential directions for further advancements.

Electrocatalysis of borohydride oxidation: a review of density functional theory approach combined with experimental validation

NASA Astrophysics Data System (ADS)

Sison Escaño, Mary Clare; Lacdao Arevalo, Ryan; Gyenge, Elod; Kasai, Hideaki

2014-09-01

The electrocatalysis of borohydride oxidation is a complex, up-to-eight-electron transfer process, which is essential for development of efficient direct borohydride fuel cells. Here we review the progress achieved by density functional theory (DFT) calculations in explaining the adsorption of BH4- on various catalyst surfaces, with implications for electrocatalyst screening and selection. Wherever possible, we correlate the theoretical predictions with experimental findings, in order to validate the proposed models and to identify potential directions for further advancements.

Structural, optoelectronic, infrared and Raman spectra of orthorhombic SrSnO{sub 3} from DFT calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moreira, E.; Henriques, J.M.; Azevedo, D.L.

2011-04-15

Orthorhombic SrSnO{sub 3} was investigated using density functional theory (DFT) considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The electronic band structure, density of states, complex dielectric function, optical absorption, and the infrared and Raman spectra were computed. Calculated lattice parameters are close to the experimental measurements, and an indirect band gap E(S{yields}{Gamma})=1.97eV (2.27 eV) was obtained within the GGA (LDA) level of calculation. Effective masses for holes and electrons were estimated, being very anisotropic in comparison with similar results for orthorhombic CaSnO{sub 3}. The complex dielectric function and the optical absorption of SrSnO{sub 3}more » were shown to be sensitive to the plane of polarization of the incident light. The infrared spectrum between 100 and 600 cm{sup -1} was obtained, with its main peaks being assigned, and a nice agreement between experimental and theoretical peaks of the Raman spectrum of orthorhombic SrSnO{sub 3} was achieved. -- Graphical abstract: Orthorhombic SrSnO{sub 3}: a view of the unit cell (left) and plots showing the calculated and experimental Raman spectra (right). Display Omitted Research highlights: {yields} We have performed DFT calculations on orthorhombic SrSnO{sub 3} crystals, obtaining their structural, electronical and optical properties. {yields} An indirect band gap was obtained, and anisotropic effective masses were found for both electrons and holes. {yields} The complex dielectric function and the optical absorption of SrSnO{sub 3} were shown to be very sensitive to the plane of polarization of the incident light. {yields} The infrared spectrum between 100 and 600 cm{sup -1} was obtained, with its main peaks being assigned, and a nice agreement between experimental and theoretical peaks of the Raman spectrum was achieved.« less

The spectroscopic (FT-IR, UV-vis), Fukui function, NLO, NBO, NPA and tautomerism effect analysis of (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile.

PubMed

Demircioğlu, Zeynep; Kaştaş, Çiğdem Albayrak; Büyükgüngör, Orhan

2015-03-15

A new o-hydroxy Schiff base, (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile was isolated and investigated by experimental and theoretical methodologies. The solid state molecular structure was determined by X-ray diffraction method. The vibrational spectral analysis was carried out by using FT-IR spectroscopy in the range of 4000-400cm(-)(1). Theoretical calculations were performed by density functional theory (DFT) method using 6-31G(d,p) basis set. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The UV-vis spectrum of the compound was recorded in the region 200-800 nm in several solvents and electronic properties such as excitation energies, and wavelengths were calculated by TD-DFT/B3LYP method. The most prominent transitions were corresponds to π→π∗. Hybrid density functional theory (DFT) was used to investigate the enol-imine and keto-amine tautomers of titled compound. The titled compound showed the preference of enol form, as supported by X-ray and spectroscopic analysis results. The geometric and molecular properties were compaired for both enol-imine and keto-amine forms. Additionally, geometry optimizations in solvent media were performed with the same level of theory by the integral equation formalism polarizable continuum (IEF-PCM). Stability of the molecule arises from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed using natural bond orbital (NBO) analysis. Mulliken population method and natural population analysis (NPA) have been studied. Also, condensed Fukui function and relative nucleophilicity indices calculated from charges obtained with orbital charge calculation methods (NPA). Molecular electrostatic potential (MEP) and non linear optical (NLO) properties are also examined. Copyright © 2014 Elsevier B.V. All rights reserved.

Carbon dioxide capture using covalent organic frameworks (COFs) type material-a theoretical investigation.

PubMed

Dash, Bibek

2018-04-26

The present work deals with a density functional theory (DFT) study of porous organic framework materials containing - groups for CO 2 capture. In this study, first principle calculations were performed for CO 2 adsorption using N-containing covalent organic framework (COFs) models. Ab initio and DFT-based methods were used to characterize the N-containing porous model system based on their interaction energies upon complexing with CO 2 and nitrogen gas. Binding energies (BEs) of CO 2 and N 2 molecules with the polymer framework were calculated with DFT methods. Hybrid B3LYP and second order MP2 methods combined with of Pople 6-31G(d,p) and correlation consistent basis sets cc-pVDZ, cc-pVTZ and aug-ccVDZ were used to calculate BEs. The effect of linker groups in the designed covalent organic framework model system on the CO 2 and N 2 interactions was studied using quantum calculations.

Puzzle of magnetic moments of Ni clusters revisited using quantum Monte Carlo method.

PubMed

Lee, Hung-Wen; Chang, Chun-Ming; Hsing, Cheng-Rong

2017-02-28

The puzzle of the magnetic moments of small nickel clusters arises from the discrepancy between values predicted using density functional theory (DFT) and experimental measurements. Traditional DFT approaches underestimate the magnetic moments of nickel clusters. Two fundamental problems are associated with this puzzle, namely, calculating the exchange-correlation interaction accurately and determining the global minimum structures of the clusters. Theoretically, the two problems can be solved using quantum Monte Carlo (QMC) calculations and the ab initio random structure searching (AIRSS) method correspondingly. Therefore, we combined the fixed-moment AIRSS and QMC methods to investigate the magnetic properties of Ni n (n = 5-9) clusters. The spin moments of the diffusion Monte Carlo (DMC) ground states are higher than those of the Perdew-Burke-Ernzerhof ground states and, in the case of Ni 8-9 , two new ground-state structures have been discovered using the DMC calculations. The predicted results are closer to the experimental findings, unlike the results predicted in previous standard DFT studies.

SERS and DFT study of p-hydroxybenzoic acid adsorbed on colloidal silver particles.

PubMed

Chen, Y; Chen, S J; Li, S; Wei, J J

2015-10-16

In this study, normal Raman spectra of p—hydroxybenzoic acid (PHBA) powder and its surface—enhanced Raman scattering (SERS) spectra in silver colloidal solutions were measured under near infrared excitation conditions. In theoretical calculation, two models of PHBA adsorbed on the surfaces of silver nanoparticles were established. The Raman frequencies of these two models using density functional theory (DFT) method were calculated, and compared with the experimental results. It was found that the calculated Raman frequencies were in good agreement with experimental values, which indicates that there are two enhanced mechanism physical (electromagnetic, EM) enhancement and chemical (charge—transfer, CT) enhancement, in silver colloidal solutions regarding SERS effect. Furthermore, from high—quality SERS spectrum of PHBA obtained in silver colloids, we inferred that PHBA molecules in silver colloids adsorb onto the metal surfaces through carboxyl at a perpendicular orientation. The combination of SERS spectra and DFT calculation is thus useful for studies of the adsorption—orientation of a molecule on a metal colloid.

Infrared vibrational and electronic transitions in the dibenzopolyacene family.

PubMed

Mattioda, Andrew L; Bauschlicher, Charles W; Bregman, Jonathan D; Hudgins, Douglas M; Allamandola, Louis J; Ricca, Alessandra

2014-09-15

We report experimental spectra in the mid-infrared (IR) and near-IR for a series of dibenzoacenes isolated in Ar matrices. The experiments are supported by Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations with both vibrational and electronic transitions studied. For the neutrals, we find good agreement between the experimental and B3LYP and BP86 results for all species studied. The band at about 1440 cm(-1) carries more intensity than in typical PAHs and increases in intensity with the size of the dibenzoacene molecule. For the ions the B3LYP approach fails to yield reasonable IR spectra for most systems and the BP86 approach is used. Electronic transitions dominate the vibrational bands in the mid-IR region for the large dibenzoacene ions. In spite of the very strong electronic transitions, there is still reasonable agreement between theory and experiment for the vibrational band positions. The experimental and theoretical results for the dibenzoacenes are also compared with those for the polyacenes. Published by Elsevier B.V.

Theoretical Study of Effect of Introducing π-Conjugation on Efficiency of Dye-Sensitized Solar Cell.

PubMed

Lee, Geon Hyeong; Kim, Young Sik

2018-09-01

In this study, phenoxazine (PXZ)-based dye sensitizers with triphenylamine (TPA) as a dual-electron donor and thiophen and benzothiadiazole (BTD) or 4,7-diethynylbenzo[c][1,2,5]thiadiazole (DEBT) as an electron acceptor (dye1, dye2, and dye3) were designed and investigated. dye3 can significantly stabilize the lowest unoccupied molecular orbital (LUMO) energy level of an organic dye. We used density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to better understand the factors responsible for the photovoltaic performance. The absorption spectrum of the dyes showed different forms because of the different energy levels of the molecular orbital (MO) of each dye and the intramolecular energy transfer (EnT). Among the three dyes, dye3 showed greater red-shift, broader absorption spectra, and higher molar extinction coefficient. These results indicate that adding a withdrawing unit and π-conjugation to a dye can result in good photovoltaic properties for dye-sensitized solar cells (DSSCs).

Compton profiles and electronic properties of TiB{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhatt, Samir, E-mail: sameerbhatt011@gmail.com; Suthar, K. K.; Ahuja, B. L.

In this paper, we report the experimental Compton profile (CP) of TiB{sub 2} using high energy {sup 137}Cs γ-rays Compton spectrometer. To interpret the experimental momentum density, we have calculated the CPs using Hartree-Fock (HF), density functional theory (DFT) and hybridization of DFT and HF within linear combination of atomic orbitals. The theoretical profile with generalized gradient approximation is found to be relatively in better agreement with the experimental profile. A sharp valley in density of states and hence the pseudogap near the Fermi energy is attributed to hybridization of Ti-3d and B-2p states and almost reverse trend of energymore » bands below and above the Fermi energy.« less

NTO-Picryl Constitutional Isomers—A DFT Study

NASA Astrophysics Data System (ADS)

Türker, Lemi; Çelik Bayar, Çağlar

2012-01-01

The quantum chemical properties and the detonation performance of some new explosives, 5-nitro-4-picryl-2,4-dihydro-3H-1,2,4-triazol-3-one (class A) and 5-nitro-2-picryl-2,4-dihydro-3H-1,2,4-triazol-3-one (class B), and their constitutional isomers have been investigated theoretically using the density functional theory (DFT) 6-31G(d,p) method. All of the constitutional isomers were found to be more sensitive than 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) and TNT but more insensitive than RDX and HMX. Their detonation performance is higher than that of NTO and TNT and all except two had lower detonation performance than RDX and HMX.

Structural, thermodynamic, and electronic properties of Laves-phase NbMn2 from first principles, x-ray diffraction, and calorimetric experiments

NASA Astrophysics Data System (ADS)

Yan, X.; Chen, Xing-Qiu; Michor, H.; Wolf, W.; Witusiewicz, V. T.; Bauer, E.; Podloucky, R.; Rogl, P.

2018-03-01

By combining theoretical density functional theory (DFT) and experimental studies, structural and magnetic phase stabilities and electronic structural, elastic, and vibrational properties of the Laves-phase compound NbMn2 have been investigated for the C14, C15, and C36 crystal structures. At low temperatures C14 is the ground-state structure, with ferromagnetic and antiferromagnetic orderings being degenerate in energy. The degenerate spin configurations result in a rather large electronic density of states at Fermi energy for all magnetic cases, even for the spin-polarized DFT calculations. Based on the DFT-derived phonon dispersions and densities of states, temperature-dependent free energies were derived for the ferromagnetic and antiferromagnetic C14 phase, demonstrating that the spin-configuration degeneracy possibly exists up to finite temperatures. The heat of formation Δ298H0=-45.05 ±3.64 kJ (molf .u .NbMn2) -1 was extracted from drop isoperibolic calorimetry in a Ni bath. The DFT-derived enthalpy of formation of NbMn2 is in good agreement with the calorimetric measurements. Second-order elastic constants for NbMn2 as well as for related compounds were calculated.

Theoretical investigation of the reactivity in the C-F bond activation of CH 3F by Lu + in the gas phase

NASA Astrophysics Data System (ADS)

Liu, Ze-Yu; Wang, Yong-Cheng; Geng, Zhi-Yuan; Yang, Xiao-Yan; Wang, Han-Qing

2006-11-01

The reaction of Lu + with CH 3F, which was selected as a representative system of the activation of C-F bond in fluorohydrocarbons by late lanthanide cations, has been examined using density functional theory (DFT). The potential energy surfaces (PESs) of [Lu, C, H 3, F] + were explored in detail in both singlet and triplet electronic states. The electron-transfer reactivity of the reaction was analyzed using the two-state model, and a strongly avoided crossing behaviour on the transition state (TS) area was shown. The theoretical results can act as a guide to further theoretical and experimental researches.

Laboratory Spectroscopy of Fluorinated Molecules for Atmospheric Physics

NASA Astrophysics Data System (ADS)

Godin, Paul Joseph

Temperature-dependent absorption cross-sections are presented for five fluorinated molecules considered to be greenhouse gases due to being radiatively active in the mid-infrared. The molecules studied are perfluorotributylamine (PFTBA), 2,2,3,3,3- pentafluoropropanol (PFPO), 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), perfluorodecalin (PFDC), and 2H,3H-perfluoropentane (HFC-43-10mee). HFIP is a fluorinated liquid commonly used as a specialty solvent for some polar polymers and in organic synthesis. PFTBA, PFPO, and HFC-43-10mee are commonly used in electronic and industrial applications. PFDC is capable of dissolving large quantities of gases, making it useful for a variety of medical applications. Experimental absorption cross-sections were derived from Fourier transform infrared spectra recorded from 530 to 3400 cm ?1 with a resolution of 0.1 cm ?1 over a temperature range of 298 to 360 K. These results were compared to theoretical density functional theory (DFT) calculations and previously published experimental measurements made at room temperature. Theoretical DFT calculations were performed using the B3LYP method and a minimum basis set of 6-311+G(d,p). The calculations have determined the optimized geometrical configuration, infrared intensities, and wavenumbers of the harmonic frequencies for different ground-state configurations due to the presence of internal rotors. As the population of each configuration changes with temperature, changes in the experimental spectra were used to make accurate band assignments. From these band assignments, the DFT spectra were calibrated to match the experimental spectra, increasing the accuracy of the DFT prediction outside of the experimental range. Using the adjusted DFT-calculated spectra, the wavenumber range was extended beyond the experimental range to calculate radiative efficiencies and global warming potentials. When using only the experimental range, the new values agreed with previously published values. However, when the range was extended using the DFT spectra, the radiative efficiency and global warming potential were increased, suggesting that the current values are underestimating the climate impacts of these species. Additionally, work done on building a multipass White cell is presented. This new system can be used in the future to resolve weak lines to extract line parameters needed for atmospheric trace gas retrievals.

Hydrogen bonding interactions in nicotinamide Ionic Liquids: A comparative spectroscopic and DFT studies

NASA Astrophysics Data System (ADS)

Shukla, Madhulata

2017-03-01

Being biodegradable in nature nicotinamide based Ionic Liquids (ILs) are gaining much attention now a day. Nicotinamide iodide (i.e 1-methyl-3ethoxy carbonyl pyridinium iodide (mNicI)) and 1-methyl-3ethoxy carbonyl pyridinium trifilimide (mNicNTf2) new ILs has been synthesized and has been characterized using different spectroscopic techniques like NMR, UV visible and infrared spectroscopy. Theoretical studies have been performed on several nicotinamide ILs. Geometry and spectral features were further characterized by Density Functional Theory (DFT) calculation. NBO charge distribution and electrostatic potential diagram presents in depth knowledge about interactions between cation and anion. A comparative theoretical study between mNicI and its other analogues i. e 1-methyl-3 ethoxy carbonyl pyridinium chloride and bromide i. e mNicCl and mNicBr has also been performed. Csbnd H⋯X hydrogen bonding along with C⋯X interaction has been reported for the first time for the nicotinamide based ILs. C2sbnd H stretching frequency shifts to higher wavenumber with change to a lesser electronegative anion. mNicCl and mNicBr are expected to be solid in nature with the evidence from the red shift in stretching frequency as compared to mNicI. TD-DFT calculation of mNicI proved that pale yellow color of liquid is due to inherent transition from anion to cation.

A theoretical study on the geometry and spectroscopic properties of ground-state and local minima isomers of (CuS)n=2-6 clusters

NASA Astrophysics Data System (ADS)

Luque-Ceballos, Jonathan C.; Posada-Borbón, Alvaro; Herrera-Urbina, Ronaldo; Aceves, R.; Juárez-Sánchez, J. Octavio; Posada-Amarillas, Alvaro

2018-03-01

Spectroscopic properties of gas-phase copper sulfide clusters (CuS)n (n = 2-6) are calculated using Density Functional Theory (DFT) and time-dependent (TD) DFT approaches. The energy landscape of the potential energy surface is explored through a basin-hopping DFT methodology. Ground-state and low-lying isomer structures are obtained. The global search was performed at the B3PW91/SDD level of theory. Normal modes are calculated to validate the existence of optimal cluster structures. Energetic properties are obtained for the ground-state and isomer clusters and their relative energies are evaluated for probing isomerization. This is a few tenths of an eV, except for (CuS)2 cluster, which presents energy differences of ∼1 eV. Notable differences in the infrared spectra exist between the ground-state and first isomer structures, even for the (CuS)5 cluster, which has in both configurations a core copper pyramid. TDDFT provides the simulated absorption spectrum, presenting a theoretical description of optical absorption bands in terms of electronic excitations in the UV and visible regions. Results exhibit a significant dependence of the calculated UV/vis spectra on clusters size and shape regarding the ground state structures. Optical absorption is strong in the UV region, and weak or forbidden in the visible region of the spectrum.

Vibrational spectra, optical properties, NBO and HOMO-LUMO analysis of L-Phenylalanine L-Phenylalaninium Perchlorate: DFT calculations.

PubMed

Elleuch, Nabil; Ben Ahmed, Ali; Feki, Habib; Abid, Younes; Minot, Christian

2014-01-01

In this work, we report a combined experimental and theoretical study of a nonlinear optical material, L-Phenylalanine L-Phenylalaninium Perchlorate. Single crystals of the title compound have been grown by slow evaporation of an aqueous solution at room temperature. Theoretical calculations were preceded by redetermination of the crystal X-ray structure. The compound crystallizes in the non-centro symmetric space group P2(1)2(1)2(1) of the orthorhombic system. The FT-IR and Raman spectra of the crystal were recorded and analyzed. The density functional theory (DFT) computations have been performed at B3LYP/6-31G(d) level to derive equilibrium geometry, vibrational wavenumbers, intensity and NLO properties. All observed vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our DFT calculations as a primary source of attribution and also by comparison with the previous results for similar compounds. Natural bond orbital analysis was carried out to demonstrate the various inter-and intramolecular interaction that are responsible of the stabilization of the compound. The lowering of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gap appears to be the cause of its enhanced charge transfer interaction leading to high NLO activity. Copyright © 2013 Elsevier B.V. All rights reserved.

On the subsystem formulation of linear-response time-dependent DFT.

PubMed

Pavanello, Michele

2013-05-28

A new and thorough derivation of linear-response subsystem time-dependent density functional theory (TD-DFT) is presented and analyzed in detail. Two equivalent derivations are presented and naturally yield self-consistent subsystem TD-DFT equations. One reduces to the subsystem TD-DFT formalism of Neugebauer [J. Chem. Phys. 126, 134116 (2007)]. The other yields Dyson type equations involving three types of subsystem response functions: coupled, uncoupled, and Kohn-Sham. The Dyson type equations for subsystem TD-DFT are derived here for the first time. The response function formalism reveals previously hidden qualities and complications of subsystem TD-DFT compared with the regular TD-DFT of the supersystem. For example, analysis of the pole structure of the subsystem response functions shows that each function contains information about the electronic spectrum of the entire supersystem. In addition, comparison of the subsystem and supersystem response functions shows that, while the correlated response is subsystem additive, the Kohn-Sham response is not. Comparison with the non-subjective partition DFT theory shows that this non-additivity is largely an artifact introduced by the subjective nature of the density partitioning in subsystem DFT.

Role of exact exchange in thermally-assisted-occupation density functional theory: A proposal of new hybrid schemes.

PubMed

Chai, Jeng-Da

2017-01-28

We propose hybrid schemes incorporating exact exchange into thermally assisted-occupation-density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] for an improved description of nonlocal exchange effects. With a few simple modifications, global and range-separated hybrid functionals in Kohn-Sham density functional theory (KS-DFT) can be combined seamlessly with TAO-DFT. In comparison with global hybrid functionals in KS-DFT, the resulting global hybrid functionals in TAO-DFT yield promising performance for systems with strong static correlation effects (e.g., the dissociation of H 2 and N 2 , twisted ethylene, and electronic properties of linear acenes), while maintaining similar performance for systems without strong static correlation effects. Besides, a reasonably accurate description of noncovalent interactions can be efficiently achieved through the inclusion of dispersion corrections in hybrid TAO-DFT. Relative to semilocal density functionals in TAO-DFT, global hybrid functionals in TAO-DFT are generally superior in performance for a wide range of applications, such as thermochemistry, kinetics, reaction energies, and optimized geometries.

Spectroscopic and molecular structure investigation of 2-furanacrylic acid monomer and dimer using HF and DFT methods

NASA Astrophysics Data System (ADS)

Ghalla, H.; Issaoui, N.; Govindarajan, M.; Flakus, H. T.; Jamroz, M. H.; Oujia, B.

2014-02-01

In the present work, we reported a combined experimental and theoretical study on molecular structure and vibrational spectra of 2-furanacrylic acid (abbreviated as 2FAA). The FT-IR and FT-Raman spectra of 2FAA have been recorded in the regions 4000-400 and 4000-100 cm-1. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The monomer and dimer structures of the title molecule have been obtained from Hartree-Fock (HF) and density functional theory (DFT) B3LYP methods with 6-311++G(d,p) as basis set calculations. The vibrational frequencies were calculated by DFT method and compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. Intermolecular OH⋯O hydrogen bonds are discussed in dimer structure of the molecule. The infrared and Raman spectra were also predicted from the calculated intensities. The polarizability and first order hyperpolarizabilty of the title molecule were calculated and interpreted. A study on the electronic properties, such as excitation energies, oscillator strength, wavelengths, HOMO and LUMO energies, are performed by time-dependent DFT (TD-DFT) approach. In addition, Milliken atomic charges, possible charge transfer, natural bond orbital (NBO) and AIM topological analysis were performed. Moreover, molecular electrostatic potential (MEP) and the thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase.

Vibrational, structural and electronic properties investigation by DFT calculations and molecular docking studies with DNA topoisomerase II of strychnobrasiline type alkaloids: A theoretical approach for potentially bioactive molecules

NASA Astrophysics Data System (ADS)

Costa, Renyer A.; Oliveira, Kelson M. T.; Costa, Emmanoel Vilaça; Pinheiro, Maria L. B.

2017-10-01

A combined experimental and theoretical DFT study of the structural, vibrational and electronic properties of strychnobrasiline and 12-hydroxy-10,11-dimethoxystrychnobrasiline is presented using the Becke three-parameter Lee-Yang-Parr function (B3LYP) and 6-311G(2d,p) basis set. The theoretical geometry optimization data were compared with the X-ray data for a similar structure in the associated literature, showing close values. The calculated HOMO-LUMO gap values showed that the presence of substituents in the benzene ring influences the quantum properties which are directly related to the reactive properties. Theoretical UV spectra agreed well with the measured experimental data, with bands assigned. In addition, Natural Bond Orbitals (NBOs), Mapped molecular electrostatic potential surface (MEPS) and NLO calculations were also performed at the same theory level. The theoretical vibrational analysis revealed several characteristic vibrations that may be used as a diagnostic tool for other strychnobrasiline type alkaloids, simplifying their identification and structural characterization. Molecular docking calculations with DNA Topoisomerase II-DNA complex showed binding free energies values of -8.0 and -9.5 kcal/mol for strychnobrasiline and 12-hydroxy-10,11-dimethoxystrychnobrasiline respectively, while for amsacrine, used for the treatment of leukemia, the binding free energy ΔG presented a value of -10.0 kcal/mol, suggesting that strychnobrasiline derivative alkaloids might exhibit an antineoplastic activity.

Vibrational spectroscopy and DFT calculations of flavonoid derriobtusone A

NASA Astrophysics Data System (ADS)

Marques, A. N. L.; Mendes Filho, J.; Freire, P. T. C.; Santos, H. S.; Albuquerque, M. R. J. R.; Bandeira, P. N.; Leite, R. V.; Braz-Filho, R.; Gusmão, G. O. M.; Nogueira, C. E. S.; Teixeira, A. M. R.

2017-02-01

Flavonoids are secondary metabolites of plants which perform various functions. One subclass of flavonoid is auronol that can present immunostimulating activity. In this work Fourier-Transform Infrared with Attenuated Total Reflectance (FTIR-ATR) and Fourier-Transform Raman (FT-Raman) spectra of an auronol, derriobtusone A (C18H12O4), were obtained at room temperature. Theoretical calculations using Density Functional Theory (DFT) were performed in order to assign the normal modes and to interpret the spectra of the derriobtusone A molecule. The FTIR-ATR and FT-Raman spectra of the crystal, were recorded at room temperature in the regions 600 cm-1 to 4000 cm-1 and 40 cm-1 to 4000 cm-1, respectively. The normal modes of vibrations were obtained using Density Functional Theory with B3LYP functional and 6-31G+ (d,p) basis set. The calculated frequencies are in good agreement with those obtained experimentally. Detailed assignments of the normal modes present in both the Fourier-Transform infrared and the Fourier-Transform Raman spectra of the crystal are given.

Novel MC/BZY Proton Conductor: Materials Development, Device Evaluation, and Theoretical Exploration using CI and DFT Methods

DTIC Science & Technology

2017-09-05

Report: Novel MC/BZY Proton Conductor: Materials Development, Device Evaluation, and Theoretical Exploration using CI and DFT Methods The views...policy or decision, unless so designated by other documentation. 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS (ES) U.S. Army Research Office P.O...Box 12211 Research Triangle Park, NC 27709-2211 REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 10. SPONSOR/MONITOR’S ACRONYM(S

Time-dependent density functional theory (TD-DFT) coupled with reference interaction site model self-consistent field explicitly including spatial electron density distribution (RISM-SCF-SEDD)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yokogawa, D., E-mail: d.yokogawa@chem.nagoya-u.ac.jp; Institute of Transformative Bio-Molecules

2016-09-07

Theoretical approach to design bright bio-imaging molecules is one of the most progressing ones. However, because of the system size and computational accuracy, the number of theoretical studies is limited to our knowledge. To overcome the difficulties, we developed a new method based on reference interaction site model self-consistent field explicitly including spatial electron density distribution and time-dependent density functional theory. We applied it to the calculation of indole and 5-cyanoindole at ground and excited states in gas and solution phases. The changes in the optimized geometries were clearly explained with resonance structures and the Stokes shift was correctly reproduced.

Anatase-rutile phase transformation of titanium dioxide bulk material: a DFT + U approach

NASA Astrophysics Data System (ADS)

Vu, Nam H.; Le, Hieu V.; Cao, Thi M.; Pham, Viet V.; Le, Hung M.; Nguyen-Manh, Duc

2012-10-01

The anatase-rutile phase transformation of TiO2 bulk material is investigated using a density functional theory (DFT) approach in this study. According to the calculations employing the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional with the Vanderbilt ultrasoft pseudopotential, it is suggested that the anatase phase is more energetically stable than rutile, which is in variance with the experimental observations. Consequently, the DFT + U method is employed in order to predict the correct structural stability in titania from electronic-structure-based total energy calculations. The Hubbard U term is determined by examining the band structure of rutile with various values of U from 3 to 10 eV. At U = 5 eV, a theoretical bandgap for rutile is obtained as 3.12 eV, which is in very good agreement with the reported experimental bandgap. Hence, we choose the DFT + U method (with U = 5 eV) to investigate the transformation pathway using the newly-developed solid-state nudged elastic band (ss-NEB) method, and consequently obtain an intermediate transition structure that is 9.794 eV per four-TiO2 above the anatase phase. When the Ti-O bonds in the transition state are examined using charge density analysis, seven Ti-O bonds (out of 24 bonds in the anatase unit cell) are broken, and this result is in excellent agreement with a previous experimental study (Penn and Banfield 1999 Am. Miner. 84 871-6).

Synthesis of 4-((1E, 6E)-7-(4-hydroxy-3-methoxyphenyl)-3, 5-dioxohepta-1, 6-dienyl)-2-methoxyphenyl 4-fluorobenzoate, a novel monoester derivative of curcumin, its experimental and theoretical (DFT) studies

NASA Astrophysics Data System (ADS)

Srivastava, Sangeeta; Gupta, Preeti; Amandeep; Singh, Ranvijay Pratap

2016-04-01

Curcumin (1), isolated as a major component from the chloroform extract of Curcuma longa was converted to its ester derivative 4-((1E, 6E)-7-(4-hydroxy-3-methoxyphenyl)-3,5-dioxohepta-1,6-dienyl)-2-methoxyphenyl 4-fluorobenzoate (2). The compound has been characterized with the help of 1H, 13C NMR, UV, IR and mass spectrometry. The molecular geometry of synthesized compound was calculated in ground state by Density functional theory (DFT/B3LYP) using 6-31G (d,p) basis set. 1H and 13C NMR chemical shifts were calculated in ground state by using Gauge-Including Atomic Orbital (GIAO) approach and these values were correlated with experimental observations. The electronic properties such as HOMO and LUMO energies were calculated using time dependent Density Functional Theory (TD-DFT). Stability of the molecule as a result of hyper conjugative interactions and electron delocalization were analysed using Natural bond orbital (NBO) analysis. Intramolecular interactions were analysed by AIM (Atom in molecule) approach. Global reactivity descriptors were calculated to study the reactive site within molecule. The vibrational wavenumbers were calculated using DFT method and assigned with the help of potential energy distribution (PED). First hyperpolarizability values have been calculated to describe the nonlinear optical (NLO) property of the synthesized compounds. Molecular electrostatic potential (MEP) analysis has also been carried out.

Synthesis, spectroscopic characterization, DFT studies and antifungal activity of (E)-4-amino-5-[N'-(2-nitro-benzylidene)-hydrazino]-2,4-dihydro-[1,2,4]triazole-3-thione

NASA Astrophysics Data System (ADS)

Joshi, Rachana; Pandey, Nidhi; Yadav, Swatantra Kumar; Tilak, Ragini; Mishra, Hirdyesh; Pokharia, Sandeep

2018-07-01

The hydrazino Schiff base (E)-4-amino-5-[N'-(2-nitro-benzylidene)-hydrazino]-2,4-dihydro-[1,2,4]triazole-3-thione was synthesized and structurally characterized by elemental analysis, FT-IR, Raman, 1H and 13C-NMR and UV-Vis studies. A density functional theory (DFT) based electronic structure calculations were accomplished at B3LYP/6-311++G(d,p) level of theory. A comparative analysis of calculated vibrational frequencies with experimental vibrational frequencies was carried out and significant bands were assigned. The results indicate a good correlation (R2 = 0.9974) between experimental and theoretical IR frequencies. The experimental 1H and 13C-NMR resonance signals were also compared to the calculated values. The theoretical UV-Vis spectral studies were carried out using time dependent-DFT method in gas phase and IEFPCM model in solvent field calculation. The geometrical parameters were calculated in the gas phase. Atomic charges at selected atoms were calculated by Mulliken population analysis (MPA), Hirshfeld population analysis (HPA) and Natural population analysis (NPA) schemes. The molecular electrostatic potential (MEP) map was calculated to assign reactive site on the surface of the molecule. The conceptual-DFT based global and local reactivity descriptors were calculated to obtain an insight into the reactivity behaviour. The frontier molecular orbital analysis was carried out to study the charge transfer within the molecule. The detailed natural bond orbital (NBO) analysis was performed to obtain an insight into the intramolecular conjugative electronic interactions. The titled compound was screened for in vitro antifungal activity against four fungal strains and the results obtained are explained through in silico molecular docking studies.

FT-IR, UV-vis, 1H and 13C NMR spectra and the equilibrium structure of organic dye molecule disperse red 1 acrylate: a combined experimental and theoretical analysis.

PubMed

Cinar, Mehmet; Coruh, Ali; Karabacak, Mehmet

2011-12-01

This study reports the characterization of disperse red 1 acrylate compound by spectral techniques and quantum chemical calculations. The spectroscopic properties were analyzed by FT-IR, UV-vis, (1)H NMR and (13)C NMR techniques. FT-IR spectrum in solid state was recorded in the region 4000-400 cm(-1). The UV-vis absorption spectrum of the compound that dissolved in methanol was recorded in the range of 200-800 nm. The (1)H and (13)C NMR spectra were recorded in CDCl(3) solution. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational wavenumbers were calculated and scaled values were compared with experimental FT-IR spectrum. A satisfactory consistency between the experimental and theoretical spectra was obtained and it shows that the hybrid DFT method is very useful in predicting accurate vibrational structure, especially for high-frequency region. The complete assignments were performed on the basis of the experimental results and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. A study on the electronic properties were performed by timedependent DFT (TD-DFT) and CIS(D) approach. To investigate non linear optical properties, the electric dipole moment μ, polarizability α, anisotropy of polarizability Δα and molecular first hyperpolarizability β were computed. The linear polarizabilities and first hyperpolarizabilities of the studied molecule indicate that the compound can be a good candidate of nonlinear optical materials. Copyright © 2011 Elsevier B.V. All rights reserved.

Spectroscopic (FT-IR, FT-Raman, UV and NMR) investigation and NLO, HOMO-LUMO, NBO analysis of organic 2,4,5-trichloroaniline.

PubMed

Govindarajan, M; Karabacak, M; Periandy, S; Tanuja, D

2012-11-01

In this work, the experimental and theoretical study on the molecular structure and vibrational spectra of 2,4,5-trichloroaniline (C(6)H(4)NCl(3), abbreviated as 2,4,5-TClA) were studied. The FT-IR and FT-Raman spectra were recorded. The molecular geometry and vibrational frequencies in the ground state were calculated by using the Hartree-Fock (HF) and density functional theory (DFT) methods (B3LYP) with 6-311++G(d,p) basis set. Comparison of the observed fundamental vibrational frequencies of 2,4,5-TClA with calculated results by HF and DFT indicates that B3LYP is superior to HF method for molecular vibrational problems. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The theoretically predicted FT-IR and FT-Raman spectra of the title molecule have been constructed. A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. Besides, molecular electrostatic potential (MEP) and thermodynamic properties were performed. The electric dipole moment (μ) and the first hyperpolarizability (β) values of the investigated molecule were computed using ab initio quantum mechanical calculations. The calculated results also show that the 2,4,5-TClA molecule may have microscopic nonlinear optical (NLO) behavior with non-zero values. Mulliken atomic charges of 2,4,5-TClA was calculated and compared with aniline and chlorobenzene molecules. The (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. Copyright © 2012 Elsevier B.V. All rights reserved.

Abs-initio, Predictive Calculations for Optoelectronic and Advanced Materials Research

NASA Astrophysics Data System (ADS)

Bagayoko, Diola

2010-10-01

Most density functional theory (DFT) calculations find band gaps that are 30-50 percent smaller than the experimental ones. Some explanations of this serious underestimation by theory include self-interaction and the derivative discontinuity of the exchange correlation energy. Several approaches have been developed in the search for a solution to this problem. Most of them entail some modification of DFT potentials. The Green function and screened Coulomb approximation (GWA) is a non-DFT formalism that has led to some improvements. Despite these efforts, the underestimation problem has mostly persisted in the literature. Using the Rayleigh theorem, we describe a basis set and variational effect inherently associated with calculations that employ a linear combination of atomic orbitals (LCAO) in a variational approach of the Rayleigh-Ritz type. This description concomitantly shows a source of large underestimation errors in calculated band gaps, i.e., an often dramatic lowering of some unoccupied energies on account of the Rayleigh theorem as opposed to a physical interaction. We present the Bagayoko, Zhao, and Williams (BZW) method [Phys. Rev. B 60, 1563 (1999); PRB 74, 245214 (2006); and J. Appl. Phys. 103, 096101 (2008)] that systematically avoids this effect and leads (a) to DFT and LDA calculated band gaps of semiconductors in agreement with experiment and (b) theoretical predictions of band gaps that are confirmed by experiment. Unlike most calculations, BZW computations solve, self-consistently, a system of two coupled equations. DFT-BZW calculated effective masses and optical properties (dielectric functions) also agree with measurements. We illustrate ten years of success of the BZW method with its results for GaN, C, Si, 3C-SIC, 4H-SiC, ZnO, AlAs, Ge, ZnSe, w-InN, c-InN, InAs, CdS, AlN and nanostructures. We conclude with potential applications of the BZW method in optoelectronic and advanced materials research.

Electron correlation and the self-interaction error of density functional theory

NASA Astrophysics Data System (ADS)

Polo, Victor; Kraka, Elfi; Cremer, Dieter

The self-interaction error (SIE) of commonly used DFT functionals has been systematically investigated by comparing the electron density distribution ρ( r ) generated by self-interaction corrected DFT (SIC-DFT) with a series of reference densities obtained by DFT or wavefunction theory (WFT) methods that cover typical electron correlation effects. Although the SIE of GGA functionals is considerably smaller than that of LDA functionals, it has significant consequences for the coverage of electron correlation effects at the DFT level of theory. The exchange SIE mimics long range (non-dynamic) pair correlation effects, and is responsible for the fact that the electron density of DFT exchange-only calculations resembles often that of MP4, MP2 or even CCSD(T) calculations. Changes in the electron density caused by SICDFT exchange are comparable with those that are associated with HF exchange. Correlation functionals contract the density towards the bond and the valence region, thus taking negative charge out of the van der Waals region where these effects are exaggerated by the influence of the SIE of the correlation functional. Hence, SIC-DFT leads in total to a relatively strong redistribution of negative charge from van der Waals, non-bonding, and valence regions of heavy atoms to the bond regions. These changes, although much stronger, resemble those obtained when comparing the densities of hybrid functionals such as B3LYP with the corresponding GGA functional BLYP. Hence, the balanced mixing of local and non-local exchange and correlation effects as it is achieved by hybrid functionals mimics SIC-DFT and can be considered as an economic way to include some SIC into standard DFT. However, the investigation shows also that the SIC-DFT description of molecules is unreliable because the standard functionals used were optimized for DFT including the SIE.

Kinetic theory for strongly coupled Coulomb systems

NASA Astrophysics Data System (ADS)

Dufty, James; Wrighton, Jeffrey

2018-01-01

The calculation of dynamical properties for matter under extreme conditions is a challenging task. The popular Kubo-Greenwood model exploits elements from equilibrium density-functional theory (DFT) that allow a detailed treatment of electron correlations, but its origin is largely phenomenological; traditional kinetic theories have a more secure foundation but are limited to weak ion-electron interactions. The objective here is to show how a combination of the two evolves naturally from the short-time limit for the generator of the effective single-electron dynamics governing time correlation functions without such limitations. This provides a theoretical context for the current DFT-related approach, the Kubo-Greenwood model, while showing the nature of its corrections. The method is to calculate the short-time dynamics in the single-electron subspace for a given configuration of the ions. This differs from the usual kinetic theory approach in which an average over the ions is performed as well. In this way the effective ion-electron interaction includes strong Coulomb coupling and is shown to be determined from DFT. The correlation functions have the form of the random-phase approximation for an inhomogeneous system but with renormalized ion-electron and electron-electron potentials. The dynamic structure function, density response function, and electrical conductivity are calculated as examples. The static local field corrections in the dielectric function are identified in this way. The current analysis is limited to semiclassical electrons (quantum statistical potentials), so important quantum conditions are excluded. However, a quantization of the kinetic theory is identified for broader application while awaiting its detailed derivation.

Stabilization of diketo tautomer of curcumin by premicellar anionic surfactants: UV-Visible, fluorescence, tensiometric and TD-DFT evidences

NASA Astrophysics Data System (ADS)

Dutta, Anisha; Boruah, Bornali; Manna, Arun K.; Gohain, Biren; Saikia, Palash M.; Dutta, Robin K.

2013-03-01

A newly observed UV band of aqueous curcumin, a biologically important molecule, in presence of anionic surfactants, viz., sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), and sodium dodecylsulfonate (SDSN) in buffered aqueous solutions has been studied experimentally and theoretically. The 425 nm absorption band of curcumin disappears and a new UV-band is observed at 355 nm on addition of the surfactants in the submicellar concentration range which is reversed as the surfactant concentration approaches the critical micelle concentration (CMC). The observed spectral absorption, fluorescence intensity and surface tension behavior, under optimal experimental conditions of submicellar concentration ranges of the surfactants in the pH range of 2.00-7.00, indicate that the new band is due to the β-diketo tautomer of curcumin stabilized by interactions between curcumin and the anionic surfactants. The stabilization of the diketo tautomer by submicellar anionic surfactants described here as well as by submicellar cationic surfactant, reported recently, is unique as this is the only such behavior observed in presence of submicellar surfactants of both charge types. The experimental results are in good agreement with the theoretical calculations using ab initio density functional theory combined with time dependent density functional theory (TD-DFT) calculations.

Probing the structural evolution of ruthenium doped germanium clusters: Photoelectron spectroscopy and density functional theory calculations

PubMed Central

Jin, Yuanyuan; Lu, Shengjie; Hermann, Andreas; Kuang, Xiaoyu; Zhang, Chuanzhao; Lu, Cheng; Xu, Hongguang; Zheng, Weijun

2016-01-01

We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen− (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen− clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen−/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters. PMID:27439955

Spectral analysis, vibrational assignments, NBO analysis, NMR, UV-Vis, hyperpolarizability analysis of 2-aminofluorene by density functional theory.

PubMed

Jone Pradeepa, S; Sundaraganesan, N

2014-05-05

In this present investigation, the collective experimental and theoretical study on molecular structure, vibrational analysis and NBO analysis has been reported for 2-aminofluorene. FT-IR spectrum was recorded in the range 4000-400 cm(-1). FT-Raman spectrum was recorded in the range 4000-50 cm(-1). The molecular geometry, vibrational spectra, and natural bond orbital analysis (NBO) were calculated for 2-aminofluorene using Density Functional Theory (DFT) based on B3LYP/6-31G(d,p) model chemistry. (13)C and (1)H NMR chemical shifts of 2-aminofluorene were calculated using GIAO method. The computed vibrational and NMR spectra were compared with the experimental results. The total energy distribution (TED) was derived to deepen the understanding of different modes of vibrations contributed by respective wavenumber. The experimental UV-Vis spectra was recorded in the region of 400-200 nm and correlated with simulated spectra by suitably solvated B3LYP/6-31G(d,p) model. The HOMO-LUMO energies were measured with time dependent DFT approach. The nonlinearity of the title compound was confirmed by hyperpolarizabilty examination. Using theoretical calculation Molecular Electrostatic Potential (MEP) was investigated. Copyright © 2014 Elsevier B.V. All rights reserved.

Determination of Structural and Vibrational Properties of 5-QUINOLINECARBOXALDEHYDE Using Experimental Ft-Ir Ft-Raman Techniques and Theoretical HF and DFT Methods

NASA Astrophysics Data System (ADS)

Kumru, Mustafa; Kocademir, Mustafa; Bardakci, Tayyibe

2013-06-01

Quinoline derivatives have been used in several pharmaceuticals. They have vital roles in regulating the functions of DNA and cancerous cells. It's necessary to determine the structures and spectroscopic properties of quinoline derivates. In this study, the FT-IR (including mid and far regions) and FT-Raman spectra of 5-quinolinecarboxaldehyde have been investigated. Hartree-Fock (HF) and density functional B3LYP calculations have also been employed with the 6-311++G(d,p) basis set for investigating the structural and spectroscopic properties of the cis and trans conformers of 5-quinolinecarboxaldehyde. Experimental and theoretical results have been compared and the results are in good agreement with each other. Keywords: 5-quinolinecarboxaldehyde; Vibrational Spectroscopy; FT-IR spectra; FT-Raman spectra; Vibrational Modes; HF; DFT [1] V. Kucuk, A. Altun, M. Kumru, Spectrochim. Acta Part A 85(2012)92-98 [2] M. Kumru, V. Kucuk, T. Bardakci, Spectrochim. Acta Part A 90(2012)28-34 [3] M. Kumru, V. Kucuk, M. Kocademir, Spectrochim. Acta Part A, 96 (2012) 242-251 We thank the Turkish Scientific and Technical Research Council (TUBITAK) for their financial support through National Postdoctoral Research Scholarship Programme and Scientific Research Fund of Fatih University under the project number P50011001 G (1457).

Microwave-assisted synthesis, structural characterization, DFT studies, antibacterial and antioxidant activity of 2-methyl-4-oxo-1,2,3,4-tetrahydroquinazoline-2-carboxylic acid

NASA Astrophysics Data System (ADS)

Obafemi, Craig A.; Fadare, Olatomide A.; Jasinski, Jerry P.; Millikan, Sean P.; Obuotor, Efere M.; Iwalewa, Ezekiel O.; Famuyiwa, Samson O.; Sanusi, Kayode; Yilmaz, Yusuf; Ceylan, Ümit

2018-03-01

In the present study a new tetrahydroquinazoline-2-carboxylic, C10H10N2O3, 1‧, was synthesized and its structure was characterized by elemental analysis, IR, 1H NMR, 13C NMR data and high-resolution mass spectrometry. The spectral results are in line with the proposed structure. Single crystal X-ray structural analysis of the compound showed that the crystal structure adopts a monoclinic space group P21/c, with the packing of the molecule stabilized by Cdbnd O … …Hsbnd O, Nsbnd H … ….Odbnd Csbnd Osbnd intermolecular hydrogen bonding. The theoretical geometrical parameters of the compound have been calculated using density functional (DFT) and time-dependent density functional (TD-DFT) theory methods and have been used to predict the thermodynamic one-electron redox potential and the electronic absorption property of the compound. The theoretical characterization matched the experimental measurements, showing a good correlation. The calculated HOMO-LUMO gap (4.79 eV) suggests that compound 1‧ could be a potential antioxidant. The synthesized compound was screened for its in vitro antimicrobial activity against selected bacterial strains and antioxidant activity using the TAC, FRAP, NO and ABTS models. In vitro antioxidant activity of 1' showed a moderate activity, but weaker scavenging activity than the standards of ascorbic acid and trolox. Results of the antibacterial activity of the tested compound showed that it possesses a higher activity against Bacillus anthracis, Bacillus cereus, Bacillus polymyxa, Bacillus subtilis and Staphylococcus aureus than the two standard drugs, streptomycin and tetracycline, and better activity than tetracycline against Escherichia coli.

Electronic states of aryl radical functionalized graphenes: Density functional theory study

NASA Astrophysics Data System (ADS)

Tachikawa, Hiroto; Kawabata, Hiroshi

2016-06-01

Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz) n (n = 1-4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR-(Bz) n (n = 1-4) showed that the aryl radical binds to the carbon atom of GR, and a C-C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol-1 at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol-1. The electronic states of GR-(Bz) n were examined on the basis of theoretical results.

Theoretical and experimental studies of 3β-acetoxy-5α-cholestan-6-one oxime

NASA Astrophysics Data System (ADS)

Khan, Azhar U.; Avecillia, Fernando; Malik, Nazia; Khan, Md. Shahzad; Khan, Mohd Shahid; Mushtaque, Md.

2016-10-01

Steroidal oxime (3β-acetoxy-5α-cholestan- 6-one oxime) has been synthesized using microwave-induced reaction in 3.5 min using saturated steroidal ketone and aqueous hydroxylamine hydrochloride in ethanol. The structure of the compound was elucidated by UV, IR, 1H NMR and X-ray single crystal structure. The computational quantum chemical studies like, IR, UV analysis were performed by density functional theory (DFT) at Becke-3-Lee-Yang-Parr(B3LYP) exchange-correlation functional in combination with 6-31++G(d,p) basis sets. The harmonic vibrational frequencies, the optimized geometric parameters have been interpreted and compared with experimental values. Theoretical wavelength at 214.88 cm-1 correspond to the experimental value 214.0 cm-1. The nature of this transition is n → π*. The theoretical results are in good agreement with experiment results.

A combined experimental and theoretical studies on FT-IR, FT-Raman and UV-vis spectra of 2-chloro-3-quinolinecarboxaldehyde

NASA Astrophysics Data System (ADS)

Prasad, M. V. S.; Udaya Sri, N.; Veeraiah, V.

2015-09-01

In the present study, the FT-IR and FT-Raman spectra of 2-chloro-3-quinolinecarboxaldehyde (2Cl3QC) have been recorded in the region 4000-400 and 3500-50 cm-1, respectively. The fundamental modes of vibrational frequencies of 2Cl3QC are assigned. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy, have been calculated for the molecule. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good non-linear optical (NLO) behavior. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization have been analyzed using natural bond orbitals (NBO) analysis. The results show that charge in electron density (ED) in the π∗ antibonding orbitals and E(2) energies confirms the occurrence of ICT (intra-molecular charge transfer) within the molecule. UV-visible spectrum of the title molecule has also been calculated using TD-DFT/CAM-B3LYP/6-31G(d,p) method. The calculated energy and oscillator strength almost exactly reproduces reported experimental data.

A combined experimental and theoretical studies on FT-IR, FT-Raman and UV-vis spectra of 2-chloro-3-quinolinecarboxaldehyde.

PubMed

Prasad, M V S; Udaya Sri, N; Veeraiah, V

2015-09-05

In the present study, the FT-IR and FT-Raman spectra of 2-chloro-3-quinolinecarboxaldehyde (2Cl3QC) have been recorded in the region 4000-400 and 3500-50 cm(-1), respectively. The fundamental modes of vibrational frequencies of 2Cl3QC are assigned. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy, have been calculated for the molecule. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good non-linear optical (NLO) behavior. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization have been analyzed using natural bond orbitals (NBO) analysis. The results show that charge in electron density (ED) in the π(∗) antibonding orbitals and E((2)) energies confirms the occurrence of ICT (intra-molecular charge transfer) within the molecule. UV-visible spectrum of the title molecule has also been calculated using TD-DFT/CAM-B3LYP/6-31G(d,p) method. The calculated energy and oscillator strength almost exactly reproduces reported experimental data. Copyright © 2015 Elsevier B.V. All rights reserved.

Tailored Rh surface facilitates, enhancement of Raman scattering in trimetallic AuPt core/Rh shell composites: Experimental and theoretical evidences

NASA Astrophysics Data System (ADS)

Loganathan, B.; Chandraboss, V. L.; Senthilvelan, S.; Karthikeyan, B.

2016-01-01

We present a detailed analysis of surface-enhanced Raman scattering of 7-azaindole and L-cysteine adsorbed on a tailored Rh surface by using experimental and density functional theoretical (DFT) calculations. DFT with the B3LYP/Lanl2DZ basis set was used for the optimization of the ground state geometries and simulation of the surface-enhanced Raman spectrum of probe molecules adsorbed on Rh6 cluster. 7-azaindole and L-cysteine adsorption at the shell interface was ascertained from first-principles. In addition, characterization of synthesized trimetallic AuPt core/Rh shell colloidal nanocomposites has been analyzed by UV-visible spectroscopy, high-resolution transmission and scanning electron microscopy, selected area electron diffraction pattern analysis, energy-dispersive X-ray spectroscopy, atomic force, confocal Raman microscopy, FT-Raman and surface-enhanced Raman spectroscopic analysis. This analysis serves as the first step in gaining an accurate understanding of specific interactions at the interface of organic and biomolecules and to gain knowledge on the surface composition of trimetallic Au/Pt/Rh colloidal nanocomposites.

The Effects of Heteroatoms Si and S on Tuning the Optical Properties of Rhodamine- and Fluorescein-Based Fluorescence Probes: A Theoretical Analysis.

PubMed

Zhou, Panwang; Ning, Cai; Alsaedi, Ahmed; Han, Keli

2016-10-05

The effects of the incorporated heteroatoms Si and S on tuning the optical properties of rhodamine- and fluorescein-based fluorescence probes is investigated using DFT and time-dependent DFT with four different functionals. As previously proposed, the large redshift (90 nm) produced by a Si atom in both the absorption and emission spectra can be attributed to the σ*-π* conjugation between the σ* orbital of the Si atom and the π* orbital of the adjacent carbon atoms. However, the presence of a Si atom does not alter the fluorescence quenching mechanism of the nonfluorescent forms of the investigated compounds. For the first time, these theoretical results indicate that the n orbital of the S atom plays an important role in determining the optical properties of the nonfluorescent form of rhodamine-based fluorescence probes. It alters the fluorescence quenching mechanism by lowering the energy of the dark nπ* state, which is due to breakage of the C10-S52 bond upon photoexcitation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical Assessment of Norfloxacin Redox and Photochemistry

NASA Astrophysics Data System (ADS)

Musa, Klefah A. K.; Eriksson, Leif A.

2009-09-01

Norfloxacin, 1-ethyl-6-fluoro-1,4-dihydo-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid, NOR, is an antibiotic drug from the fluoroquinoline family. The different protonation states of this drug formed throughout the pH range is studied by means of density functional theory (DFT) and the spectra of the NOR species computed using time-dependent DFT. Details about their photochemistry are obtained from investigating the highest occupied and lowest unoccupied molecular orbitals. The predominant species under physiological pH, the zwitterion, is the most photoliable one, capable of producing singlet oxygen or/and superoxide radical anions from its triplet state. In addition, the main photodegradation step, defluorination, occurs more easily from this species compared with the other forms. The defluorination from the excited triplet state requires passing a barrier of 16.3 kcal/mol in the case of the zwitterion. The neutral and cationic forms display higher transition barriers, whereas the reaction path of defluorination is completely endothermic for the anionic species. The theoretical results obtained herein are in line with previous experimental data.

Molecular properties via a subsystem density functional theory formulation: a common framework for electronic embedding.

PubMed

Höfener, Sebastian; Gomes, André Severo Pereira; Visscher, Lucas

2012-01-28

In this article, we present a consistent derivation of a density functional theory (DFT) based embedding method which encompasses wave-function theory-in-DFT (WFT-in-DFT) and the DFT-based subsystem formulation of response theory (DFT-in-DFT) by Neugebauer [J. Neugebauer, J. Chem. Phys. 131, 084104 (2009)] as special cases. This formulation, which is based on the time-averaged quasi-energy formalism, makes use of the variation Lagrangian techniques to allow the use of non-variational (in particular: coupled cluster) wave-function-based methods. We show how, in the time-independent limit, we naturally obtain expressions for the ground-state DFT-in-DFT and WFT-in-DFT embedding via a local potential. We furthermore provide working equations for the special case in which coupled cluster theory is used to obtain the density and excitation energies of the active subsystem. A sample application is given to demonstrate the method. © 2012 American Institute of Physics

Densely-packed ZnTPPs Monolayer on the Rutile TiO2(110)-(1×1) Surface: Adsorption Behavior and Energy Level Alignment

PubMed Central

Rangan, Sylvie; Ruggieri, Charles; Bartynski, Robert; Martínez, José Ignacio; Flores, Fernando; Ortega, José

2016-01-01

The adsorption of a densely packed Zinc(II) tetraphenylporphyrin monolayer on a rutile TiO2(110)-(1×1) surface has been studied using a combination of experimental and theoretical methods, aimed at analyzing the relation between adsorption behavior and barrier height formation. The adsorption configuration of ZnTPP was determined from scanning tunnel microscopy (STM) imaging, density functional theory (DFT) calculations and STM image simulation. The corresponding energy alignment was experimentally determined from X-ray and UV-photoemission spectroscopies and inverse photoemission spectroscopy. These results were found in good agreement with an appropriately corrected DFT model, pointing to the importance of local bonding and intermolecular interactions in the establishment of barrier heights. PMID:26998188

COMPARATIVE STUDY OF THREE FUNDAMENTAL ORGANIC COMPOUNDS OF CHAIN STRUCTURE OF THREE RINGS An approach based in the molecular descriptors of the DFT (Density Functional Theory)

NASA Astrophysics Data System (ADS)

Leon, Neira B. Oscar; Fabio, Mejía Elio; Elizabeth, y. Rincón B.

2008-04-01

The organic molecules of a chain structure containing phenyl, oxazole and oxadiazole rings are used in different combinations as active media for tunable lasers. From this viewpoint, we focused in the theoretical study of organic compounds of three rings, which have similar optical properties (fluorescence and laser properties). The main goal of this study is to compare the electronic structure through the analysis of molecular global descriptors defined in the DFT framework of2-[2-X-phenyl]-5-phenyl-1,3-Oxazole, 2-[2-X-phenyl]-5-phenyl-1,3,4-Oxadiazole, and 2-[2-X-phenyl]-5-phenyl-furane with X = H, F and Cl. The basis set used was 6-31G+(d).

Electronic structure and magnetic anisotropies of antiferromagnetic transition-metal difluorides

NASA Astrophysics Data System (ADS)

Corrêa, Cinthia Antunes; Výborný, Karel

2018-06-01

We compare calculations based on density functional theory (DFT) with available experimental data and analyze the origin of magnetic anisotropies in MnF2, FeF2, CoF2, and NiF2. We confirm that the magnetic anisotropy of MnF2 stems almost completely from the dipolar interaction, while magnetocrystalline anisotropy energy (originating in spin-orbit interaction) plays a dominant role in the other three compounds, and discuss how it depends on the details of band structure. The latter is critically compared to available optical measurements. The case of CoF2, where magnetocrystalline anisotropy energy strongly depends on U (the Hubbard parameter in DFT +U ), is put into contrast with FeF2 where theoretical predictions of magnetic anisotropies are nearly quantitative.

FTIR, FT-Raman spectra and ab initio, DFT vibrational analysis of 2,4-dinitrophenylhydrazine.

PubMed

Sundaraganesan, N; Ayyappan, S; Umamaheswari, H; Joshua, B Dominic

2007-01-01

The FTIR and FT-Raman spectra of 2,4-dinitrophenylhydrazine (2,4-DNPH) has been recorded in the region 4000-400 and 3500-50cm-1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of 2,4-DNPH were obtained by the ab initio and density functional theory (DFT) levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311G(d,p) basis sets. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.

FTIR, FT-Raman spectra and ab initio, DFT vibrational analysis of 2,4-dinitrophenylhydrazine

NASA Astrophysics Data System (ADS)

Sundaraganesan, N.; Ayyappan, S.; Umamaheswari, H.; Dominic Joshua, B.

2007-01-01

The FTIR and FT-Raman spectra of 2,4-dinitrophenylhydrazine (2,4-DNPH) has been recorded in the region 4000-400 and 3500-50 cm -1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of 2,4-DNPH were obtained by the ab initio and density functional theory (DFT) levels of theory with complete relaxation in the potential energy surface using 6-31G(d,p) and 6-311G(d,p) basis sets. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically constructed bar type spectrograms.

N-(4-Nitrobenzoyl)-N'-(1,5-dimethyl-3-oxo-2-phenyl-1H-3(2H)-pyrazolyl)-thiourea hydrate: Synthesis, spectroscopic characterization, X-ray structure and DFT studies

NASA Astrophysics Data System (ADS)

Arslan, N. Burcu; Kazak, Canan; Aydın, Fatma

2012-04-01

The title molecule (C19H17N5O4S·H2O) was synthesized and characterized by IR-NMR spectroscopy, MS and single-crystal X-ray diffraction. The molecular geometry, vibrational frequencies and gauge-independent atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the compound in the ground state have been calculated by using the density functional theory (DFT) method with 6-31G(d) basis set, and compared with the experimental data. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and 1H and 13C NMR chemical shift values show good agreement with experimental data. To determine conformational flexibility, the molecular energy profile of the title compound was obtained with respect to the selected torsion angle, which was varied from -180° to +180° in steps of 10°. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis and thermodynamic properties of the compound were investigated by theoretical calculations.

Molecular modeling the microstructure and phase behavior of bulk and inhomogeneous complex fluids

NASA Astrophysics Data System (ADS)

Bymaster, Adam

Accurate prediction of the thermodynamics and microstructure of complex fluids is contingent upon a model's ability to capture the molecular architecture and the specific intermolecular and intramolecular interactions that govern fluid behavior. This dissertation makes key contributions to improving the understanding and molecular modeling of complex bulk and inhomogeneous fluids, with an emphasis on associating and macromolecular molecules (water, hydrocarbons, polymers, surfactants, and colloids). Such developments apply broadly to fields ranging from biology and medicine, to high performance soft materials and energy. In the bulk, the perturbed-chain statistical associating fluid theory (PC-SAFT), an equation of state based on Wertheim's thermodynamic perturbation theory (TPT1), is extended to include a crossover correction that significantly improves the predicted phase behavior in the critical region. In addition, PC-SAFT is used to investigate the vapor-liquid equilibrium of sour gas mixtures, to improve the understanding of mercaptan/sulfide removal via gas treating. For inhomogeneous fluids, a density functional theory (DFT) based on TPT1 is extended to problems that exhibit radially symmetric inhomogeneities. First, the influence of model solutes on the structure and interfacial properties of water are investigated. The DFT successfully describes the hydrophobic phenomena on microscopic and macroscopic length scales, capturing structural changes as a function of solute size and temperature. The DFT is used to investigate the structure and effective forces in nonadsorbing polymer-colloid mixtures. A comprehensive study is conducted characterizing the role of polymer concentration and particle/polymer size ratio on the structure, polymer induced depletion forces, and tendency towards colloidal aggregation. The inhomogeneous form of the association functional is used, for the first time, to extend the DFT to associating polymer systems, applicable to any association scheme. Theoretical results elucidate how reversible bonding governs the structure of a fluid near a surface and in confined environments, the molecular connectivity (formation of supramolecules, star polymers, etc.) and the phase behavior of the system. Finally, the DFT is extended to predict the inter- and intramolecular correlation functions of polymeric fluids. A theory capable of providing such local structure is important to understanding how local chemistry, branching, and bond flexibility affect the thermodynamic properties of polymers.

Vibrational and electronic investigations, thermodynamic parameters, HOMO and LUMO analysis on Lornoxicam by density functional theory

NASA Astrophysics Data System (ADS)

Suhasini, M.; Sailatha, E.; Gunasekaran, S.; Ramkumaar, G. R.

2015-11-01

The Fourier transform infrared (FT-IR) and FT-Raman spectra of Lornoxicam were recorded in the region 4000-450 cm-1 and 4000-50 cm-1 respectively. Density functional theory (DFT) has been used to calculate the optimized geometrical parameters, atomic charges, and vibrational wavenumbers and intensity of the vibrational bands. The computed vibrational wave numbers were compared with the FT-IR and FT-Raman experimental data. The computational calculations at DFT/B3LYP level with 6-31G(d,p) and 6-31++G(d,p) basis sets. The complete vibrational assignments were performed on the basis of the potential energy distribution (PED) of the Vibrational modes calculated using Vibrational Energy Distribution Analysis (VEDA 4) program. The oscillator's strength calculated by TD-DFT and Lornoxicam is approach complement with the experimental findings. The NMR chemical shifts 13C and 1H were recorded and calculated using the gauge independent atomic orbital (GIAO) method. The Natural charges and intermolecular contacts have been interpreted using Natural Bond orbital (NBO) analysis and the HOMO-LUMO energy gap has been calculated. The thermodynamic properties like Entropy, Enthalpy, Specific heat capacity and zero vibrational energy have been calculated. Besides, molecular electrostatic potential (MEP) was investigated using theoretical calculations.

Interpretation of IR and Raman spectra of dopamine neurotransmitter and effect of hydrogen bond in HCl

NASA Astrophysics Data System (ADS)

Yadav, T.; Mukherjee, V.

2018-05-01

The potential energy scanning with respect to the different dihedral angles were performed to search possible numbers of dopamine (neutral) conformers and further, fifteen conformers of dopamine were identified on the basis of energy minima. Vibrational frequencies were calculated for all the conformers of dopamine. Density functional theory was employed to carry out all the computations. The exchange correlation functional B3LYP and the basis set 6-31++G(d,p) were included in DFT calculation. The FTIR and FT-Raman spectra of dopamine hydrochloride were also recorded in the spectral region 400-4000 cm-1 and 50-4000 cm-1 respectively. The normal coordinate analysis was also performed to scale DFT calculated force constants and to calculate potential energy distributions. The detailed vibrational spectral analysis and the assignments of the bands, done on the best-fit basis comparison of the experimentally obtained and theoretically calculated IR and Raman spectra, match quite well indicating DFT calculations as very accurate source of normal mode assignments. The interaction of the most stable conformer of dopamine with HCl was also studied to know the effect of hydrogen bond on its geometry and dynamics. The stability of the dopamine in isolated and protonated forms arising from hyperconjugative interactions was also analyzed by natural bond orbital analysis.

Experimental and theoretical investigation on the molecular structure, spectroscopic and electric properties of 2,4-dinitrodiphenylamine, 2-nitro-4-(trifluoromethyl)aniline and 4-bromo-2-nitroaniline

NASA Astrophysics Data System (ADS)

Hernández-Paredes, Javier; Hernández-Negrete, Ofelia; Carrillo-Torres, Roberto C.; Sánchez-Zeferino, Raúl; Duarte-Moller, Alberto; Alvarez-Ramos, Mario E.

2015-10-01

2,4-Dinitrodiphenylamine (I), 2-nitro-4-(trifluoromethyl)aniline (II) and 4-bromo-2-nitroaniline (III) have been investigated by DFT and experimental FTIR, Raman and UV-Vis spectroscopies. The gas-phase molecular geometries were consistent with similar compounds already reported in the literature. From the vibrational analysis, the main functional groups were identified and their absorption bands were assigned. Some differences were found between the calculated and the experimental UV-Vis spectra. These differences were analyzed and explained in terms of the TD-DFT/B3LYP limitations, which were mainly attributed to charge-transfer (CT) effects. These findings were in agreement with previous works, which reported that TD-DFT/B3LYP calculations diverge from experimental results when the electronic transitions involve CT. Despite this, TD-DFT/B3LYP calculations provided satisfactory results and a detailed description of the electronic transitions involved in the absorption bands of the UV-Vis spectra. In terms of the NLO properties, it was found that compound (I) is a good candidate for NLO applications and deserves further study due to its good β values. However, the β values for compounds (II) and (III) were negatively affected compared to those found on o-nitroaniline.

Electronic properties of doped and defective NiO: A quantum Monte Carlo study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Hyeondeok; Luo, Ye; Ganesh, Panchapakesan

NiO is a canonical Mott (or charge-transfer) insulator and as such is notoriously difficult to describe using density functional theory (DFT) based electronic structure methods. Doped Mott insulators such as NiO are of interest for various applications but rigorous theoretical descriptions are lacking. Here, we use quantum Monte Carlo methods, which very accurately include electron-electron interactions, to examine energetics, charge- and spin-structures of NiO with various point defects, such as vacancies or substitutional doping with potassium. The formation energy of a potassium dopant is significantly lower than for a Ni vacancy, making potassium an attractive monovalent dopant for NiO. Wemore » compare our results with DFT results that include an on-site Hubbard U (DFT+U) to account for correlations and find relatively large discrepancies for defect formation energies as well as for charge and spin redistributions in the presence of point defects. Finally, it is unlikely that single-parameter fixes of DFT may be able to obtain accurate accounts of anything but a single parameter, e.g., band gap; responses that, maybe in addition to the band gap, depend in subtle and complex ways on ground state properties, such as charge and spin densities, are likely to contain quantitative and qualitative errors.« less

Electronic properties of doped and defective NiO: A quantum Monte Carlo study

DOE PAGES

Shin, Hyeondeok; Luo, Ye; Ganesh, Panchapakesan; ...

2017-12-28

NiO is a canonical Mott (or charge-transfer) insulator and as such is notoriously difficult to describe using density functional theory (DFT) based electronic structure methods. Doped Mott insulators such as NiO are of interest for various applications but rigorous theoretical descriptions are lacking. Here, we use quantum Monte Carlo methods, which very accurately include electron-electron interactions, to examine energetics, charge- and spin-structures of NiO with various point defects, such as vacancies or substitutional doping with potassium. The formation energy of a potassium dopant is significantly lower than for a Ni vacancy, making potassium an attractive monovalent dopant for NiO. Wemore » compare our results with DFT results that include an on-site Hubbard U (DFT+U) to account for correlations and find relatively large discrepancies for defect formation energies as well as for charge and spin redistributions in the presence of point defects. Finally, it is unlikely that single-parameter fixes of DFT may be able to obtain accurate accounts of anything but a single parameter, e.g., band gap; responses that, maybe in addition to the band gap, depend in subtle and complex ways on ground state properties, such as charge and spin densities, are likely to contain quantitative and qualitative errors.« less

Modelling Catalyst Surfaces Using DFT Cluster Calculations

PubMed Central

Czekaj, Izabela; Wambach, Jörg; Kröcher, Oliver

2009-01-01

We review our recent theoretical DFT cluster studies of a variety of industrially relevant catalysts such as TiO2, γ-Al2O3, V2O5-WO3-TiO2 and Ni/Al2O3. Aspects of the metal oxide surface structure and the stability and structure of metal clusters on the support are discussed as well as the reactivity of surfaces, including their behaviour upon poisoning. It is exemplarily demonstrated how such theoretical considerations can be combined with DRIFT and XPS results from experimental studies. PMID:20057947

Structural, electronic and optical properties of monoclinic Na{sub 2}Ti{sub 3}O{sub 7} from density functional theory calculations: A comparison with XRD and optical absorption measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Araújo-Filho, Adailton A.; Silva, Fábio L.R.; Righi, Ariete

Powder samples of bulk monoclinic sodium trititanate Na{sub 2}Ti{sub 3}O{sub 7} were prepared carefully by solid state reaction, and its monoclinic P2{sub 1}/m crystal structure and morphology were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM), respectively. Moreover, the sodium trititanate main energy band gap was estimated as E{sub g}=3.51±0.01 eV employing UV–Vis spectroscopy, which is smaller than the measured 3.70 eV energy gap published previously by other authors. Aiming to achieve a better understanding of the experimental data, density functional theory (DFT) computations were performed within the local density and generalized gradient approximations (LDA and GGA,more » respectively) taking into account dispersion effects through the scheme of Tkatchenko and Scheffler (GGA+TS). Optimal lattice parameters, with deviations relative to measurements Δa=−0.06 Å, Δb=0.02 Å, and Δc=−0.09 Å, were obtained at the GGA level, which was then used to simulate the sodium trititanate electronic and optical properties. Indirect band transitions have led to a theoretical gap energy value of about 3.25 eV. Our results, however, differ from pioneer DFT results with respect to the specific Brillouin zone vectors for which the indirect transition with smallest energy value occurs. Effective masses for electrons and holes were also estimated along a set of directions in reciprocal space. Lastly, our calculations revealed a relatively large degree of optical isotropy for the Na{sub 2}Ti{sub 3}O{sub 7} optical absorption and complex dielectric function. - Graphical abstract: Monoclinic sodium trititanate Na2Ti3O7 was characterized by experiment and dispersion-corrected DFT calculations. An indirect gap of 3.5 eV is predicted, with heavy electrons and anisotropic holes ruling its conductivity. - Highlights: • Monoclinic Na2Ti3O7 was characterized by experiment (XRD, SEM, UV–Vis spectroscopy). • DFT GGA+TS optimized geometry and optoelectronic properties were obtained. • An experimental (theoretical) indirect gap of 3.5 (3.25) eV is predicted. • Heavy electrons and anisotropic holes rule the conductivity. • Ti-O bond lengths and charge states probably cause oxygen reactivity variations.« less

Experimental and theoretical debate on efficient second harmonic generation in Bis (Cinnamic acid): Hexamine cocrystal

NASA Astrophysics Data System (ADS)

Vijayalakshmi, S.; Kalyanaraman, S.; Ravindran, T. R.

2014-02-01

Second harmonic generation (SHG) in Bis (Cinnamic acid): Hexamine cocrystal was extensively analyzed through charge transfer (CT). The CT interactions through hydrogen bonding were well established with the aid of vibrational analysis and Natural Bond Orbital (NBO) analysis. The retentivity of coplanar nature of the cinnamic acid in the cocrystal was confirmed through UV-Visible spectroscopy and supported by Raman studies. Structural analysis indicated the quinoidal character of the given material presenting a high SHG efficiency. The first order hyperpolarizability value was calculated theoretically by density functional theory (DFT) and Hartree-Fock (HF) methods in support for the large value of SHG.

A vibrational study of inulin by means of experimental and theoretical methods

NASA Astrophysics Data System (ADS)

Balan, C.; Chis, M. I.; Rachisan, A. L.; Baia, M.

2018-07-01

Inulin, a natural polymer formed by several units of fructose and just one unit of glucose, is found in different plants or directly in some fruits or vegetables. Due to its structure it has been used in many applications from medicine, pharmacology or food industry. In spite of this, a complete vibrational analysis of the molecule is missing in the literature. Moreover, there are contradictory results regarding the assignment of certain vibrational modes. Therefore, the aim of this study was to obtain a comprehensive vibrational investigation of inulin by means of experimental (FT-IR and Raman spectroscopy) and theoretical (density functional theory -DFT simulations) methods.

Stability and spatial arrangement of the 2,4-dichlorophenoxyacetic acid and β-cyclodextrin inclusion compound: A theoretical study

NASA Astrophysics Data System (ADS)

Pereira, Robson A.; Anconi, Cleber P. A.; Nascimento, Clebio S.; De Almeida, Wagner B.; Dos Santos, Hélio F.

2015-07-01

The present letter reports results from a comprehensive theoretical analysis of the inclusion process involving 2,4-dichlorophenoxyacetic acid (2,4-D) and β-cyclodextrin (β-CD) for which the experimental data of formation is available. Spatial arrangement and stabilization energies were evaluated in gas phase and aqueous solution through density functional theory (DFT) and through the use of SMD implicit solvation approach. The discussed methodology was applied to predict the stability and identify the most favorable form (deprotonated or neutral) as well as the most probable spatial arrangement of the studied inclusion compound.

FTIR, FT-RAMAN, NMR, spectra, normal co-ordinate analysis, NBO, NLO and DFT calculation of N,N-diethyl-4-methylpiperazine-1-carboxamide molecule.

PubMed

Muthu, S; Elamurugu Porchelvi, E

2013-11-01

The Fourier Transform Infrared (FT-IR) and FT-Raman of N,N-diethyl-4-methylpiperazine-1-carboxamide (NND4MC) have been recorded and analyzed. The structure of the compound was optimized and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G(d,p) and 6-311G(d,p) basis sets. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The theoretically predicted FT-IR and FT-Raman spectra of the title molecule have been constructed. The detailed interpretation of the vibrational spectra has been carried out with aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology. Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the σ(*) and π(*) antibonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. The electronic dipole moment (μD) and the first hyperpolarizability (βtot) values of the investigated molecule were computed using Density Functional Theory (DFT/B3LYP) with 6-31G(d,p) and 6-311G(d,p) basis sets. The calculated results also show that the NND4MC molecule may have microscopy nonlinear optical (NLO) behavior with non zero values. Mulliken atomic charges of NND4MC were calculated. The (13)C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. The UV-Vis spectrum of the compound was recorded. The theoretical electronic absorption spectra have been calculated by using CIS, TD-DFT methods. A study on the electronic properties, such as HOMO and LUMO energies, molecular electrostatic potential (MEP) were also performed. Copyright © 2013 Elsevier B.V. All rights reserved.

DFT study of the effect of substituents on the absorption and emission spectra of Indigo

PubMed Central

2012-01-01

Background Theoretical analyses of the indigo dye molecule and its derivatives with Chlorine (Cl), Sulfur (S), Selenium (Se) and Bromine (Br) substituents, as well as an analysis of the Hemi-Indigo molecule, were performed using the Gaussian 03 software package. Results Calculations were performed based on the framework of density functional theory (DFT) with the Becke 3- parameter-Lee-Yang-Parr (B3LYP) functional, where the 6-31 G(d,p) basis set was employed. The configuration interaction singles (CIS) method with the same basis set was employed for the analysis of excited states and for the acquisition of the emission spectra. Conclusions The presented absorption and emission spectra were affected by the substitution position. When a hydrogen atom of the molecule was substituted by Cl or Br, practically no change in the absorbed and emitted energies relative to those of the indigo molecule were observed; however, when N was substituted by S or Se, the absorbed and emitted energies increased. PMID:22809100

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, X. G.; Ning, C. G.; Zhang, S. F.

The measurements of electron density distributions and binding-energy spectrum of the complete valence shell of cyclopentene (C{sub 5}H{sub 8}) using a binary (e,2e) electron momentum spectrometer are reported. The experimental momentum profiles of the valence orbitals are compared with the theoretical distributions calculated using Hartree-Fock and density-functional-theory (DFT) methods with various basis sets. The agreement between theory and experiment for the shape and intensity of the orbital electron momentum distributions is generally good. The DFT calculations employing B3LYP hybrid functional with a saturated and diffuse AUG-CC-PVTZ basis set provide the better descriptions of the experimental data. Some ''turn up'' effectsmore » in the low momentum region of the measured (e,2e) cross section compared with the calculations of 3a{sup ''}, 2a{sup ''}, and 3a{sup '} orbitals could be mainly attributed to distorted-wave effects. The pole strengths of the main ionization peaks from the orbitals in the inner valence are estimated.« less

Electronic-structure and quantum dynamical study of the photochromism of the aromatic Schiff base salicylideneaniline

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel

2008-12-07

The ultrafast proton transfer dynamics of salicylideneaniline has been theoretically analyzed in the ground and first singlet excited electronic states using density functional theory (DFT) and time-dependent DFT calculations, which predict a ({pi},{pi}*) barrierless excited state intramolecular proton transfer (ESIPT). In addition to this, the photochemistry of salicylideneaniline is experimentally known to present fast depopulation processes of the photoexcited species before and after the proton transfer reaction. Such processes are explained by means of conical intersections between the ground and first singlet ({pi},{pi}*) excited electronic states. The electronic energies obtained by the time-dependent density functional theory formalism have been fittedmore » to a monodimensional potential energy surface in order to perform quantum dynamics study of the processes. Our results show that the proton transfer and deactivation of the photoexcited species before the ESIPT processes are completed within 49.6 and 37.7 fs, respectively, which is in remarkable good agreement with experiments.« less

DFT and experimental studies of the structure and vibrational spectra of curcumin

NASA Astrophysics Data System (ADS)

Kolev, Tsonko M.; Velcheva, Evelina A.; Stamboliyska, Bistra A.; Spiteller, Michael

The potential energy surface of curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] was explored with the DFT correlation functional B3LYP method using 6-311G* basis. The single-point calculations were performed at levels up to B3LYP/6-311++G**//B3LYP/6-311G*. All isomers were located and relative energies determined. According to the calculation the planar enol form is more stable than the nonplanar diketo form. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. In addition, harmonic vibrational frequencies of the molecule were evaluated theoretically using B3LYP density functional methods. The computed vibrational frequencies were used to determine the types of molecular motions associated with each of the experimental bands observed. Our vibrational data show that in both the solid state and in all studied solutions curcumin exists in the enol form.

Molecular structure, FT-IR, FT-Raman, NMR studies and first order molecular hyperpolarizabilities by the DFT method of mirtazapine and its comparison with mianserin

NASA Astrophysics Data System (ADS)

Sagdinc, Seda G.; Sahinturk, Ayse Erbay

2013-03-01

Mirtazapine (±)-1,2,3,4,10,14b-hexahydro-2-methylpyrazino(2,1-a)pyrido(2,3-c)(2)benzazepine is a compound with antidepressant therapeutic effects. It is the 6-aza derivative of the tetracyclic antidepressant mianserin (±)-2-methyl-1,2,3,4,10,14b-hexahydrodibenzo[c,f]pyrazino[1,2-a]azepine. The FT-IR and FT-Raman spectra of mirtazapine have been recorded in 4000-400 cm-1 and 3500-10 cm-1, respectively. The optimized geometry, energies, nonlinear optical properties, vibrational frequencies, 13C, 1H and 15N NMR chemical shift values of mirtazapine have been determined using the density functional theory (DFT/B3LYP) method. A comparison of the experimental and theoretical results of mirtazapine indicates that the density-functional B3LYP method is able to provide satisfactory results for predicting vibrational and NMR properties. The experimental and calculated results for mirtazapine have also been compared with mianserin.

Effect of phosphorus on the electronic and optical properties of naphthoxaphospholes: theoretical investigation

NASA Astrophysics Data System (ADS)

Moon, Jiwon; Kim, Minbi; Lim, Jeong Sik; Kim, Joonghan

2018-06-01

Density functional theory (DFT) and time-dependent DFT calculations were performed to elucidate the electronic and optical properties of 2-R-naphthol[2,3-d]oxaphospholes (R-NOPs). On the basis of the calculated results, the poor π overlap between the 3pz orbital of P atom and the 2pz orbitals of other atoms and increasing polarity of P atom result in a reduced energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. When these two effects are considered simultaneously, the absorption energies obtained for the S1 state can be below 3.00 eV according to replace the P atom of oxaphosphole ring by As atom (increasing the poor π overlap) and change the functional groups (increasing polarity). The origin of these two effects is the inherent size of the 3p orbital of P atom. The role of P atom in the control of the electronic and optical properties of R-NOPs is clearly elucidated.

First-Principles Study of Electronic Structure, Mechanical, and Thermoelectric Properties of Ternary Palladates CdPd3O4 and TlPd3O4

NASA Astrophysics Data System (ADS)

Khan, Amin; Ali, Zahid; Khan, Imad; Ahmad, Iftikhar

2018-03-01

Ternary palladates CdPd3O4 and TlPd3O4 have been studied theoretically using the generalized gradient approximation (GGA), modified Becke-Johnson, and spin-orbit coupling (GGA-SOC) exchange-correlation functionals in the density functional theory (DFT) framework. From the calculated ground-state properties, it is found that SOC effects are dominant in these palladates. Mechanical properties reveal that both compounds are ductile in nature. The electronic band structures show that CdPd3O4 is metallic, whereas TlPd3O4 is an indirect-bandgap semiconductor with energy gap of 1.1 eV. The optical properties show that TlPd3O4 is a good dielectric material. The dense electronic states, narrow-gap semiconductor nature, and Seebeck coefficient of TlPd3O4 suggest that it could be used as a good thermoelectric material. The magnetic susceptibility calculated by post-DFT treatment confirmed the paramagnetic behavior of these compounds.

Sulphonamides as corrosion inhibitor: Experimental and DFT studies

NASA Astrophysics Data System (ADS)

Obayes, Hasan R.; Al-Amiery, Ahmed A.; Alwan, Ghadah H.; Abdullah, Thamer Adnan; Kadhum, Abdul Amir H.; Mohamad, Abu Bakar

2017-06-01

Inhibitors are synthetic and natural molecules have various functional groups like double or triple bonds and heteroatoms; N, O or S, which permit adsorption onto the MS (metal surface). These inhibitors have the ability to adsorb onto the MS and block the active site that was reducing the corrosion rate. Inhibition efficiencies of the investigated compounds: Sulfacetamide (SAM), Sulfamerazine (SMR), Sulfapyridine (SPY) and Sulfathiazole (STI), as inhibitors in corrosive solution were evaluated based on weight loss technique. Nitro and Amino groups were chosen for the study of the substituted reaction of four corrosion inhibitor compounds: SAM, SMR, SPY and STI, theoretically utilizing the thickness capacities hypothesis DFT (density functions theory) method with the level [rB3LYP/6-311G(d,p)]. Our research demonstrated that the nitration of studied molecules lead to a diminishing in inhibition efficiencies, group lead to an increase in inhibition efficiency. Compared with corrosion inhibitor molecules these results gave a significant improvement in inhibition efficiency for corrosion inhibitor molecules.

Density functional perturbational orbital theory of spin polarization in electronic systems. II. Transition metal dimer complexes.

PubMed

Seo, Dong-Kyun

2007-11-14

We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.

Is the Bethe–Salpeter Formalism Accurate for Excitation Energies? Comparisons with TD-DFT, CASPT2, and EOM-CCSD

PubMed Central

2017-01-01

Developing ab initio approaches able to provide accurate excited-state energies at a reasonable computational cost is one of the biggest challenges in theoretical chemistry. In that framework, the Bethe–Salpeter equation approach, combined with the GW exchange-correlation self-energy, which maintains the same scaling with system size as TD-DFT, has recently been the focus of a rapidly increasing number of applications in molecular chemistry. Using a recently proposed set encompassing excitation energies of many kinds [J. Phys. Chem. Lett.2016, 7, 586–591], we investigate here the performances of BSE/GW. We compare these results to CASPT2, EOM-CCSD, and TD-DFT data and show that BSE/GW provides an accuracy comparable to the two wave function methods. It is particularly remarkable that the BSE/GW is equally efficient for valence, Rydberg, and charge-transfer excitations. In contrast, it provides a poor description of triplet excited states, for which EOM-CCSD and CASPT2 clearly outperform BSE/GW. This contribution therefore supports the use of the Bethe–Salpeter approach for spin-conserving transitions. PMID:28301726

U(v) in metal uranates: A combined experimental and theoretical study of MgUO 4, CrUO 4, and FeUO 4

DOE PAGES

Guo, Xiaofeng; Tiferet, Eitan; Qi, Liang; ...

2016-01-01

Although pentavalent uranium can exist in aqueous solution, its presence in the solid state is uncommon. Metal monouranates, MgUO 4, CrUO 4 and FeUO 4 were synthesized for detailed structural and energetic investigations. Structural characteristics of these uranates used powder X-ray diffraction, synchrotron X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe-Mossbauer spectroscopy. Enthalpies of formation were measured by high temperature oxide melt solution calorimetry. Density functional theory (DFT) calculations provided both structural and energetic information. The measured structural and thermodynamic properties show good consistency with those predicted from DFT. The presence of U 5+ has been solidly confirmed in CrUOmore » 4 and FeUO 4, which are thermodynamically stable compounds, and the origin and stability of U 5+ in the system was elaborated by DFT. Lastly, the structural and thermodynamic behaviour of U 5+ elucidated in this work is relevant to fundamental actinide redox chemistry and to applications in the nuclear industry and radioactive waste disposal.« less

Revealing electronic open quantum systems with subsystem TDDFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krishtal, Alisa, E-mail: alisa.krishtal@rutgers.edu; Pavanello, Michele, E-mail: m.pavanello@rutgers.edu

2016-03-28

Open quantum systems (OQSs) are perhaps the most realistic systems one can approach through simulations. In recent years, describing OQSs with Density Functional Theory (DFT) has been a prominent avenue of research with most approaches based on a density matrix partitioning in conjunction with an ad-hoc description of system-bath interactions. We propose a different theoretical approach to OQSs based on partitioning of the electron density. Employing the machinery of subsystem DFT (and its time-dependent extension), we provide a novel way of isolating and analyzing the various terms contributing to the coupling between the system and the surrounding bath. To illustratemore » the theory, we provide numerical simulations on a toy system (a molecular dimer) and on a condensed phase system (solvated excimer). The simulations show that non-Markovian dynamics in the electronic system-bath interactions are important in chemical applications. For instance, we show that the superexchange mechanism of transport in donor-bridge-acceptor systems is a non-Markovian interaction between the donor-acceptor (OQS) with the bridge (bath) which is fully characterized by real-time subsystem time-dependent DFT.« less

Revealing electronic open quantum systems with subsystem TDDFT.

PubMed

Krishtal, Alisa; Pavanello, Michele

2016-03-28

Open quantum systems (OQSs) are perhaps the most realistic systems one can approach through simulations. In recent years, describing OQSs with Density Functional Theory (DFT) has been a prominent avenue of research with most approaches based on a density matrix partitioning in conjunction with an ad-hoc description of system-bath interactions. We propose a different theoretical approach to OQSs based on partitioning of the electron density. Employing the machinery of subsystem DFT (and its time-dependent extension), we provide a novel way of isolating and analyzing the various terms contributing to the coupling between the system and the surrounding bath. To illustrate the theory, we provide numerical simulations on a toy system (a molecular dimer) and on a condensed phase system (solvated excimer). The simulations show that non-Markovian dynamics in the electronic system-bath interactions are important in chemical applications. For instance, we show that the superexchange mechanism of transport in donor-bridge-acceptor systems is a non-Markovian interaction between the donor-acceptor (OQS) with the bridge (bath) which is fully characterized by real-time subsystem time-dependent DFT.

Electronic structure of YbB 6 : Is it a topological insulator or not?

DOE PAGES

Kang, Chang -Jong; Denlinger, J. D.; Allen, J. W.; ...

2016-03-17

Here, to finally resolve the controversial issue of whether or not the electronic structure of YbB6 is nontrivially topological, we have made a combined study using angle-resolved photoemission spectroscopy (ARPES) of the nonpolar (110) surface and density functional theory (DFT). The flat-band conditions of the (110) ARPES avoid the strong band bending effects of the polar (001) surface and definitively show that YbB 6 has a topologically trivial B 2p–Yb 5d semiconductor band gap of ~0.3 eV. Accurate determination of the low energy band topology in DFT requires the use of a modified Becke-Johnson exchange potential incorporating spin-orbit coupling andmore » an on-site Yb 4f Coulomb interaction U as large as 7 eV. The DFT result, confirmed by a more precise GW band calculation, is similar to that of a small gap non-Kondo nontopological semiconductor. Additionally, the pressure-dependent electronic structure of YbB 6 is investigated theoretically and found to transform into a p–d overlap semimetal with small Yb mixed valency.« less

Revealing electronic open quantum systems with subsystem TDDFT

NASA Astrophysics Data System (ADS)

Krishtal, Alisa; Pavanello, Michele

2016-03-01

Open quantum systems (OQSs) are perhaps the most realistic systems one can approach through simulations. In recent years, describing OQSs with Density Functional Theory (DFT) has been a prominent avenue of research with most approaches based on a density matrix partitioning in conjunction with an ad-hoc description of system-bath interactions. We propose a different theoretical approach to OQSs based on partitioning of the electron density. Employing the machinery of subsystem DFT (and its time-dependent extension), we provide a novel way of isolating and analyzing the various terms contributing to the coupling between the system and the surrounding bath. To illustrate the theory, we provide numerical simulations on a toy system (a molecular dimer) and on a condensed phase system (solvated excimer). The simulations show that non-Markovian dynamics in the electronic system-bath interactions are important in chemical applications. For instance, we show that the superexchange mechanism of transport in donor-bridge-acceptor systems is a non-Markovian interaction between the donor-acceptor (OQS) with the bridge (bath) which is fully characterized by real-time subsystem time-dependent DFT.

Genetic algorithm based approach to investigate doped metal oxide materials: Application to lanthanide-doped ceria

NASA Astrophysics Data System (ADS)

Hooper, James; Ismail, Arif; Giorgi, Javier B.; Woo, Tom K.

2010-06-01

A genetic algorithm (GA)-inspired method to effectively map out low-energy configurations of doped metal oxide materials is presented. Specialized mating and mutation operations that do not alter the identity of the parent metal oxide have been incorporated to efficiently sample the metal dopant and oxygen vacancy sites. The search algorithms have been tested on lanthanide-doped ceria (L=Sm,Gd,Lu) with various dopant concentrations. Using both classical and first-principles density-functional-theory (DFT) potentials, we have shown the methodology reproduces the results of recent systematic searches of doped ceria at low concentrations (3.2% L2O3 ) and identifies low-energy structures of concentrated samarium-doped ceria (3.8% and 6.6% L2O3 ) which relate to the experimental and theoretical findings published thus far. We introduce a tandem classical/DFT GA algorithm in which an inexpensive classical potential is first used to generate a fit gene pool of structures to enhance the overall efficiency of the computationally demanding DFT-based GA search.

A comparative study of the hydrogen-bonding patterns and prototropism in solid 2-thiocytosine (potential antileukemic agent) and cytosine, as studied by 1H-14N NQDR and QTAIM/ DFT.

PubMed

Latosińska, Jolanta N; Seliger, Janez; Zagar, Veselko; Burchardt, Dorota V

2012-01-01

A potential antileukemic and anticancer agent, 2-thiocytosine (2-TC), has been studied experimentally in the solid state by (1)H-(14)N NMR-NQR double resonance (NQDR) and theoretically by the quantum theory of atoms in molecules (QTAIM)/density functional theory (DFT). Eighteen resonance frequencies on (14)N were detected at 180 K and assigned to particular nitrogen sites (-NH(2), -N=, and -NH-) in 2-thiocytosine. Factors such as the nonequivalence of molecules (connected to the duplication of sites) and possible prototropic tautomerism (capable of modifying the type of site due to proton transfer) were taken into account during frequency assignment. The result of replacing oxygen with sulfur, which leads to changes in the intermolecular interaction pattern and molecular aggregation, is discussed. This study demonstrates the advantages of combining NQDR and DFT to extract detailed information on the H-bonding properties of crystals with complex H-bonding networks. Solid-state properties were found to have a profound impact on the stabilities and reactivities of both compounds.

Understanding cage effects in imidazolium ionic liquids by 129Xe NMR: MD simulations and relativistic DFT calculations.

PubMed

Saielli, Giacomo; Bagno, Alessandro; Castiglione, Franca; Simonutti, Roberto; Mauri, Michele; Mele, Andrea

2014-12-04

(129)Xe NMR has been recently employed to probe the local structure of ionic liquids (ILs). However, no theoretical investigation has been yet reported addressing the problem of the dependence of the chemical shift of xenon on the cage structure of the IL. Therefore, we present here a study of the chemical shift of (129)Xe in two ionic liquids, [bmim][Cl] and [bmim][PF6], by a combination of classical MD simulations and relativistic DFT calculations of the xenon shielding constant. The bulk structure of the two ILs is investigated by means of the radial distribution functions, paying special attention to the local structure, volume, and charge distribution of the cage surrounding the xenon atom. Relativistic DFT calculations, based on the ZORA formalism, on clusters extracted from the trajectory files of the two systems, yield an average relative chemical shift in good agreement with the experimental data. Our results demonstrate the importance of the cage volume and the average charge surrounding the xenon nucleus in the IL cage as the factors determining the effective shielding.

Calculation of exchange coupling constants in triply-bridged dinuclear Cu(II) compounds based on spin-flip constricted variational density functional theory.

PubMed

Seidu, Issaka; Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

2012-03-08

The performance of the second-order spin-flip constricted variational density functional theory (SF-CV(2)-DFT) for the calculation of the exchange coupling constant (J) is assessed by application to a series of triply bridged Cu(II) dinuclear complexes. A comparison of the J values based on SF-CV(2)-DFT with those obtained by the broken symmetry (BS) DFT method and experiment is provided. It is demonstrated that our methodology constitutes a viable alternative to the BS-DFT method. The strong dependence of the calculated exchange coupling constants on the applied functionals is demonstrated. Both SF-CV(2)-DFT and BS-DFT affords the best agreement with experiment for hybrid functionals.

Theoretical Probing of Weak Anion-Cation Interactions in Certain Pyridinium-Based Ionic Liquid Ion Pairs and the Application of Molecular Electrostatic Potential in Their Ionic Crystal Density Determination: A Comparative Study Using Density Functional Approach.

PubMed

Joseph, Aswathy; Thomas, Vibin Ipe; Żyła, Gaweł; Padmanabhan, A S; Mathew, Suresh

2018-01-11

A comprehensive study on the structure, nature of interaction, and properties of six ionic pairs of 1-butylpyridinium and 1-butyl-4-methylpyridinium cations in combination with tetrafluoroborate (BF 4 - ), chloride (Cl - ), and bromide (Br - ) anions have been carried out using density functional theory (DFT). The anion-cation interaction energy (ΔE int ), thermochemistry values, theoretical band gap, molecular orbital energy order, DFT-based chemical activity descriptors [chemical potential (μ), chemical hardness (η), and electrophilicity index (ω)], and distribution of density of states (DOS) of these ion pairs were investigated. The ascendancy of the -CH 3 substituent at the fourth position of the 1-butylpyridinium cation ring on the values of ΔE int , theoretical band gap and chemical activity descriptors was evaluated. The ΔE int values were negative for all six ion pairs and were highest for Cl - containing ion pairs. The theoretical band gap value after -CH 3 substitution increased from 3.78 to 3.96 eV (for Cl - ) and from 2.74 to 2.88 eV (for Br - ) and decreased from 4.9 to 4.89 eV (for BF 4 - ). Ion pairs of BF 4 - were more susceptible to charge transfer processes as inferred from their significantly high η values and comparatively small difference in ω value after -CH 3 substitution. The change in η and μ values due to the -CH 3 substituent is negligibly small in all cases except for the ion pairs of Cl - . Critical-point (CP) analyses were carried out to investigate the AIM topological parameters at the interionic bond critical points (BCPs). The RDG isosurface analysis indicated that the anion-cation interaction was dominated by strong H cat ···X ani and C cat ···X ani interactions in ion pairs of Cl - and Br - whereas a weak van der Waal's effect dominated in ion pairs of BF 4 - . The molecular electrostatic potential (MESP)-based parameter ΔΔV min measuring the anion-cation interaction strength showed a good linear correlation with ΔE int for all 1-butylpyridinium ion pairs (R 2 = 0.9918). The ionic crystal density values calculated by using DFT-based MESP showed only slight variations from experimentally reported values.

Synthesis, characterization, and DFT studies of a new chiral ionic liquid from (S)-1-phenylethylamine

NASA Astrophysics Data System (ADS)

Cui, Shuya; Wang, Tao; Hu, Xiaoli

2014-12-01

A new chiral ionic liquid was synthesized from (S)-1-phenylethylamine and it was studied by IR, Raman, polarimetry, NMR and X-ray crystal diffraction. Its vibrational spectral bands are precisely ascribed to the studied structure with the aid of DFT theoretical calculations. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from IR and Raman spectra are assigned based on the results of the theoretical calculations by the DFT-B3LYP method at 6-311G(d,p) level. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies. The vibrational modes assignments were performed by using the animation option of GaussView5.0 graphical interface for Gaussian program.

Conformational analysis and global warming potentials of 1,1,1,3,3,3-hexafluoro-2-propanol from absorption spectroscopy

NASA Astrophysics Data System (ADS)

Godin, Paul J.; Le Bris, Karine; Strong, Kimberly

2017-12-01

Absorption cross-sections of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) were derived from Fourier transform infrared spectra recorded from 530 to 3400 cm-1 with a resolution of 0.1 cm-1 over a temperature range of 300-362 K. These results were compared to previously published experimental measurements made at room temperature and to a theoretical spectrum from density functional theory (DFT) calculations. Good agreement is found between the experimentally derived results, DFT calculations, and previously published data. The only temperature dependence observed was in the amplitude of some of the absorption peaks due to the changing ratio of the stable conformations of HFIP. This temperature dependence does not result in a significant trend in integrated band strength as a function of temperature. The average value for integrated band strength is found to be (2.649 ± 0.065)x10-16 cm molecule-1 for HFIP over the spectral range of 595 to 3010 cm-1. Radiative efficiency (RE) and the global warming potential (GWP) for HFIP were also derived. A RE of 0.293 ± 0.059 Wm-2ppbv-1 is derived, which leads to a GWP100 of 188 in the range of 530 to 3000 cm-1. The DFT calculation is linearly adjusted to match the experimental spectrum. Using this adjusted DFT spectrum to expand the range below 530 to 0 cm-1 , increases the RE to 0.317 ± 0.063 Wm-2ppbv-1 and the GWP100 to 203.

Strain-induced insulator-to-metal transition in LaTiO3 within DFT + DMFT

NASA Astrophysics Data System (ADS)

Dymkowski, Krzysztof; Ederer, Claude

2014-04-01

We present results of combined density functional theory plus dynamical mean-field theory (DFT + DMFT) calculations, which show that the Mott insulator LaTiO3 undergoes an insulator-to-metal transition under compressive epitaxial strain of about -2%. This transition is driven by strain-induced changes in the crystal-field splitting between the Ti t2g orbitals, which in turn are intimately related to the collective tilts and rotations of the oxygen octahedra in the orthorhombically distorted Pbnm perovskite structure. An accurate treatment of the underlying crystal structure is therefore crucial for a correct description of the observed metal-insulator transition. Our theoretical results are consistent with recent experimental observations and demonstrate that metallic behavior in heterostructures of otherwise insulating materials can emerge also from mechanisms other than genuine interface effects.

Impact of zeolite-Y framework on the geometry and reactivity of Ru (III) benzimidazole complexes - A DFT study

NASA Astrophysics Data System (ADS)

Selvaraj, Tamilmani; Rajalingam, Renganathan; Balasubramanian, Viswanathan

2018-03-01

A detailed comparative Density Functional Theory (DFT) study is made to understand the structural changes of the guest complex due to steric and electronic interactions with the host framework. In this study, Ru(III) benzimidazole and 2- ethyl Ru(III) benzimidazole complexes encapsulated in a supercage of zeolite Y. The zeolitic framework integrity is not disturbed by the intrusion of the large guest complex. A blue shift in the d-d transition observed in the UV-Visible spectroscopic studies of the zeolite encapsulated complexes and they shows a higher catalytic efficiency. Encapsulation of zeolite matrix makes the metal center more viable to nucleophilic attack and favors the phenol oxidation reaction. Based on the theoretical calculations, transition states and structures of reaction intermediates involved in the catalytic cycles are derived.

Ortho and para hydrogen dimers on G/SiC(0001): combined STM and DFT study.

PubMed

Merino, P; Švec, M; Martínez, J I; Mutombo, P; Gonzalez, C; Martín-Gago, J A; de Andres, P L; Jelinek, P

2015-01-01

The hydrogen (H) dimer structures formed upon room-temperature H adsorption on single layer graphene (SLG) grown on SiC(0001) are addressed using a combined theoretical-experimental approach. Our study includes density functional theory (DFT) calculations for the full (6√3 × 6√3)R30° unit cell of the SLG/SiC(0001) substrate and atomically resolved scanning tunneling microscopy images determining simultaneously the graphene lattice and the internal structure of the H adsorbates. We show that H atoms normally group in chemisorbed coupled structures of different sizes and orientations. We make an atomic scale determination of the most stable experimental geometries, the small dimers and ellipsoid-shaped features, and we assign them to hydrogen adsorbed in para dimers and ortho dimers configuration, respectively, through comparison with the theory.

Elastic and Photoelastic Properties of M(NO3)2, MO (M = Mg, Ca, Sr, Ba)

NASA Astrophysics Data System (ADS)

Zhuravlev, Yu. N.; Korabel'nikov, D. V.

2017-05-01

The paper deals with ab initio investigations of elastic and photoelastic properties of oxides and nitrates of alkaline-earth metals. In gradient approximation of the density functional theory (DFT), these properties are studied with the use of the linear combination of the atomic orbital technique. DFT calculations are done with the CRYSTAL 14 software package. The paper introduces the elastic and photoelastic constants, anisotropy parameters for single-crystalline phases and the elastic modules, hardness, Poisson ratio for polycrystalline phases. Such parameters as sonic speed, Debye temperature, thermal conductivity, and Gruneisen parameter are estimated herein. For the fist time, mechanical stability, anisotropy of elastic and photoelastic properties and their dependences are investigated ab initio in this paper. Experimental results on elastic and photoelastic properties of oxides and nitrates are in good agreement with theoretical calculations.

Search For a Consistent Mean-Field Treatment of Magnetic Properties of Yittrium-Cobalt-5 Under Moderate Hydrostatic Stress

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benedict, Lorin X.; Aberg, Daniel; Soderlind, Per

2015-10-26

We explore the use of particular variants of DFT + U and DFT + orbital polarization (OP) to calculate the electronic structure and magnetic properties of YCo5 under hydrostatic pressures up to 600 kbar. While the speci c DFT + U (with U= 0.75 eV) and DFT + OP schemes we employ produce magneto-crystalline anisotropy energies for YCo5 in good agreement with experiments performed in ambient conditions, our DFT + U results are shown to greatly overestimate the pressure at which a high-spin to low-spin (HS-LS) transition is known to occur. In contrast, our DFT + OP results predict themore » HS-LS transition to occur at the same stress as DFT, and in better agreement with experiment. This sensitivity suggests that care should be taken when attempting to model magnetic properties with self-interaction and/or correlation corrections to DFT for this and related materials, and highlights the usefulness of moderate pressure as an additional parameter to vary when discriminating between candidate theoretical schemes.« less

Study of transmission function and electronic transport in one dimensional silver nanowire: Ab-initio method using density functional theory (DFT)

NASA Astrophysics Data System (ADS)

Thakur, Anil; Kashyap, Rajinder

2018-05-01

Single nanowire electrode devices have their application in variety of fields which vary from information technology to solar energy. Silver nanowires, made in an aqueous chemical reduction process, can be reacted with gold salt to create bimetallic nanowires. Silver nanowire can be used as electrodes in batteries and have many other applications. In this paper we investigated structural and electronic transport properties of Ag nanowire using density functional theory (DFT) with SIESTA code. Electronic transport properties of Ag nanowire have been studied theoretically. First of all an optimized geometry for Ag nanowire is obtained using DFT calculations, and then the transport relations are obtained using NEGF approach. SIESTA and TranSIESTA simulation codes are used in the calculations respectively. The electrodes are chosen to be the same as the central region where transport is studied, eliminating current quantization effects due to contacts and focusing the electronic transport study to the intrinsic structure of the material. By varying chemical potential in the electrode regions, an I-V curve is traced which is in agreement with the predicted behavior. Bulk properties of Ag are in agreement with experimental values which make the study of electronic and transport properties in silver nanowires interesting because they are promising materials as bridging pieces in nanoelectronics. Transmission coefficient and V-I characteristic of Ag nano wire reveals that silver nanowire can be used as an electrode device.

The spectroscopic (FT-IR, FT-Raman, UV) and first order hyperpolarizability, HOMO and LUMO analysis of 3-aminobenzophenone by density functional method

NASA Astrophysics Data System (ADS)

Karabacak, M.; Kurt, M.; Cinar, M.; Ayyappan, S.; Sudha, S.; Sundaraganesan, N.

In this work, experimental and theoretical study on the molecular structure and the vibrational spectra of 3-aminobenzophenone (3-ABP) is presented. The vibrational frequencies of the title compound were obtained theoretically by DFT/B3LYP calculations employing the standard 6-311++G(d,p) basis set for optimized geometry and were compared with Fourier transform infrared spectrum (FTIR) in the region of 400-4000 cm-1 and with Fourier Transform Raman spectrum in the region of 50-4000 cm-1. Complete vibrational assignments, analysis and correlation of the fundamental modes for the title compound were carried out. The vibrational harmonic frequencies were scaled using scale factor, yielding a good agreement between the experimentally recorded and the theoretically calculated values.

The DFT Calculations of Structures and EPR Parameters for the Dinuclear Paddle-Wheel Copper(II) Complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) as Powder or Single Crystal

NASA Astrophysics Data System (ADS)

Ding, Chang-Chun; Wu, Shao-Yi; Xu, Yong-Qiang; Zhang, Li-Juan; Zhang, Zhi-Hong; Zhu, Qin-Sheng; Wu, Ming-He; Teng, Bao-Hua

2017-10-01

Density functional theory (DFT) calculations of the structures and the Cu2+ g factors (gx, gy and gz ) and hyperfine coupling tensor A (Ax , Ay and Az ) were performed for the paddle-wheel (PW)-type binuclear copper(II) complex {Cu2(μ2-O2CCH3)4}(OCNH2CH3) powder and single crystal. Calculations were carried out with the ORCA software using the functionals BHandHlyp, B3P86 and B3LYP with five different basis sets: 6-311g, 6-311g(d,p), VTZ, def-2 and def2-TZVP. Results were tested by the MPAD analysis to find the most suitable functional and basis sets. The electronic structure and covalency between copper and oxygen were investigated by the electron localisation function and the localised orbital locator as well as the Mayer bond order for the [CuO5] group. The optical spectra were theoretically calculated by the time-dependent DFT module and plotted by the Multiwfn program for the [CuO5] group and reasonably associated with the local structure in the vicinity of the central ion copper. In addition, the interactions between the OCNH2CH3, NH3 and H2O molecules and the uncoordinated PW copper(II) complex were studied, and the corresponding adsorption energies, the frequency shifts with respect to the free molecules and the changes of the Cu-Cu distances were calculated and compared with the relevant systems.

Structural stability and electronic structure of transition metal compound: HfN

NASA Astrophysics Data System (ADS)

Sarwan, Madhu; Shukoor, V. Abdul; Singh, Sadhna

2018-05-01

The structural stability of transition metal nitride (HfN) has been investigated using density functional theory (DFT) with the help of Quantum-espresso codes. Our calculations confirm that the hafnium nitride (HfN) is stable in zinc-blende (B3) and rock-salt (B1) type structure. We have also reported the structural and electronic properties of HfN compound. These structural properties have been compared with experimental and theoretical data available on this compound.

Experimental and Theoretical Vibrational Spectra of Sideridiol Isolated from Sideritis Species

NASA Astrophysics Data System (ADS)

Kilic, Turgut; Sagir, Züleyha Ozer; Carikci, Sema; Azizoğlu, Akın

2017-12-01

Sideridiol ( ent-7α,18β-dihydroxykaur-15-ene) one of the ent-kaurene diterpenoid, is isolated from the genus Sideritis L. belongs to the family of Lamiaceae. The vibrational frequencies of sideridiol in the ground state have been calculated using the Density Functional Theory (DFT) method with the 6-31G( d) and 6 31+G( d, p) basis sets. The calculated vibrational frequencies have been compared with that of obtained experimental IR spectrum.

FT-IR, FT-Raman, UV, NMR spectra and molecular structure investigation of (E)-2-(3-chloropyrazin-2-yl)-1-(3-ethyl-2, 6-diphenyl piperidin-4-ylidene) hydrazine: A combined experimental and theoretical study

NASA Astrophysics Data System (ADS)

Therasa Alphonsa, A.; Loganathan, C.; Athavan Alias Anand, S.; Kabilan, S.

2015-11-01

This work presents the characterization of (E)-2-(3-chloropyrazin-2-yl)-1-(3-ethyl-2, 6-diphenyl piperidin-4-ylidene) hydrazine (HDE) by quantum chemical calculations and spectral techniques. The structure was investigated by FT-IR, FT-Raman, UV-vis and NMR techniques. The geometrical parameters and energies have been obtained from Density functional theory (DFT) B3LYP (6-31G (d, p)) basis set calculations. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. 1H and 13C NMR chemical shifts of the molecule were calculated using Gauge-independent atomic orbital method (GIAO). The electronic properties such as excitation energies, wavelength, HOMO, LUMO energies performed by Time dependent density functional theory (TD-DFT) results complements with the experimental findings. NBO analysis has been performed for analyzing charge delocalization throughout the molecule. The calculation results were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. To provide information about the interactions between human cytochrome protein and the novel compound theoretically, docking studies were carried out using Schrödinger software.

Theoretical studies on the electronic structure and spectroscopic properties of transition metals bis(dipyrrinate)s

NASA Astrophysics Data System (ADS)

Ksenofontov, Alexander A.; Guseva, Galina B.; Antina, Elena V.

2016-10-01

Density functional theory (DFT) and Time-dependent density functional theory (TD- DFT) computations have been used to reveal structural, molecular, electronic and spectral-luminescent parameters and features of several homoleptic transition metals bis(dipyrrine) complexes. The influence of complexing agent and ligand nature on the regularities in geometric, spectral-luminescent properties, kinetic and thermal stability changes in the [M2L2] complexes series were studied. Special attention is paid to the influence of the solvating media (PCM/TD-B3LYP/Def2-SVP) on changing spectral-luminescent properties of d-metals bis(dipyrrinate)s. The interpretation of the dependence between spectral-luminescent properties of the complexes and HOMO-LUMO (highest occupied molecular orbital and lowest unoccupied molecular orbital) energy gap's width was given. It was shown that the regularities in changing the helicates' quantum yield depending on the nature of complexing agent, ligand and solvent properties, obtained from quantum-chemical calculations, are in the agreement with our previously obtained experimental data. Thus, structural and spectral-luminescent characteristics of new [M2L2] luminophors can be evaluated with high reliability, and good forecast prospects for their use as fluorescent dyes for optical devices can be made in terms of the results of theoretical studies (B3LYP/Def2-SVP and TD-B3LYP/Def2-SVP).

Theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis-, and trans-1,2-difluoroethylenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nozirov, Farhod, E-mail: teobaldk@gmail.com, E-mail: farhod.nozirov@gmail.com; Stachów, Michał, E-mail: michal.stachow@gmail.com; Kupka, Teobald, E-mail: teobaldk@gmail.com, E-mail: farhod.nozirov@gmail.com

2014-04-14

A theoretical prediction of nuclear magnetic shieldings and indirect spin-spin coupling constants in 1,1-, cis- and trans-1,2-difluoroethylenes is reported. The results obtained using density functional theory (DFT) combined with large basis sets and gauge-independent atomic orbital calculations were critically compared with experiment and conventional, higher level correlated electronic structure methods. Accurate structural, vibrational, and NMR parameters of difluoroethylenes were obtained using several density functionals combined with dedicated basis sets. B3LYP/6-311++G(3df,2pd) optimized structures of difluoroethylenes closely reproduced experimental geometries and earlier reported benchmark coupled cluster results, while BLYP/6-311++G(3df,2pd) produced accurate harmonic vibrational frequencies. The most accurate vibrations were obtained using B3LYP/6-311++G(3df,2pd)more » with correction for anharmonicity. Becke half and half (BHandH) density functional predicted more accurate {sup 19}F isotropic shieldings and van Voorhis and Scuseria's τ-dependent gradient-corrected correlation functional yielded better carbon shieldings than B3LYP. A surprisingly good performance of Hartree-Fock (HF) method in predicting nuclear shieldings in these molecules was observed. Inclusion of zero-point vibrational correction markedly improved agreement with experiment for nuclear shieldings calculated by HF, MP2, CCSD, and CCSD(T) methods but worsened the DFT results. The threefold improvement in accuracy when predicting {sup 2}J(FF) in 1,1-difluoroethylene for BHandH density functional compared to B3LYP was observed (the deviations from experiment were −46 vs. −115 Hz)« less

Synthesis, characterization, and DFT studies of a new chiral ionic liquid from (S)-1-phenylethylamine.

PubMed

Cui, Shuya; Wang, Tao; Hu, Xiaoli

2014-12-10

A new chiral ionic liquid was synthesized from (S)-1-phenylethylamine and it was studied by IR, Raman, polarimetry, NMR and X-ray crystal diffraction. Its vibrational spectral bands are precisely ascribed to the studied structure with the aid of DFT theoretical calculations. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from IR and Raman spectra are assigned based on the results of the theoretical calculations by the DFT-B3LYP method at 6-311G(d,p) level. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies.The vibrational modes assignments were performed by using the animation option of GaussView5.0 graphical interface for Gaussian program. Copyright © 2014 Elsevier B.V. All rights reserved.

Theoretical investigation on functional monomer and solvent selection for molecular imprinting of tramadol

NASA Astrophysics Data System (ADS)

Fonseca, Matheus C.; Nascimento, Clebio S.; Borges, Keyller B.

2016-02-01

The purpose of this Letter was to study for the first time the interaction process of tramadol (TRM) with distinct functional monomers (FM) in the formation of molecular imprinted polymer (MIP), using density functional theory (DFT) calculations at B3LYP/6-31G(d,p). As result we were able to establish that the best MIP synthesis conditions are obtained with acrylic acid as FM in 1:3 molar ratio and with chloroform as solvent. This condition presented the lowest stabilization energy for the pre-polymerization complexes. Besides, the intermolecular hydrogen bonds found between the template molecule and functional monomers play a primary role to the complex stability.

Optimization of constrained density functional theory

NASA Astrophysics Data System (ADS)

O'Regan, David D.; Teobaldi, Gilberto

2016-07-01

Constrained density functional theory (cDFT) is a versatile electronic structure method that enables ground-state calculations to be performed subject to physical constraints. It thereby broadens their applicability and utility. Automated Lagrange multiplier optimization is necessary for multiple constraints to be applied efficiently in cDFT, for it to be used in tandem with geometry optimization, or with molecular dynamics. In order to facilitate this, we comprehensively develop the connection between cDFT energy derivatives and response functions, providing a rigorous assessment of the uniqueness and character of cDFT stationary points while accounting for electronic interactions and screening. In particular, we provide a nonperturbative proof that stable stationary points of linear density constraints occur only at energy maxima with respect to their Lagrange multipliers. We show that multiple solutions, hysteresis, and energy discontinuities may occur in cDFT. Expressions are derived, in terms of convenient by-products of cDFT optimization, for quantities such as the dielectric function and a condition number quantifying ill definition in multiple constraint cDFT.

Synthesis, spectroscopic and structural characterization of 5-benzoyl-4-phenyl-2-methylthio-1H-pyrimidine with theoretical calculations using density functional theory.

PubMed

Inkaya, Ersin; Dinçer, Muharrem; Sahan, Emine; Yıldırım, Ismail

2013-10-01

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameters (FT-IR, (1)H NMR, (13)C NMR) of 5-benzoyl-4-phenyl-2-methylthio-1H-pyrimidine. The compound crystallizes in the triclinic space group P-1 with Z=2. The molecular geometry was also optimized using density functional theory (DFT/B3LYP) method with the 6-311G(d,p) and 6-311++G(d,p) basis sets in ground state and compared with the experimental data. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential (ESP). Also, non-linear optical properties of the title compound were performed at B3LYP/6-311++G(d,p) level. The theoretical results showed an excellent agreement with the experimental values. Copyright © 2013 Elsevier B.V. All rights reserved.

Synthesis, spectroscopic and structural characterization of 5-benzoyl-4-phenyl-2-methylthio-1H-pyrimidine with theoretical calculations using density functional theory

NASA Astrophysics Data System (ADS)

İnkaya, Ersin; Dinçer, Muharrem; Şahan, Emine; Yıldırım, İsmail

2013-10-01

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameters (FT-IR, 1H NMR, 13C NMR) of 5-benzoyl-4-phenyl-2-methylthio-1H-pyrimidine. The compound crystallizes in the triclinic space group P-1 with Z = 2. The molecular geometry was also optimized using density functional theory (DFT/B3LYP) method with the 6-311G(d,p) and 6-311++G(d,p) basis sets in ground state and compared with the experimental data. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential (ESP). Also, non-linear optical properties of the title compound were performed at B3LYP/6-311++G(d,p) level. The theoretical results showed an excellent agreement with the experimental values.

Conformational effect of dicyclo-hexano-18-crown-6 on isotopic fractionation of zinc: DFT approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boda, A.; Singha Deb, A. K.; Ali, Sk. M.

2014-04-24

Generalized gradient approximated BP86 density functional employing triple zeta valence plus polarization (TZVP) basis set has been used to compute the reduced partition function ratio and isotopic separation factor for zinc isotopes. The isotopic separation factor was found to be in good agreement with the experimental results. The isotopic separation factor was found to depend on the conformation of the crown ether ligand. The trans-trans conformation shows the highest fractionation compared to cis-cis conformer. The present theoretical results can thus be used to plan the isotope separation experiments.

Surface modification of carbon nanotubes using 3-aminopropyltriethoxysilane to improve mechanical properties of nanocomposite based polymer matrix: Experimental and Density functional theory study

NASA Astrophysics Data System (ADS)

Hamed Mashhadzadeh, A.; Fereidoon, Ab.; Ghorbanzadeh Ahangari, M.

2017-10-01

In current study we combined theoretical and experimental studies to evaluate the effect of functionalization and silanization on mechanical behavior of polymer-based/CNT nanocomposites. Epoxy was selected as thermoset polymer, polypropylene and poly vinyl chloride were selected as thermoplastic polymers. The whole procedure is divided to two sections . At first we applied density functional theory (DFT) to analyze the effect of functionalization on equilibrium distance and adsorption energy of unmodified, functionalized by sbnd OH group and silanized epoxy/CNT, PP/CNT and PVC/CNT nanocomposites and the results showed that functionalization increased adsorption energy and reduced the equilibrium distance in all studied nanocomposites and silanization had higher effect comparing to OH functionalizing. Then we prepared experimental samples of all mentioned nanocomposites and tested their tensile and flexural strength properties. The obtained results showed that functionalization increased the studied mechanical properties in all evaluated nanocomposites. Finally we compared the results of experimental and theoretical sections with each other and estimated a suitable agreement between these parts.

Energy level alignment and quantum conductance of functionalized metal-molecule junctions: Density functional theory versus GW calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Chengjun; Markussen, Troels; Thygesen, Kristian S., E-mail: thygesen@fysik.dtu.dk

We study the effect of functional groups (CH{sub 3}*4, OCH{sub 3}, CH{sub 3}, Cl, CN, F*4) on the electronic transport properties of 1,4-benzenediamine molecular junctions using the non-equilibrium Green function method. Exchange and correlation effects are included at various levels of theory, namely density functional theory (DFT), energy level-corrected DFT (DFT+Σ), Hartree-Fock and the many-body GW approximation. All methods reproduce the expected trends for the energy of the frontier orbitals according to the electron donating or withdrawing character of the substituent group. However, only the GW method predicts the correct ordering of the conductance amongst the molecules. The absolute GWmore » (DFT) conductance is within a factor of two (three) of the experimental values. Correcting the DFT orbital energies by a simple physically motivated scissors operator, Σ, can bring the DFT conductances close to experiments, but does not improve on the relative ordering. We ascribe this to a too strong pinning of the molecular energy levels to the metal Fermi level by DFT which suppresses the variation in orbital energy with functional group.« less

DFT analysis and spectral characteristics of Celecoxib a potent COX-2 inhibitor

NASA Astrophysics Data System (ADS)

Vijayakumar, B.; Kannappan, V.; Sathyanarayanamoorthi, V.

2016-10-01

Extensive quantum mechanical studies are carried out on Celecoxib (CXB), a new generation drug to understand the vibrational and electronic spectral characteristics of the molecule. The vibrational frequencies of CXB are computed by HF and B3LYP methods with 6-311++G (d, p) basis set. The theoretical scaled vibrational frequencies have been assigned and they agreed satisfactorily with experimental FT-IR and Raman frequencies. The theoretical maximum wavelength of absorption of CXB are calculated in water and ethanol by TD-DFT method and these values are compared with experimentally determined λmax values. The spectral and Natural bonds orbital (NBO) analysis in conjunction with spectral data established the presence of intra molecular interactions such as mesomeric, hyperconjugative and steric effects in CXB. The electron density at various positions and reactivity descriptors of CXB indicate that the compound functions as a nucleophile and establish that aromatic ring system present in the molecule is the site of drug action. Electronic distribution and HOMO - LUMO energy values of CXB are discussed in terms of intra-molecular interactions. Computed values of Mulliken charges and thermodynamic properties of CXB are reported.

Structural investigation of the cocrystal formed between 5-fluorocytosine and fumaric acid based on vibrational spectroscopic technique

NASA Astrophysics Data System (ADS)

Du, Yong; Cai, Qiang; Xue, Jiadan; Zhang, Qi; Qin, Dan

2017-05-01

The vibrational spectra of 5-fluorocytosine, fumaric acid and their cocrystal were measured using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. Experimental THz results show that the cocrystal has distinct fingerprint spectra in terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.61 and 0.91 THz. These are quite different from corresponding raw starting materials. Raman spectra also show similar results about differences between the cocrystal and corresponding raw starting materials. Density functional theory (DFT) was used to simulate the structure of the possible salt form and the cocrystal form between 5-fluorocytosine and fumaric acid. The theoretical terahertz result shows that the cocrystal form has absorption at 0.62 and 0.87 THz, which is in agreement with the experimental result. The theoretical Raman result also indicates that the cocrystal form has more possibilities than the salt form. So, it is more reasonable that the structure between 5-fluorocytosine and fumaric acid could be the corresponding cocrystal form. The characteristic bands of the cocrystal between 5-fluorocytosine and fumaric acid are also assigned based on the simulation results from the DFT calculation.

Optical conductivity calculation of a k.p model semiconductor GaAs incorporating first-order electron-hole vertex correction

NASA Astrophysics Data System (ADS)

Nurhuda, Maryam; Aziz Majidi, Muhammad

2018-04-01

The role of excitons in semiconducting materials carries potential applications. Experimental results show that excitonic signals also appear in optical absorption spectra of semiconductor system with narrow gap, such as Gallium Arsenide (GaAs). While on the theoretical side, calculation of optical spectra based purely on Density Functional Theory (DFT) without taking electron-hole (e-h) interactions into account does not lead to the appearance of any excitonic signal. Meanwhile, existing DFT-based algorithms that include a full vertex correction through Bethe-Salpeter equation may reveal an excitonic signal, but the algorithm has not provided a way to analyze the excitonic signal further. Motivated to provide a way to isolate the excitonic effect in the optical response theoretically, we develop a method of calculation for the optical conductivity of a narrow band-gap semiconductor GaAs within the 8-band k.p model that includes electron-hole interactions through first-order electron-hole vertex correction. Our calculation confirms that the first-order e-h vertex correction reveals excitonic signal around 1.5 eV (the band gap edge), consistent with the experimental data.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fraccarollo, Alberto; Cantatore, Valentina; Boschetto, Gabriele

A number of 2D layered perovskites A{sub 2}PbI{sub 4} and BPbI{sub 4}, with A and B mono- and divalent ammonium and imidazolium cations, have been modeled with different theoretical methods. The periodic structures have been optimized (both in monoclinic and in triclinic systems, corresponding to eclipsed and staggered arrangements of the inorganic layers) at the DFT level, with hybrid functionals, Gaussian-type orbitals and dispersion energy corrections. With the same methods, the various contributions to the solid stabilization energy have been discussed, separating electrostatic and dispersion energies, organic-organic intralayer interactions and H-bonding effects, when applicable. Then the electronic band gaps havemore » been computed with plane waves, at the DFT level with scalar and full relativistic potentials, and including the correlation energy through the GW approximation. Spin orbit coupling and GW effects have been combined in an additive scheme, validated by comparing the computed gap with well known experimental and theoretical results for a model system. Finally, various contributions to the computed band gaps have been discussed on some of the studied systems, by varying some geometrical parameters and by substituting one cation in another’s place.« less

Experimental and DFT studies on DNA binding and photocleavage of two cationic porphyrins. Effects of the introduction of a carboxyphenyl into pyridinium porphyrin.

PubMed

Zhao, Ping; Xu, Lian-Cai; Huang, Jin-Wang; Liu, Jie; Yu, Han-Cheng; Zheng, Kang-Cheng; Ji, Liang-Nian

2008-12-15

The DNA-binding affinities and DNA photocleavage abilities of cationic porphyrin, 5-(4-carboxyphenyl)-10,15,20-tris(4-methylpyridiniumyl)porphyrin (CTMPyP), and its reference compound meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin (H2TMPyP) have been investigated. The DNA-binding behaviors of the two compounds in NaH2PO4 buffer were compared systematically by using absorption, fluorescence and circular dichroism (CD) spectra, thermal denaturation as well as viscosity measurements. The experimental results show that CTMPyP binds to DNA in an outside binding mode, while H2TMPyP in an intercalative mode. Photocleavage experiments reveal that both two compounds employ 1O2-mediated mechanism in cleaving DNA and H2TMPyP can cleave DNA more efficiently than CTMPyP. Theoretical calculations were carried out with the density functional theory (DFT), and the calculated results indicate that the character and energies of some frontier orbitals of CTMPyP are quite different from those of H2TMPyP. These theoretical results can be used to explain their different DNA-binding modes and affinities to a certain extent.

Probing charge transfer complex states in organic solar cells using photocurrent spectroscopy

NASA Astrophysics Data System (ADS)

Moghe, Dhanashree; Adil, Danish; Kanimozhi, Catherine; Dutta, Gitesh; Patil, Satish; Guha, Suchismita

2013-03-01

Diketopyrrolopyrrole (DPP) containing copolymers-fullerene blends have gained a lot of interest in organic optoelectronics with a great potential in organic photovoltaics (OPVs). The interfacial charge transfer complex (CTC) states formed in donor-acceptor blended OPVs play a major role in the overall efficiency of the device. We investigate the spectral photocurrent characteristics of five DPP based copolymers; two of them being benzothiadiazole and carbazole -based statistical copolymers of DPP. These systems provide a wide range of bandgap energies ranging from ~ 1.4 to 1.7 eV. We use Fourier transform photocurrent spectroscopy (FTPS) and monochromatic photocurrent (PC) to identify the CTC states in these DPP copolymer -fullerene blends. The stability of the CTC state is found to be dependent on the band gap energy difference between the donor copolymer and the acceptor. We support our inferences from theoretical results obtained using density-functional theory (DFT) and time-dependent DFT for two DPP based copolymers The theoretical calculations reveal a higher contribution of the CTC states to the lowest excited state in the phenyl-based DPP monomer, which has a larger bandgap energy compared to the thiophene-based DPP system, in the presence of a fullerene molecule.

Theoretical investigations on molecular structure, vibrational spectra, HOMO, LUMO, NBO analysis and hyperpolarizability calculations of thiophene-2-carbohydrazide.

PubMed

Balachandran, V; Janaki, A; Nataraj, A

2014-01-24

The Fourier-Transform infrared and Fourier-Transform Raman spectra of thiophene-2-carbohydrazide (TCH) was recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1). Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of TCH were carried out by DFT (B3LYP) method with 6-311++G(d,p) as basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. Stability of the molecule arising from hyper conjugative interaction and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV spectrum was measured in different solvent. The energy and oscillator strength are calculated by Time Dependant Density Functional Theory (TD-DFT) results. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The complete assignments were performed on the basis of the potential energy distribution (PED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method. Finally the theoretical FT-IR, FT-Raman, and UV spectra of the title molecule have also been constructed. Copyright © 2013 Elsevier B.V. All rights reserved.

Synthesis, crystal structures and spectroscopic properties of triazine-based hydrazone derivatives; a comparative experimental-theoretical study.

PubMed

Arshad, Muhammad Nadeem; Bibi, Aisha; Mahmood, Tariq; Asiri, Abdullah M; Ayub, Khurshid

2015-04-03

We report here a comparative theoretical and experimental study of four triazine-based hydrazone derivatives. The hydrazones are synthesized by a three step process from commercially available benzil and thiosemicarbazide. The structures of all compounds were determined by using the UV-Vis., FT-IR, NMR (1H and 13C) spectroscopic techniques and finally confirmed unequivocally by single crystal X-ray diffraction analysis. Experimental geometric parameters and spectroscopic properties of the triazine based hydrazones are compared with those obtained from density functional theory (DFT) studies. The model developed here comprises of geometry optimization at B3LYP/6-31G (d, p) level of DFT. Optimized geometric parameters of all four compounds showed excellent correlations with the results obtained from X-ray diffraction studies. The vibrational spectra show nice correlations with the experimental IR spectra. Moreover, the simulated absorption spectra also agree well with experimental results (within 10-20 nm). The molecular electrostatic potential (MEP) mapped over the entire stabilized geometries of the compounds indicated their chemical reactivates. Furthermore, frontier molecular orbital (electronic properties) and first hyperpolarizability (nonlinear optical response) were also computed at the B3LYP/6-31G (d, p) level of theory.

An experimental and theoretical study of molecular structure and vibrational spectra of 2-methylphenyl boronic acid by density functional theory calculations

NASA Astrophysics Data System (ADS)

Hiremath, Sudhir M.; Hiremath, C. S.; Khemalapure, S. S.; Patil, N. R.

2018-05-01

This paper reports the experimental and theoretical study on the structure and vibrations of 2-Methylphenyl boronic acid (2MPBA). The different spectroscopic techniques such as FT-IR (4000-400 cm-1) and FT-Raman (4000-50 cm-1) of the title molecule in the solid phase were recorded. The geometry of the molecule was fully optimized using density functional theory (DFT) (B3LYP) with 6-311++G(d, p) basis set calculations. The vibrational wavenumbers were also corrected with scale factor to take better results for the calculated data. Vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the potential energy distribution (PED) of the vibrational modes obtained from VEDA 4 program. The calculated wavenumbers showed the best agreement with the experimental results. Whereas, it is observed that, the theoretical frequencies are more than the experimental one for O-H stretching vibration modes of the title molecule.

Synthesis, crystal structure, vibrational spectra and theoretical calculations of quantum chemistry of a potential antimicrobial Meldrum's acid derivative

NASA Astrophysics Data System (ADS)

Campelo, M. J. M.; Freire, P. T. C.; Mendes Filho, J.; de Toledo, T. A.; Teixeira, A. M. R.; da Silva, L. E.; Bento, R. R. F.; Faria, J. L. B.; Pizani, P. S.; Gusmão, G. O. M.; Coutinho, H. D. M.; Oliveira, M. T. A.

2017-10-01

A new derivative of Meldrum's acid 5-((5-chloropyridin-2-ylamino)methylene)-2,2-dimethyl-1,3-dioxane-4,6-dione (CYMM) of molecular formula C12H11ClN2O4 was synthesized and structurally characterized using single crystal X-ray diffraction technique. The vibrational properties of the crystal were studied by Fourier Transform infrared (FT-IR), Fourier Transform Raman (FT-Raman) techniques and theoretical calculations of quantum chemistry using Density functional theory (DFT) and Density functional perturbation theory (DFPT). A comparison with experimental spectra allowed the assignment of all the normal modes. The descriptions of the normal modes were carried by means of potential energy distribution (PED). Additionally, analysis of the antimicrobial activity and antibiotic resistance modulatory activity was carried out to evaluate the antibacterial potential of the CYMM.

First-Principles Equation of State and Shock Compression of Warm Dense Aluminum and Hydrocarbons

NASA Astrophysics Data System (ADS)

Driver, Kevin; Soubiran, Francois; Zhang, Shuai; Militzer, Burkhard

2017-10-01

Theoretical studies of warm dense plasmas are a key component of progress in fusion science, defense science, and astrophysics programs. Path integral Monte Carlo (PIMC) and density functional theory molecular dynamics (DFT-MD), two state-of-the-art, first-principles, electronic-structure simulation methods, provide a consistent description of plasmas over a wide range of density and temperature conditions. Here, we combine high-temperature PIMC data with lower-temperature DFT-MD data to compute coherent equations of state (EOS) for aluminum and hydrocarbon plasmas. Subsequently, we derive shock Hugoniot curves from these EOSs and extract the temperature-density evolution of plasma structure and ionization behavior from pair-correlation function analyses. Since PIMC and DFT-MD accurately treat effects of atomic shell structure, we find compression maxima along Hugoniot curves attributed to K-shell and L-shell ionization, which provide a benchmark for widely-used EOS tables, such as SESAME and LEOS, and more efficient models. LLNL-ABS-734424. Funding provided by the DOE (DE-SC0010517) and in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Computational resources provided by Blue Waters (NSF ACI1640776) and NERSC. K. Driver's and S. Zhang's current address is Lawrence Livermore Natl. Lab, Livermore, CA, 94550, USA.

Distribution of dopant ions around poly(3,4-ethylenedioxythiophene) chains: a theoretical study.

PubMed

Casanovas, Jordi; Zanuy, David; Alemán, Carlos

2017-04-12

The effect of counterions and multiple polymer chains on the properties and structure of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with ClO 4 - has been examined using density functional theory (DFT) calculations with periodic boundary conditions (PBCs). Calculations on a one-dimensional periodic model with four explicit polymer repeat units and two ClO 4 - molecules indicate that the latter are separated as much as possible, with the salt structure and band gap obtained from such ClO 4 - distribution being in excellent agreement with those determined experimentally. On the other hand, DFT calculations on periodic models that include two chains indicate that neighboring PEDOT chains are shifted along the molecular axis by a half of the repeat unit length, with dopant ions intercalated between the polymer molecules acting as cement. In order to support these structural features, classical molecular dynamics (MD) simulations have been performed on a multiphasic system consisting of 69 explicit PEDOT chains anchored onto a steel surface, explicit ClO 4 - anions embedded in the polymer matrix, and an acetonitrile phase layer onto the polymer matrix. Analyses of the radial distribution functions indicate that the all-anti conformation, the relative disposition of adjacent PEDOT chains and the distribution of ClO 4 - dopant ions are fully consistent with periodic DFT predictions. The agreement between two such different methodologies allows reinforcing the microscopic understanding of the PEDOT film structure.

Diffusion Monte Carlo calculations of Xenon melting under pressure

NASA Astrophysics Data System (ADS)

Shulenburger, L.; Mattsson, T. R.

2011-03-01

The slope of the melting temperature as a function of pressure yields, via the Clausius-Clapeyron equation, important information regarding the changes in density, energy, and entropy. It is therefore crucial to resolve the long-standing differences in melt lines under pressure between Diamond Anvil Cell data (low/flat melt line) and other methods, including density functional theory (DFT) simulations 1 (high/steep melt line). The disagreement for Ta was recently resolved 2 and although a similar situation exists in the literature on Xe,3 the resolution may be quite different. For example, DFT with its lack of van der Waals forces is a prima facie less credible simulation method for Xe, although excellent agreement has been obtained between calculations of the Hugoniot of Xe and experiments.4 We investigate whether this theoretical shortcoming is significant for the melting transition by applying diffusion Monte Carlo. The energy differences obtained in this way are compared to the DFT results in order to address any systematic errors that may be present near the melting transition. 1 Taioli et al. PRB 75, 214103 (2007); 2 Dewaele et al. PRL 104, 255701 (2010); 3 Belonoshko el al. PRB 74, 054114 (2006); 4 Root et al. PRL 105, 085501 (2010) Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corp. for the US Dep. of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

Noble gas cluster ions

NASA Astrophysics Data System (ADS)

Kaya, Yunus; Kalkan, Yalçin; Veenhof, Rob

2018-02-01

In this work, a reaction mechanism of formation of noble gas (Ng) cluster ions has been theoretically investigated in detail. The kinetic studies of formation of Xe+Xe cluster in Xe, Ar+Ar cluster ions in Ar, and Ne+Ne cluster ions in Ne have been made as theoretically. The optimized structures in the ground state were calculated using the density functional theory (DFT) by the B3LYP method combined with the Stuttgart/Dresden effective core potential basis set (SDD). In addition, we calculated the rate constants of all cluster formations. The results are 1.15 × 10-31, 3.58 × 10-31, 0.23 × 10-31cm6/s, respectively for Neon, Argon, Xenon cluster ions.

Experimental and theoretical investigation on the molecular structure, spectroscopic and electric properties of 2,4-dinitrodiphenylamine, 2-nitro-4-(trifluoromethyl)aniline and 4-bromo-2-nitroaniline.

PubMed

Hernández-Paredes, Javier; Hernández-Negrete, Ofelia; Carrillo-Torres, Roberto C; Sánchez-Zeferino, Raúl; Duarte-Moller, Alberto; Alvarez-Ramos, Mario E

2015-10-05

2,4-Dinitrodiphenylamine (I), 2-nitro-4-(trifluoromethyl)aniline (II) and 4-bromo-2-nitroaniline (III) have been investigated by DFT and experimental FTIR, Raman and UV-Vis spectroscopies. The gas-phase molecular geometries were consistent with similar compounds already reported in the literature. From the vibrational analysis, the main functional groups were identified and their absorption bands were assigned. Some differences were found between the calculated and the experimental UV-Vis spectra. These differences were analyzed and explained in terms of the TD-DFT/B3LYP limitations, which were mainly attributed to charge-transfer (CT) effects. These findings were in agreement with previous works, which reported that TD-DFT/B3LYP calculations diverge from experimental results when the electronic transitions involve CT. Despite this, TD-DFT/B3LYP calculations provided satisfactory results and a detailed description of the electronic transitions involved in the absorption bands of the UV-Vis spectra. In terms of the NLO properties, it was found that compound (I) is a good candidate for NLO applications and deserves further study due to its good β values. However, the β values for compounds (II) and (III) were negatively affected compared to those found on o-nitroaniline. Copyright © 2015 Elsevier B.V. All rights reserved.

Invited Paper - Density functional theory: coverage of dynamic and non-dynamic electron correlation effects

NASA Astrophysics Data System (ADS)

Cremer, Dieter

The electron correlation effects covered by density functional theory (DFT) can be assessed qualitatively by comparing DFT densities ρ(r) with suitable reference densities obtained with wavefunction theory (WFT) methods that cover typical electron correlation effects. The analysis of difference densities ρ(DFT)-ρ(WFT) reveals that LDA and GGA exchange (X) functionals mimic non-dynamic correlation effects in an unspecified way. It is shown that these long range correlation effects are caused by the self-interaction error (SIE) of standard X functionals. Self-interaction corrected (SIC) DFT exchange gives, similar to exact exchange, for the bonding region a delocalized exchange hole, and does not cover any correlation effects. Hence, the exchange SIE is responsible for the fact that DFT densities often resemble MP4 or MP2 densities. The correlation functional changes X-only DFT densities in a manner observed when higher order coupling effects between lower order N-electron correlation effects are included. Hybrid functionals lead to changes in the density similar to those caused by SICDFT, which simply reflects the fact that hybrid functionals have been developed to cover part of the SIE and its long range correlation effects in a balanced manner. In the case of spin-unrestricted DFT (UDFT), non-dynamic electron correlation effects enter the calculation both via the X functional and via the wavefunction, which may cause a double-counting of correlation effects. The use of UDFT in the form of permuted orbital and broken-symmetry DFT (PO-UDFT, BS-UDFT) can lead to reasonable descriptions of multireference systems provided certain conditions are fulfilled. More reliable, however, is a combination of DFT and WFT methods, which makes the routine description of multireference systems possible. The development of such methods implies a separation of dynamic and non-dynamic correlation effects. Strategies for accomplishing this goal are discussed in general and tested in practice for CAS (complete active space)-DFT.

DFT with larger supercells explains the band gap formation in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

NASA Astrophysics Data System (ADS)

Zunger, Alex; Trimarchi, Giancarlo

The existence of large band gaps both in the antiferromagnetic (AFM) and the paramagnetic (PM) phases of the classic Mott insulators MnO, FeO, CoO, and NiO has traditionally been discussed in terms of theoretical methods requiring both (i) simple (often primitive) unit cells and (ii) correlated-electron methodologies. We show that if condition (i) is avoided (by using supercells, such as PM special quasi-random structures, in which chemically identical atoms can have different local environments), then even without condition (ii) one can describe the gaps and moments within a single-determinant DFT band structure approach. In this approach gapping is caused by basic structure, magnetism, and bonding effects underlying DFT, not via dynamic correlation (absent from DFT). As long as correlation is simplistically considered as ``anything that DFT does not get right'', gap formation in the AFM and PM phases is not due to correlation. This result defines the minimal theoretical methods needed to explain gapping and points to the possibility that some transition-metal oxides generally considered to have localized electrons detrimental to transport, could, in fact, rejoin the family of electronic semiconductors, to the benefit of a carrier transport technologies. A. Z. supported by DOE-OS-BES-MSE, Grant DE-FG02-13ER46959.

Noncovalent Organocatalysis Based on Hydrogen Bonding: Elucidation of Reaction Paths by Computational Methods

NASA Astrophysics Data System (ADS)

Etzenbach-Effers, Kerstin; Berkessel, Albrecht

In this article, the functions of hydrogen bonds in organocatalytic reactions are discussed on atomic level by presenting DFT studies of selected examples. Theoretical investigation provides a detailed insight in the mechanism of substrate activation and orientation, and the stabilization of transition states and intermediates by hydrogen bonding (e.g. oxyanion hole). The examples selected comprise stereoselective catalysis by bifunctional thioureas, solvent catalysis by fluorinated alcohols in epoxidation by hydrogen peroxide, and intramolecular cooperative hydrogen bonding in TADDOL-type catalysts.

Theory investigation progress of DMAZ

NASA Astrophysics Data System (ADS)

Xie, Hui; Mu, Xiaogang; Zhang, Yue; Wang, Xuanjun

2017-05-01

The recent progress in the theoretical study of N, N-dimethyl-2-azidoethylamine (DMAZ), a new type of azide fuel, is summarized. Thermodynamic Properties (such as Enthalpy-of-Formation, Enthalpy-of-Vaporization, and Enthalpy-of-Sublimation), conformers, Spectrums, the Henry's constant, ignition delay et al. are studied by Density Functional Theory (DFT). It is proved that DMAZ has good performance with a density impulse 2.499 Ns/m3, and has a good application prospect in replacing the traditional hydrazine propellant methyl-hydrazine (MMH).

Quantum Mechanical Calculations of Vibrational Sum-Frequency-Generation (SFG) Spectra of Cellulose: Dependence of the CH and OH Peak Intensity on the Polarity of Cellulose Chains within the SFG Coherence Domain.

PubMed

Lee, Christopher M; Chen, Xing; Weiss, Philip A; Jensen, Lasse; Kim, Seong H

2017-01-05

Vibrational sum-frequency-generation (SFG) spectroscopy is capable of selectively detecting crystalline biopolymers interspersed in amorphous polymer matrices. However, the spectral interpretation is difficult due to the lack of knowledge on how spatial arrangements of crystalline segments influence SFG spectra features. Here we report time-dependent density functional theory (TD-DFT) calculations of cellulose crystallites in intimate contact with two different polarities: parallel versus antiparallel. TD-DFT calculations reveal that the CH/OH intensity ratio is very sensitive to the polarity of the crystallite packing. Theoretical calculations of hyperpolarizability tensors (β abc ) clearly show the dependence of SFG intensities on the polarity of crystallite packing within the SFG coherence length, which provides the basis for interpretation of the empirically observed SFG features of native cellulose in biological systems.

Electron-induced scattering dynamics of Boron, Aluminium and Gallium trihalides in the intermediate energy domain

NASA Astrophysics Data System (ADS)

Verma, Pankaj; Alam, Mohammad Jane; Ahmad, Shabbir; Antony, Bobby

2018-05-01

This article is focused on the calculation of electron-induced ionisation and total scattering cross sections by Boron, Aluminium and Gallium trihalide molecules in the intermediate energy domain. The computational formalism, spherical complex optical potential has been employed for the study of these two scattering cross sections. The ionisation cross section has been derived from the inelastic cross section using a semi-empirical method called complex scattering potential-ionisation contribution (CSP-ic) method. We have also calculated the ionisation cross section using the BEB theory with Hartree-Fock and density functional theory (DFT- ωB97XD) orbitals so that a comparison can be made with the cross sections predicted by CSP-ic method. For this theoretical study, we have also calculated polarisability and bond length of some targets which were not found in literature using DFT/B3LYP in Gaussian 09 software.

Experimental and theoretical study of topology and electronic correlations in PuB4

NASA Astrophysics Data System (ADS)

Choi, Hongchul; Zhu, Wei; Cary, S. K.; Winter, L. E.; Huang, Zhoushen; McDonald, R. D.; Mocko, V.; Scott, B. L.; Tobash, P. H.; Thompson, J. D.; Kozimor, S. A.; Bauer, E. D.; Zhu, Jian-Xin; Ronning, F.

2018-05-01

We synthesize single crystals of PuB4 using an Al-flux technique. Single-crystal diffraction data provide structural parameters for first-principles density functional theory (DFT) calculations. By computing the density of states, the Z2 topological invariant using the Wilson loop method, and the surface electronic structure from slab calculations, we find that PuB4 is a nonmagnetic strong topological insulator with a band gap of 254 meV. Our magnetic susceptibility, heat capacity, and resistivity measurements are consistent with this analysis, albeit with a smaller gap of 35 meV. DFT plus dynamical mean-field theory calculations show that electronic correlations reduce the size of the band gap, and provide better agreement with the value determined by resistivity. These results demonstrate that PuB4 is a promising actinide material to investigate the interplay of electronic correlations and nontrivial topology.

Towards a self-consistent dynamical nuclear model

NASA Astrophysics Data System (ADS)

Roca-Maza, X.; Niu, Y. F.; Colò, G.; Bortignon, P. F.

2017-04-01

Density functional theory (DFT) is a powerful and accurate tool, exploited in nuclear physics to investigate the ground-state and some of the collective properties of nuclei along the whole nuclear chart. Models based on DFT are not, however, suitable for the description of single-particle dynamics in nuclei. Following the field theoretical approach by A Bohr and B R Mottelson to describe nuclear interactions between single-particle and vibrational degrees of freedom, we have taken important steps towards the building of a microscopic dynamic nuclear model. In connection with this, one important issue that needs to be better understood is the renormalization of the effective interaction in the particle-vibration approach. One possible way to renormalize the interaction is by the so-called subtraction method. In this contribution, we will implement the subtraction method in our model for the first time and study its consequences.

Pressure-induced Lifshitz and structural transitions in NbAs and TaAs: experiments and theory

NASA Astrophysics Data System (ADS)

Nath Gupta, Satyendra; Singh, Anjali; Pal, Koushik; Muthu, D. V. S.; Shekhar, C.; Elghazali, Moaz A.; Naumov, Pavel G.; Medvedev, Sergey A.; Felser, C.; Waghmare, U. V.; Sood, A. K.

2018-05-01

High pressure Raman, resistivity and synchrotron x-ray diffraction studies on Weyl semimetals NbAs and TaAs have been carried out along with density functional theoretical (DFT) analysis to explain pressure induced structural and electronic topological phase transitions. The frequencies of first order Raman modes harden with increasing pressure, exhibiting a slope change at GPa for NbAs and GPa for TaAs. The resistivities of NbAs and TaAs exhibit a minimum at pressures close to these transition pressures and also a change in the bulk modulus is observed. Our first-principles calculations reveal that the transition is associated with an electronic Lifshitz transition at for NbAs while it is a structural phase transition from body centered tetragonal to hexagonal phase at for TaAs. Further, our DFT calculations show a structural phase transition at 24 GPa from body centered tetragonal phase to hexagonal phase.

First-principles atomistic Wulff constructions for an equilibrium rutile TiO2 shape modeling

NASA Astrophysics Data System (ADS)

Jiang, Fengzhou; Yang, Lei; Zhou, Dali; He, Gang; Zhou, Jiabei; Wang, Fanhou; Chen, Zhi-Gang

2018-04-01

Identifying the exposed surfaces of rutile TiO2 crystal is crucial for its industry application and surface engineering. In this study, the shape of the rutile TiO2 was constructed by applying equilibrium thermodynamics of TiO2 crystals via first-principles density functional theory (DFT) and Wulff principles. From the DFT calculations, the surface energies of six low-index stoichiometric facets of TiO2 are determined after the calibrations of crystal structure. And then, combined surface energy calculations and Wulff principles, a geometric model of equilibrium rutile TiO2 is built up, which is coherent with the typical morphology of fully-developed equilibrium TiO2 crystal. This study provides fundamental theoretical guidance for the surface analysis and surface modification of the rutile TiO2-based materials from experimental research to industry manufacturing.

Antiplasmodial Drugs in the Gas Phase: A CID and DFT Study of Quinolon-4( 1H)-Imine Derivatives

NASA Astrophysics Data System (ADS)

Amorim Madeira, Paulo J.; Sitoe, Ana Raquel Fernandes; Gonçalves, Daniel; Rodrigues, Tiago; Guedes, Rita C.; Lopes, Francisca; Moreira, Rui; Bronze, M. Rosário

2014-09-01

The gas-phase behavior of 12 quinolon-4( 1H)-imine derivatives with antiplasmodial activity was investigated using electrospray ionization tandem mass spectrometry together with collision induced dissociation and density functional theory (DFT) calculations. The most probable protonation site was predicted by calculating the proton affinity (PA) values for each possible protonation site and it was found to be the imine nitrogen for all compounds under study. Fragmentation pathways of the protonated molecules were proposed and the assignment of product ion structures was performed taking into account theoretical calculations. The nature of the quinoline substituent was found to influence the gas-phase behavior of the compounds under study. The data acquired allowed to bracket the proton affinity of the quinolin-4-imine scaffold, which can be a useful starting point to choose appropriate references for determining PA values of this scaffold.

Metastable structure of Li13Si4

NASA Astrophysics Data System (ADS)

Gruber, Thomas; Bahmann, Silvia; Kortus, Jens

2016-04-01

The Li13Si4 phase is one out of several crystalline lithium silicide phases, which is a potential electrode material for lithium ion batteries and contains a high theoretical specific capacity. By means of ab initio methods like density functional theory (DFT) many properties such as heat capacity or heat of formation can be calculated. These properties are based on the calculation of phonon frequencies, which contain information about the thermodynamical stability. The current unit cell of "Li13Si4" given in the ICSD database is unstable with respect to DFT calculations. We propose a modified unit cell that is stable in the calculations. The evolutionary algorithm EVO found a structure very similar to the ICSD one with both of them containing metastable lithium positions. Molecular dynamic simulations show a phase transition between both structures where these metastable lithium atoms move. This phase transition is achieved by a very fast one-dimensional lithium diffusion and stabilizes this phase.

Theoretical studies on a carbonaceous molecular bearing: association thermodynamics and dual-mode rolling dynamics† †Electronic supplementary information (ESI) available: Supplementary figures, tables and atomic coordinates of representative geometries. See DOI: 10.1039/c5sc00335k

PubMed Central

Nakamura, Kosuke; Hitosugi, Shunpei; Sato, Sota; Tokoyama, Hiroaki; Yamakado, Hideo; Ohno, Koichi

2015-01-01

The thermodynamics and dynamics of a carbonaceous molecular bearing comprising a belt-persistent tubular molecule and a fullerene molecule have been investigated using density functional theory (DFT). Among ten representative methods, two DFT methods afforded an association energy that reasonably reproduced the experimental enthalpy of –12.5 kcal mol–1 at the unique curved π-interface. The dynamics of the molecular bearing, which was assembled solely with van der Waals interactions, exhibited small energy barriers with maximum values of 2–3 kcal mol–1 for the rolling motions. The dynamic motions responded sensitively to the steric environment and resulted in two distinct motions, precession and spin, which explained the unique NMR observations that were not clarified in previous experimental studies. PMID:29142679

Mechanisms of Pyroelectricity in Three- and Two-Dimensional Materials

NASA Astrophysics Data System (ADS)

Liu, Jian; Pantelides, Sokrates T.

2018-05-01

Pyroelectricity is a very promising phenomenon in three- and two-dimensional materials, but first-principles calculations have not so far been used to elucidate the underlying mechanisms. Here we report density-functional theory (DFT) calculations based on the Born-Szigeti theory of pyroelectricity, by combining fundamental thermodynamics and the modern theory of polarization. We find satisfactory agreement with experimental data in the case of bulk benchmark materials, showing that the so-called electron-phonon renormalization, whose contribution has been traditionally viewed as negligible, is important. We predict out-of-plane pyroelectricity in the recently synthesized Janus MoSSe monolayer and in-plane pyroelectricity in the group-IV monochalcogenide GeS monolayer. It is notable that the so-called secondary pyroelectricity is found to be dominant in GeS monolayer. The present work opens a theoretical route to study the pyroelectric effect using DFT and provides a valuable tool in the search for new candidates for pyroelectric applications.

Self-consistent implementation of meta-GGA functionals for the ONETEP linear-scaling electronic structure package.

PubMed

Womack, James C; Mardirossian, Narbe; Head-Gordon, Martin; Skylaris, Chris-Kriton

2016-11-28

Accurate and computationally efficient exchange-correlation functionals are critical to the successful application of linear-scaling density functional theory (DFT). Local and semi-local functionals of the density are naturally compatible with linear-scaling approaches, having a general form which assumes the locality of electronic interactions and which can be efficiently evaluated by numerical quadrature. Presently, the most sophisticated and flexible semi-local functionals are members of the meta-generalized-gradient approximation (meta-GGA) family, and depend upon the kinetic energy density, τ, in addition to the charge density and its gradient. In order to extend the theoretical and computational advantages of τ-dependent meta-GGA functionals to large-scale DFT calculations on thousands of atoms, we have implemented support for τ-dependent meta-GGA functionals in the ONETEP program. In this paper we lay out the theoretical innovations necessary to implement τ-dependent meta-GGA functionals within ONETEP's linear-scaling formalism. We present expressions for the gradient of the τ-dependent exchange-correlation energy, necessary for direct energy minimization. We also derive the forms of the τ-dependent exchange-correlation potential and kinetic energy density in terms of the strictly localized, self-consistently optimized orbitals used by ONETEP. To validate the numerical accuracy of our self-consistent meta-GGA implementation, we performed calculations using the B97M-V and PKZB meta-GGAs on a variety of small molecules. Using only a minimal basis set of self-consistently optimized local orbitals, we obtain energies in excellent agreement with large basis set calculations performed using other codes. Finally, to establish the linear-scaling computational cost and applicability of our approach to large-scale calculations, we present the outcome of self-consistent meta-GGA calculations on amyloid fibrils of increasing size, up to tens of thousands of atoms.

Self-consistent implementation of meta-GGA functionals for the ONETEP linear-scaling electronic structure package

NASA Astrophysics Data System (ADS)

Womack, James C.; Mardirossian, Narbe; Head-Gordon, Martin; Skylaris, Chris-Kriton

2016-11-01

Accurate and computationally efficient exchange-correlation functionals are critical to the successful application of linear-scaling density functional theory (DFT). Local and semi-local functionals of the density are naturally compatible with linear-scaling approaches, having a general form which assumes the locality of electronic interactions and which can be efficiently evaluated by numerical quadrature. Presently, the most sophisticated and flexible semi-local functionals are members of the meta-generalized-gradient approximation (meta-GGA) family, and depend upon the kinetic energy density, τ, in addition to the charge density and its gradient. In order to extend the theoretical and computational advantages of τ-dependent meta-GGA functionals to large-scale DFT calculations on thousands of atoms, we have implemented support for τ-dependent meta-GGA functionals in the ONETEP program. In this paper we lay out the theoretical innovations necessary to implement τ-dependent meta-GGA functionals within ONETEP's linear-scaling formalism. We present expressions for the gradient of the τ-dependent exchange-correlation energy, necessary for direct energy minimization. We also derive the forms of the τ-dependent exchange-correlation potential and kinetic energy density in terms of the strictly localized, self-consistently optimized orbitals used by ONETEP. To validate the numerical accuracy of our self-consistent meta-GGA implementation, we performed calculations using the B97M-V and PKZB meta-GGAs on a variety of small molecules. Using only a minimal basis set of self-consistently optimized local orbitals, we obtain energies in excellent agreement with large basis set calculations performed using other codes. Finally, to establish the linear-scaling computational cost and applicability of our approach to large-scale calculations, we present the outcome of self-consistent meta-GGA calculations on amyloid fibrils of increasing size, up to tens of thousands of atoms.

Effects of doping of calcium atom(s) on structural, electronic and optical properties of binary strontium chalcogenides - A theoretical investigation using DFT based FP-LAPW methodology

NASA Astrophysics Data System (ADS)

Bhattacharjee, Rahul; Chattopadhyaya, Surya

2017-09-01

The effects of doping of Ca atom(s) on structural, electronic and optical properties of binary strontium chalcogenide semiconductor compounds have been investigated theoretically using DFT based FP-LAPW approach by modeling the rock-salt (B1) ternary alloys CaxSr1-xS, CaxSr1-xSe and CaxSr1-xTe at some specific concentrations 0 ≤ x ≤ 1 and studying their aforesaid properties. The exchange-correlation potentials for their structural properties have been computed using the Wu-Cohen generalized-gradient approximation (WC-GGA) scheme, while those for the electronic and optical properties have been computed using recently developed Tran-Blaha modified Becke-Johnson (TB-mBJ) scheme. In addition, we have computed the electronic and optical properties with the traditional BLYP and PBE-GGA schemes for comparison. The atomic and orbital origin of different electronic states in the band structure of each of the compounds have been identified from the respective density of states (DOS). Using the approach of Zunger and co-workers, the microscopic origin of band gap bowing has been discussed in term of volume deformation, charge exchange and structural relaxation. Bonding characteristics among the constituent atoms of each of the specimens have been discussed from their charge density contour plots. Optical properties of the binary compounds and ternary alloys have been investigated theoretically in terms of their respective dielectric function, refractive index, normal incidence reflectivity and optical conductivity. Several calculated results have been compared with available experimental and other theoretical data.

New five coordinated supramolecular structured cadmium complex as precursor for CdO nanoparticles: Synthesis, crystal structure, theoretical and 3D Hirshfeld surface analyses

NASA Astrophysics Data System (ADS)

Ghanbari Niyaky, S.; Montazerozohori, M.; Masoudiasl, A.; White, J. M.

2017-03-01

In this paper, a combined experimental and theoretical study on a new CdLBr2 complex (L = N1-(2-bromobenzylidene)-N2-(2-((E)-(2-bromobenzylidene) amino)ethyl) ethane-1,2-diamine) synthesized via template method, is described. The crystal structure analysis of the complex indicates that, the Cd(II) ion is centered in a distorted square pyramidal space constructed by three iminic nitrogens of the ligand as well as two bromide anions. More analysis of crystal packing proposed a supramolecular structure stabilized by some non-covalent interactions such as Br⋯Br and Xsbnd H⋯Br (X = N and C) in solid state. Furthermore, 3D Hirshfeld surface analyses and DFT studies were applied for theoretical investigation of the complexes. Theoretical achievements were found in a good agreement with respect to the experimental data. To evaluate the nature of bonding and the strength of the intra and inter-molecular interactions a natural bond orbital (NBO) analysis on the complex structure was performed. Time dependent density functional theory (TD-DFT) was also applied to predict the electronic spectral data of the complex as compared with the experimental ones. CdLBr2 complex as nano-structure compound was also prepared under ultrasonic conditions and characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). Finally, it was found that the cadmium complex can be used as a suitable precursor for preparation of CdO nanoparticles via calcination process at 600 °C under air atmosphere.

X-ray structure determination, Hirshfeld surface analysis, spectroscopic (FT-IR, NMR, UV-Vis, fluorescence), non-linear optical properties, Fukui function and chemical activity of 4‧-(2,4-dimethoxyphenyl)-2,2‧:6‧,2″-terpyridine

NASA Astrophysics Data System (ADS)

Demircioğlu, Zeynep; Yeşil, Ahmet Emin; Altun, Mehmet; Bal-Demirci, Tülay; Özdemir, Namık

2018-06-01

The compound 4‧-(2,4-dimethoxyphenyl)-2,2‧:6‧,2″-terpyridine (Mtpyr) was synthesized and investigated using X-ray single crystal structure determination, combined with Hirshfeld topology analysis of the molecular packing. In addition, Mtpyr was characterized by experimental and theoretical FT-IR, UV-Vis, 1H NMR, 13C NMR and fluorescence emission spectra. The optimized molecular geometry (bond length, bond angle, torsion angle), the complete vibrational frequency and all other theoretical computations were calculated by using density functional theory (DFT) B3LYP method with the help of 6-311++G(d,p) basis set. From the recorded UV-Vis spectrum, the electronic properties such as excitation energies, wavelength and oscillator strength are evaluated by TD-DFT in chloroform solution. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by the gauge-independent atomic orbital (GIAO) method and compared with experimental results. The calculated HOMO-LUMO band gap energies confirmed that charge transfer and chemical stability within the molecule. The hyperconjugative interaction energy E(2) and electron densities of donor (i) and acceptor (j) bonds were calculated using natural bond orbital (NBO) analysis. Besides Mulliken and natural population charges (NPA), non-linear optic properties (NLO), Fukui Function analysis, molecular electrostatic potential (MEP) were also computed which helps to identifying the electrophilic/nucleophilic nature.

Infrared matrix-isolation and theoretical studies of the reactions of ferrocene with ozone.

PubMed

Kugel, Roger W; Pinelo, Laura F; Ault, Bruce S

2015-03-19

The reactions between ferrocene (Cp2Fe) (2a) and ozone (O3) were studied using low-temperature matrix-isolation techniques coupled with theoretical density functional theory (DFT) calculations. Co-deposition of Ar/Cp2Fe and Ar/O3 gas mixtures onto a cryogenically cooled CsI window produced a dark-green charge-transfer complex, Cp2Fe-O3, that photodecomposed upon red (λ ≥ 600 nm) and infrared (λ ≥ 1000 nm) irradiation but was stable to green or blue irradiation. Products of photodecomposition were characterized by FT-IR, oxygen-18 labeling, and DFT calculations using the B3LYP functionals and the 6-311G++(d,2p) basis set. Likely, photochemical products included four structures having the molecular formula C10H10FeO, identified by DFT calculations based on their calculated infrared spectra and (18)O isotope shifts. Each of these calculated molecules had one intact and fully coordinated η(5)-C5H5 cyclopentadienyl (Cp) ring and (1) an η(5)-C5H5O cyclic ether (pyran ring) (2b), (2) an η(4)-C5H5O linear aldehyde (2c), (3) a bidentate cyclic aldehyde with a seven-membered ring including the iron atom (2d), or (4) an Fe-O bond and an η(2)-C5H5 (Cp) ring (2e). No conclusive evidence for a gas-phase thermal reaction between ferrocene and ozone was observed under the conditions of these experiments. However, strong evidence for a surface-catalyzed thermal reaction was observed in merged-jet experiments wherein the gases were premixed before deposition. Surface-catalyzed ferrocene-ozone reaction products included a thin film of Fe2O3 observed on the walls of the merged tube as well as cyclopentadiene (C5H6), cyclopentadienone (C5H4O), and further oxidation products observed in the matrix. Possible mechanisms for both the photochemical and the thermal reactions are discussed.

Photoelectron Angular Distributions of Transition Metal Dioxide Anions - a joint experimental and theoretical study

NASA Astrophysics Data System (ADS)

Iordanov, Ivan; Gunaratne, Dasitha; Harmon, Christopher; Sofo, Jorge; Castleman, A. W., Jr.

2012-02-01

Angular-resolved photoelectron spectroscopy (PES) studies of the MO2- (M=Ti, Zr, Hf, Co, Rh) clusters are presented for the first time along with theoretical calculations of their properties. We confirm previously reported non-angular PES results for the vertical detachment energies (VDE), vibrational energies and geometric structures of these clusters and further explore the effect of the 'lanthanide contraction' on the MO2- clusters by comparing the electronic spectra of 4d and 5d transition metal dioxides. Angular-resolved PES provides the angular momentum contributions to the HOMO of these clusters and we use theoretical calculations to examine the HOMO and compare to our experimental results. First-principles calculations are done using both density functional theory (DFT) and the coupled-cluster, singles, doubles and triples (CCSD(T)) methods.

Experimental (FTIR, Raman, UV-visible and PL) and theoretical (DFT and TDDFT) studies on bis(8-hydroxyquinolinium) tetrachlorocobaltate(II) compound

NASA Astrophysics Data System (ADS)

Chaouachi, Soumaya; Elleuch, Slim; Hamdi, Besma; Zouari, Ridha

2016-12-01

The purpose of this paper is to present the chemical preparation, crystal structure, vibrational study and optical features for new organic-inorganic compound [C9H8NO]2CoCl4 abbreviated [8-HQ]2CoCl4. The structural study by X-ray diffraction prove that this compound crystallize in a monoclinic unit-cell with space group C2/c (point group 2/m = C2h). It is built of tetrahedra [CoCl4]2- anions and (C9H8NO)+ cations in the 1/2 ratio. The crystal structure is stabilized by network three-dimensional of Nsbnd H⋯Cl, Nsbnd H⋯O, Osbnd H⋯Cl, Csbnd H⋯Cl hydrogen bonds, and offset π-π stacking interactions. Also, the Hirshfeld Surface projections and Fingerprint plots were elucidated the relative contribution of the type, nature and explore the H⋯Cl, C⋯H, C⋯C, C⋯N, H⋯O intermolecular contacts in the crystal in a visual manner. Furthermore, vibrational analysis of the structural groups in the compound was carried out by both Fourier transforms infrared (FT-IR) and Raman spectra. The spectral data are complemented by good information at the region characteristic of metal-ligand, which evidences coordination through the compound. The optical properties of the crystal were studied by using optical absorption UV-visible and photoluminescence (PL) spectroscopy studies. Theoretical calculations were performed using density functional theory (DFT) at (DFT/B3LYP/LanL2DZ) level in the aim of aiding in studying structural, vibrational and optical properties of the investigated compound. Good relationship consistency is found between the experimental and theoretical studies. Inspection of the optical properties has lead to confirm the exhibition of a green photoluminescence and the occurrence of charge transfer phenomenon in this material.

Vibrational and structural study of onopordopicrin based on the FTIR spectrum and DFT calculations.

PubMed

Chain, Fernando E; Romano, Elida; Leyton, Patricio; Paipa, Carolina; Catalán, César A N; Fortuna, Mario; Brandán, Silvia Antonia

2015-01-01

In the present work, the structural and vibrational properties of the sesquiterpene lactone onopordopicrin (OP) were studied by using infrared spectroscopy and density functional theory (DFT) calculations together with the 6-31G(∗) basis set. The harmonic vibrational wavenumbers for the optimized geometry were calculated at the same level of theory. The complete assignment of the observed bands in the infrared spectrum was performed by combining the DFT calculations with Pulay's scaled quantum mechanical force field (SQMFF) methodology. The comparison between the theoretical and experimental infrared spectrum demonstrated good agreement. Then, the results were used to predict the Raman spectrum. Additionally, the structural properties of OP, such as atomic charges, bond orders, molecular electrostatic potentials, characteristics of electronic delocalization and topological properties of the electronic charge density were evaluated by natural bond orbital (NBO), atoms in molecules (AIM) and frontier orbitals studies. The calculated energy band gap and the chemical potential (μ), electronegativity (χ), global hardness (η), global softness (S) and global electrophilicity index (ω) descriptors predicted for OP low reactivity, higher stability and lower electrophilicity index as compared with the sesquiterpene lactone cnicin containing similar rings. Copyright © 2015 Elsevier B.V. All rights reserved.

Electronic structure and nature of the ground state of the mixed-valence binuclear tetra(mu-1,8-naphthyridine-N,N')-bis(halogenonickel) tetraphenylborate complexes: experimental and DFT characterization.

PubMed

Bencini, Alessandro; Berti, Elisabetta; Caneschi, Andrea; Gatteschi, Dante; Giannasi, Elisa; Invernizzi, Ivana

2002-08-16

The ground state electronic structure of the mixed-valence systems [Ni(2)(napy)(4)X(2)](BPh(4)) (napy=1,8-naphthyridine; X=Cl, Br, I) was studied with combined experimental (X-ray diffraction, temperature dependence of the magnetic susceptibility, and high-field EPR spectroscopy) and theoretical (DFT) methods. The zero-field splitting (zfs) ground S=3/2 spin state is axial with /D/ approximately 3 cm(-1). The iodide derivative was found to be isostructural with the previously reported bromide complex, but not isomorphous. The compound crystallizes in the monoclinic system, space group P2(1)/n, with a=17.240(5), b=26.200(5), c=11.340(5) A, beta=101.320(5) degrees. DFT calculations were performed on the S=3/2 state to characterize the ground state potential energy surface as a function of the nuclear displacements. The molecules can thus be classified as Class III mixed-valence compounds with a computed delocalization parameter, B=3716, 3583, and 3261 cm(-1) for the Cl, Br, and I derivatives, respectively.

Time-Dependent Density Functional Theory for Extreme Environments

NASA Astrophysics Data System (ADS)

Baczewski, Andrew; Magyar, Rudolph; Shulenburger, Luke

2013-10-01

In recent years, DFT-MD has been shown to be a powerful tool for calculating the equation of state and constitutive properties of warm dense matter (WDM). These studies are validated through a number of experiments, including recently developed X-Ray Thomson Scattering (XRTS) techniques. Here, electronic temperatures and densities of WDM are accessible through x-ray scattering data, which is related to the system's dynamic structure factor (DSF)-a quantity that is accessible through DFT-MD calculations. Previous studies predict the DSF within the Born-Oppenheimer approximation, with the electronic state computed using Mermin DFT. A capability for including more general coupled electron-ion dynamics is desirable, to study both the effect on XRTS observables and the broader problem of electron-ion energy transfer in extreme WDM conditions. Progress towards such a capability will be presented, in the form of an Ehrenfest MD framework using TDDFT. Computational challenges and open theoretical questions will be discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Security Administration under contract DE-AC04-94AL85000.

Density functional theory based molecular dynamics study of hydration and electronic properties of aqueous La(3+).

PubMed

Terrier, Cyril; Vitorge, Pierre; Gaigeot, Marie-Pierre; Spezia, Riccardo; Vuilleumier, Rodolphe

2010-07-28

Structural and electronic properties of La(3+) immersed in bulk water have been assessed by means of density functional theory (DFT)-based Car-Parrinello molecular dynamics (CPMD) simulations. Correct structural properties, i.e., La(III)-water distances and La(III) coordination number, can be obtained within the framework of Car-Parrinello simulations providing that both the La pseudopotential and conditions of the dynamics (fictitious mass and time step) are carefully set up. DFT-MD explicitly treats electronic densities and is shown here to provide a theoretical justification to the necessity of including polarization when studying highly charged cations such as lanthanoids(III) with classical MD. La(3+) was found to strongly polarize the water molecules located in the first shell, giving rise to dipole moments about 0.5 D larger than those of bulk water molecules. Finally, analyzing Kohn-Sham orbitals, we found La(3+) empty 4f orbitals extremely compact and to a great extent uncoupled from the water conduction band, while the 5d empty orbitals exhibit mixing with unoccupied states of water.

Synthesis, molecular structure and spectroscopic investigations of novel fluorinated spiro heterocycles.

PubMed

Islam, Mohammad Shahidul; Al-Majid, Abdullah Mohammed; Barakat, Assem; Soliman, Saied M; Ghabbour, Hazem A; Quah, Ching Kheng; Fun, Hoong-Kun

2015-05-07

This paper describes an efficient and regioselective method for the synthesis of novel fluorinated spiro-heterocycles in excellent yield by cascade [5+1] double Michael addition reactions. The compounds 7,11-bis(4-fluorophenyl)-2,4-dimethyl- 2,4-diazaspiro[5.5] undecane-1,3,5,9-tetraone (3a) and 2,4-dimethyl-7,11-bis (4-(trifluoromethyl)phenyl)-2,4-diazaspiro[5.5]undecane-1,3,5,9-tetraone (3b) were characterized by single-crystal X-ray diffraction, FT-IR and NMR techniques. The optimized geometrical parameters, infrared vibrational frequencies and NMR chemical shifts of the studied compounds have also been calculated using the density functional theory (DFT) method, using Becke-3-Lee-Yang-Parr functional and the 6-311G(d,p) basis set. There is good agreement between the experimentally determined structural parameters, vibrational frequencies and NMR chemical shifts of the studied compounds and those predicted theoretically. The calculated natural atomic charges using NBO method showed higher polarity of 3a compared to 3b.The calculated electronic spectra are also discussed based on the TD-DFT calculations.

Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method.

PubMed

Pasha, M A; Siddekha, Aisha; Mishra, Soni; Azzam, Sadeq Hamood Saleh; Umapathy, S

2015-02-05

In the present study, 2'-nitrophenyloctahydroquinolinedione and its 3'-nitrophenyl isomer were synthesized and characterized by FT-IR, FT-Raman, (1)H NMR and (13)C NMR spectroscopy. The molecular geometry, vibrational frequencies, (1)H and (13)C NMR chemical shift values of the synthesized compounds in the ground state have been calculated by using the density functional theory (DFT) method with the 6-311++G (d,p) basis set and compared with the experimental data. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution using GAR2PED programme. Isotropic chemical shifts for (1)H and (13)C NMR were calculated using gauge-invariant atomic orbital (GIAO) method. The experimental vibrational frequencies, (1)H and (13)C NMR chemical shift values were found to be in good agreement with the theoretical values. On the basis of vibrational analysis, molecular electrostatic potential and the standard thermodynamic functions have been investigated. Copyright © 2014 Elsevier B.V. All rights reserved.

A density-functional study on the electronic and vibrational properties of layered antimony telluride.

PubMed

Stoffel, Ralf P; Deringer, Volker L; Simon, Ronnie E; Hermann, Raphaël P; Dronskowski, Richard

2015-03-04

We present a comprehensive survey of electronic and lattice-dynamical properties of crystalline antimony telluride (Sb2Te3). In a first step, the electronic structure and chemical bonding have been investigated, followed by calculations of the atomic force constants, phonon dispersion relationships and densities of states. Then, (macroscopic) physical properties of Sb2Te3 have been computed, namely, the atomic thermal displacement parameters, the Grüneisen parameter γ, the volume expansion of the lattice, and finally the bulk modulus B. We compare theoretical results from three popular and economic density-functional theory (DFT) approaches: the local density approximation (LDA), the generalized gradient approximation (GGA), and a posteriori dispersion corrections to the latter. Despite its simplicity, the LDA shows excellent performance for all properties investigated-including the Grüneisen parameter, which only the LDA is able to recover with confidence. In the absence of computationally more demanding hybrid DFT methods, the LDA seems to be a good choice for further lattice dynamical studies of Sb2Te3 and related layered telluride materials.

Synthesis and spectral properties of Methyl-Phenyl pyrazoloquinoxaline fluorescence emitters: Experiment and DFT/TDDFT calculations

NASA Astrophysics Data System (ADS)

Gąsiorski, P.; Matusiewicz, M.; Gondek, E.; Uchacz, T.; Wojtasik, K.; Danel, A.; Shchur, Ya.; Kityk, A. V.

2018-01-01

Paper reports the synthesis and spectroscopic studies of two novel 1-Methyl-3-phenyl-1H-pyrazolo[3,4-b]quinoxaline (PQX) derivatives with 6-substituted methyl (MeMPPQX) or methoxy (MeOMPPQX) side groups. The optical absorption and fluorescence emission spectra are recorded in solvents of different polarity. Steady state and time-resolved spectroscopy provide photophysical characterization of MeMPPQX and MeOMPPQX dyes as materials for potential luminescence or electroluminescence applications. Measured optical absorption and fluorescence emission spectra are compared with quantum-chemical DFT/TDDFT calculations using long-range corrected xc-functionals, LRC-BLYP and CAM-B3LYP in combination with self-consistent reaction field model based on linear response (LR), state specific (SS) or corrected linear response (CLR) solvations. Performances of relevant theoretical models and approaches are compared. The reparameterized LRC-BLYP functional (ω = 0.231 Bohr-1) in combination with CLR solvation provides most accurate prediction of both excitation and emission energies. The MeMPPQX and MeOMPPQX dyes represent efficient fluorescence emitters in blue-green region of the visible spectra.

DFT/TDDFT investigation on the photophysical properties of a series of phosphorescent cyclometalated complexes based on the benchmark complex FIrpic

NASA Astrophysics Data System (ADS)

Han, Deming; Gong, Ping; Lv, Shuhui; Zhao, Lihui; Zhao, Henan

2018-05-01

The photophysical properties of four Ir(III) complexes have been investigated by means of the density functional theory/time-dependent density functional theory (DFT/TDDFT). The effect of the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption and phosphorescent properties has been studied. The theoretical calculation shows that the lowest-lying singlet absorptions for complexes 1-4 are located at 387, 385, 418 and 386 nm, respectively. For 1-4, the phosphorescence at 465, 485, 494 and 478 nm is mainly attributed to the LUMO → HOMO and LUMO → HOMO-1 transition configurations characteristics. In addition, ionisation potential (IP), electron affinities (EAs) and reorganisation energy have been investigated to evaluate the charge transfer and balance properties between hole and electron. The balance of the reorganisation energies for complex 3 is better than others. The difference between hole transport and electron transport for complex 3 is the smallest among these complexes, which is beneficial to achieve the hole and electron transfer balance in emitting layer.

First principles DFT study of dye-sensitized CdS quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Kalpna; Singh, Kh. S.; Kishor, Shyam, E-mail: shyam387@gmail.com

2014-04-24

Dye-sensitized quantum dots (QDs) are considered promising candidates for dye-sensitized solar cells. In order to maximize their efficiency, detailed theoretical studies are important. Here, we report a first principles density functional theory (DFT) investigation of experimentally realized dye - sensitized QD / ligand systems, viz., Cd{sub 16}S{sub 16}, capped with acetate molecules and a coumarin dye. The hybrid B3LYP functional and a 6−311+G(d,p)/LANL2dz basis set are used to study the geometric, energetic and electronic properties of these clusters. There is significant structural rearrangement in all the clusters studied - on the surface for the bare QD, and in the positionsmore » of the acetate / dye ligands for the ligated QDs. The density of states (DOS) of the bare QD shows states in the band gap, which disappear on surface passivation with the acetate molecules. Interestingly, in the dye-sensitised QD, the HOMO is found to be localized mainly on the dye molecule, while the LUMO is on the QD, as required for photo-induced electron injection from the dye to the QD.« less

Mono azo dyes derived from 5-nitroanthranilic acid: Synthesis, absorption properties and DFT calculations

NASA Astrophysics Data System (ADS)

Karabacak Atay, Çiğdem; Gökalp, Merve; Kart, Sevgi Özdemir; Tilki, Tahir

2017-08-01

Four new azo dyes: 2-[(3,5-diamino-1H-pyrazol-4-yl)diazenyl]-5-nitrobenzoic acid (A), 2-[(3-hydroxy-5-methyl-1H-pyrazol-4-yl)diazenyl]-5-nitrobenzoic acid (B), 2-[(3,5-dimethyl-1H-pyrazol-4-yl)diazenyl]-5-nitrobenzoic acid (C) and 2-[(5-amino-3-methyl-1H-pyrazol-4-yl)diazenyl]-5-nitrobenzoic acid (D) which have the same 4-nitrobenzene/azo/pyrazole skeleton and different substituted groups are synthesized in this work. The structures and spectroscopic properties of these new azo dyes are characterized by using spectroscopic methods such as FT-IR, 1H NMR, 13C NMR and UV-vis. Their solvatochromic properties in chloroform, acetic acid, methanol, dimethylformamide (DMF) and dimethylsulphoxide (DMSO) are studied. Moreover, molecular structures and some spectroscopic properties of azo dyes are investigated by utilizing the quantum computational chemistry method based on Density Functional Theory (DFT) employing B3LYP hybrid functional level with 6-31G(d) basis set. It is seen that experimental and theoretical results are compatible with each other.

Investigation of different physical aspects such as structural, mechanical, optical properties and Debye temperature of Fe2ScM (M=P and As) semiconductors: A DFT-based first principles study

NASA Astrophysics Data System (ADS)

Ali, Md. Lokman; Rahaman, Md. Zahidur

2018-04-01

By using first principles calculation dependent on the density functional theory (DFT), we have investigated the mechanical, structural properties and the Debye temperature of Fe2ScM (M=P and As) compounds under various pressures up to 60 GPa. The optical properties have been investigated under zero pressure. Our calculated optimized structural parameters of both the materials are in good agreement with other theoretical predictions. The calculated elastic constants show that Fe2ScM (M=P and As) compounds are mechanically stable under external pressure below 60 GPa. From the elastic constants, the shear modulus G, the bulk modulus B, Young’s modulus E, anisotropy factor A and Poisson’s ratio ν are calculated by using the Voigt-Reuss-Hill approximation. The Debye temperature and average sound velocities are also investigated from the obtained elastic constants. The detailed analysis of all optical functions reveals that both compounds are good dielectric material.

FT-IR, FT-Raman spectra and DFT calculations of melaminium perchlorate monohydrate

NASA Astrophysics Data System (ADS)

Kanagathara, N.; Marchewka, M. K.; Drozd, M.; Renganathan, N. G.; Gunasekaran, S.; Anbalagan, G.

2013-08-01

Melaminium perchlorate monohydrate (MPM), an organic material has been synthesized by slow solvent evaporation method at room temperature. Powder X-ray diffraction analysis confirms that MPM crystal belongs to triclinic system with space group P-1. FTIR and FT Raman spectra are recorded at room temperature. Functional group assignment has been made for the melaminium cations and perchlorate anions. Vibrational spectra have also been discussed on the basis of quantum chemical density functional theory (DFT) calculations using Firefly (PC GAMESS) version 7.1 G. Vibrational frequencies are calculated and scaled values are compared with experimental values. The assignment of the bands has been made on the basis of the calculated PED. The Mulliken charges, HOMO-LUMO orbital energies are analyzed directly from Firefly program log files and graphically illustrated. HOMO-LUMO energy gap and other related molecular properties are also calculated. The theoretically constructed FT-IR and FT-Raman spectra of MPM coincide with the experimental one. The chemical structure of the compound has been established by 1H and 13C NMR spectra. No detectable signal was observed during powder test for second harmonic generation.

Infrared multiple photon dissociation spectroscopy of sodium and potassium chlorate anions.

PubMed

Dain, Ryan P; Leavitt, Christopher M; Oomens, Jos; Steill, Jeffrey D; Groenewold, Gary S; Van Stipdonk, Michael J

2010-01-01

The structures of gas-phase, metal chlorate anions with the formula [M(ClO(3))(2)](-), M = Na and K, were determined using tandem mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. Structural assignments for both anions are based on comparisons of the experimental vibrational spectra for the two species with those predicted by density functional theory (DFT) and involve conformations that feature either bidentate or tridentate coordination of the cation by chlorate. Our results strongly suggest that a structure in which both chlorate anions are bidentate ligands is preferred for [Na(ClO(3))(2)](-). However, for [K(ClO(3))(2)](-) the best agreement between experimental and theoretical spectra is obtained from a composite of predicted spectra for which the chlorate anions are either both bidentate or both tridentate ligands. In general, we find that the overall accuracy of DFT calculations for prediction of IR spectra is dependent on both functional and basis set, with best agreement achieved using frequencies generated at the B3LYP/6-311+g(3df) level of theory. Copyright 2009 John Wiley & Sons, Ltd.

Synthesis, crystal structure analysis, spectral investigations, DFT computations and molecular dynamics and docking study of 4-benzyl-5-oxomorpholine-3-carbamide, a potential bioactive agent

NASA Astrophysics Data System (ADS)

Murthy, P. Krishna; Sheena Mary, Y.; Shyma Mary, Y.; Panicker, C. Yohannan; Suneetha, V.; Armaković, Stevan; Armaković, Sanja J.; Van Alsenoy, C.; Suchetan, P. A.

2017-04-01

4-benzyl-5-oxomorpholine-3-carbamide has been synthesized; single crystals were grown by slow evaporation solution growth technique at room temperature and characterized by single crystal X-ray diffraction, FT-IR, FT-Raman and 1H-NMR. The compound crystallizes in the monoclinic space group P21/n. The molecular geometry of the compound was optimized by using Density Functional Theory (DFT/B3LYP) method with 6-311++G(d,p) basis set in the ground state and geometric parameters are in agreement with the X-ray analysis results of the structure. The experimental vibrational spectra were compared with the calculated spectra and each vibrational wave number was assigned on the basis of potential energy distribution (PED). The electronic and charge transfer properties have been explained on the basis of highest occupied molecular orbital's (HOMOs) and lowest unoccupied molecular orbital's (LUMOs). Besides molecular electrostatic potential (MEP), frontier molecular orbital's (FMOs), some global reactivity descriptors, thermodynamic properties, non-linear optical (NLO) behavior and Mullikan charge analysis of the title compound were computed with the same method in gas phase, theoretically. Potential reactive sites of the title compound have been identified by average local ionization energy and Fukui functions, both mapped to the electron density surface. Bond dissociation energies for all single acyclic bonds have been calculated in order to investigate autoxidation and degradation properties of the title compound. Atoms with pronounced interactions with water molecules have been detected by calculations of radial distribution functions after molecular dynamics simulations. The experimental results are compared with the theoretical calculations using DFT methods for the fortification of the paper. Further the docking studies revealed that the title compound as a docked ligand forms a stable complex with pyrrole inhibitor with a binding affinity value of -7.5 kcal/mol. This suggests that the title compound might exhibit inhibitory activity against pyrrole inhibitor. To confirm the potential practical applicability of the title compound antimicrobial activity was tested against gram negative and gram positive bacteria.

Identifying the Thermal Decomposition Mechanism of Guaiacol on Pt(111): An Integrated X-ray Photoelectron Spectroscopy and Density Functional Theory Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hensley, Alyssa J.; Wockel, Claudia; Gleichweit, Christoph

Using a concerted effort from both experiment and theory, we determine the thermal decomposition mechanism for guaiacol on Pt(111), a reaction of interest in the area of bio-oil upgrading. This work serves as a demonstration of the power of combining in situ temperature-programmed X-ray photoelectron spectroscopy cos (TPXPS) and density functional theory (DFT) to elucidate complex reaction mechanisms occurring on heterogeneous surfaces. At low temperature (230 K), guaiacol was found to chemisorb with the aromatic ring parallel to the Pt(111) surface with five distinct carbon species and three oxygen species. As the temperature was increased, TPXPS showed several significant changesmore » to the surface species. The increase in the species associated with the decomposition of the functional groups of guaiacol is followed by their subsequent disappearance and an increase in the nonaromatic carbon signal. On the basis of an energetic analysis of the various mechanisms using DFT, along with the comparison of the experimentally and theoretically derived core-level binding energies, we determined that guaiacol's decomposition mechanism occurs via the dehydrogenation of both the methyl and hydroxyl functional groups, followed by demethylation of the CH2 or CH group to form 1,2-benzoquinone. Further heating to above 375 K likely breaks the aromatic ring and results in the rapid formation and desorption of CO, accounting for the disappearance of the 0 is signal above 450 K These results show that a knowledgeable application of TPXPS and DFT can result in the quantitative identification of surface species during complex reactions, providing insight useful for the design of future heterogeneous surfaces.« less

0–0 Energies Using Hybrid Schemes: Benchmarks of TD-DFT, CIS(D), ADC(2), CC2, and BSE/GW formalisms for 80 Real-Life Compounds

PubMed Central

2015-01-01

The 0–0 energies of 80 medium and large molecules have been computed with a large panel of theoretical formalisms. We have used an approach computationally tractable for large molecules, that is, the structural and vibrational parameters are obtained with TD-DFT, the solvent effects are accounted for with the PCM model, whereas the total and transition energies have been determined with TD-DFT and with five wave function approaches accounting for contributions from double excitations, namely, CIS(D), ADC(2), CC2, SCS-CC2, and SOS-CC2, as well as Green’s function based BSE/GW approach. Atomic basis sets including diffuse functions have been systematically applied, and several variations of the PCM have been evaluated. Using solvent corrections obtained with corrected linear-response approach, we found that three schemes, namely, ADC(2), CC2, and BSE/GW allow one to reach a mean absolute deviation smaller than 0.15 eV compared to the measurements, the two former yielding slightly better correlation with experiments than the latter. CIS(D), SCS-CC2, and SOS-CC2 provide significantly larger deviations, though the latter approach delivers highly consistent transition energies. In addition, we show that (i) ADC(2) and CC2 values are extremely close to each other but for systems absorbing at low energies; (ii) the linear-response PCM scheme tends to overestimate solvation effects; and that (iii) the average impact of nonequilibrium correction on 0–0 energies is negligible. PMID:26574326

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sim, Eunji; Kim, Min-Cheol; Burke, Kieron

We investigate dissociation of diatomic molecules using standard density functional theory (DFT) and density-corrected density functional theory (DC-DFT) compared with CCSD(T) results as reference. The results show the difference between the HOMO values of dissociated atomic species often can be used as an indicator whether DFT would predict the correct dissociation limit. DFT predicts incorrect dissociation limits and charge distribution in molecules or molecular ions when the fragments have large HOMO differences, while DC-DFT and CCSD(T) do not. The criteria for large HOMO difference is about 2 ∼ 4 eV.

Thermal density functional theory, ensemble density functional theory, and potential functional theory for warm dense matter

NASA Astrophysics Data System (ADS)

Pribram-Jones, Aurora

Warm dense matter (WDM) is a high energy phase between solids and plasmas, with characteristics of both. It is present in the centers of giant planets, within the earth's core, and on the path to ignition of inertial confinement fusion. The high temperatures and pressures of warm dense matter lead to complications in its simulation, as both classical and quantum effects must be included. One of the most successful simulation methods is density functional theory-molecular dynamics (DFT-MD). Despite great success in a diverse array of applications, DFT-MD remains computationally expensive and it neglects the explicit temperature dependence of electron-electron interactions known to exist within exact DFT. Finite-temperature density functional theory (FT DFT) is an extension of the wildly successful ground-state DFT formalism via thermal ensembles, broadening its quantum mechanical treatment of electrons to include systems at non-zero temperatures. Exact mathematical conditions have been used to predict the behavior of approximations in limiting conditions and to connect FT DFT to the ground-state theory. An introduction to FT DFT is given within the context of ensemble DFT and the larger field of DFT is discussed for context. Ensemble DFT is used to describe ensembles of ground-state and excited systems. Exact conditions in ensemble DFT and the performance of approximations depend on ensemble weights. Using an inversion method, exact Kohn-Sham ensemble potentials are found and compared to approximations. The symmetry eigenstate Hartree-exchange approximation is in good agreement with exact calculations because of its inclusion of an ensemble derivative discontinuity. Since ensemble weights in FT DFT are temperature-dependent Fermi weights, this insight may help develop approximations well-suited to both ground-state and FT DFT. A novel, highly efficient approach to free energy calculations, finite-temperature potential functional theory, is derived, which has the potential to transform the simulation of warm dense matter. As a semiclassical method, it connects the normally disparate regimes of cold condensed matter physics and hot plasma physics. This orbital-free approach captures the smooth classical density envelope and quantum density oscillations that are both crucial to accurate modeling of materials where temperature and pressure effects are influential.

Carbon phosphide monolayers with superior carrier mobility

NASA Astrophysics Data System (ADS)

Wang, Gaoxue; Pandey, Ravindra; Karna, Shashi P.

2016-04-01

Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of the carbon phosphide (CP) monolayer consisting of sp2 hybridized C atoms and sp3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as α-CP and β-CP with puckered or buckled surfaces are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have the lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The γ-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest that the binary CP monolayer is a yet unexplored 2D material holding great promise for applications in high-performance electronics and optoelectronics.Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of the carbon phosphide (CP) monolayer consisting of sp2 hybridized C atoms and sp3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as α-CP and β-CP with puckered or buckled surfaces are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have the lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The γ-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest that the binary CP monolayer is a yet unexplored 2D material holding great promise for applications in high-performance electronics and optoelectronics. Electronic supplementary information (ESI) available: Fig. S1 cohesive energy and structure of the CP monolayer with various stoichiometric compositions obtained using CALYPSO, Fig. S2 history of CALYPSO steps and structure of the CP monolayer, Fig. S3 phonon dispersion with DFT-D2 functional, Fig. S4 band structure for β-CP using the DFT-PBE and DFT-D2 functional forms, Fig. S5 strain energy curves, Fig. S6 projected band structure for α-CP, Fig. S7 projected band structure for β-CP, Fig. S8 projected band structure for γ-CP, Fig. S9 band structures obtained with the GGA-PBE and HSE06 functional; Table S1 lattice parameters with the DFT-D2 functional form; Video S1 AIMD simulation of α-CP at 300 K, Video S2 AIMD simulation of β-CP at 300 K, Video S3 AIMD simulation of γ-CP at 300 K. See DOI: 10.1039/c6nr00498a

Molecular interactions in the complexes of toluene with butyronitrile: A DFT approach

NASA Astrophysics Data System (ADS)

Karthick, N. K.; Arivazhagan, G.

2018-04-01

Density Functional Theory (DFT) has been employed to investigate the self association of butyronitrile and the heterointeractions in the 1:2 (toluene: butyronitrile) and 1:1 complexes of toluene with butyronitrile. For this investigation the B3LYP functional with Grimme's dispersion correction (D3) term and ωB97XD functionals were used. The theoretical frequency analysis shows the unsuitability of B3LYP with D3 for the present investigation. Therefore, Natural Bonding Orbital analysis was done at the functional ωB97XD. It is found through this work that only the methylene hydrogens of butyronitrile are responsible for the self association among the butyronitrile molecules. In 1:1 complex, the red shift in the butyronitrile methyl asymmetric stretching mode is not due to the active participation of this group in heterointeractions and it is solely due to the other interactions happening in its vicinity. Only the interaction (TOL) C - H ⋯ N(BN) is present in the complex. In 1:2 complex the butyronitrile methyl/methylene hydrogens interact with the delocalized electron cloud of toluene and the toluene hydrogens interact with the butyronitrile nitrogen. Comparison of interaction energies shows that the stability of 1:2 complex is more than that of butyronitrile dimer and 1:1 complex.

Effect of oxygen vacancies on the electronic and optical properties of tungsten oxide from first principles calculations

NASA Astrophysics Data System (ADS)

Mehmood, Faisal; Pachter, Ruth; Murphy, Neil R.; Johnson, Walter E.; Ramana, Chintalapalle V.

2016-12-01

In this work, we investigated theoretically the role of oxygen vacancies on the electronic and optical properties of cubic, γ-monoclinic, and tetragonal phases of tungsten oxide (WO3) thin films. Following the examination of structural properties and stability of the bulk tungsten oxide polymorphs, we analyzed band structures and optical properties, applying density functional theory (DFT) and GW (Green's (G) function approximation with screened Coulomb interaction (W)) methods. Careful benchmarking of calculated band gaps demonstrated the importance of using a range-separated functional, where results for the pristine room temperature γ-monoclinic structure indicated agreement with experiment. Further, modulation of the band gap for WO3 structures with oxygen vacancies was quantified. Dielectric functions for cubic WO3, calculated at both the single-particle, essentially time-dependent DFT, as well as many-body GW-Bethe-Salpeter equation levels, indicated agreement with experimental data for pristine WO3. Interestingly, we found that introducing oxygen vacancies caused appearance of lower energy absorptions. A smaller refractive index was indicated in the defective WO3 structures. These predictions could lead to further experiments aimed at tuning the optical properties of WO3 by introducing oxygen vacancies, particularly for the lower energy spectral region.

Excitons and Davydov splitting in sexithiophene from first-principles many-body Green's function theory

NASA Astrophysics Data System (ADS)

Leng, Xia; Yin, Huabing; Liang, Dongmei; Ma, Yuchen

2015-09-01

Organic semiconductors have promising and broad applications in optoelectronics. Understanding their electronic excited states is important to help us control their spectroscopic properties and performance of devices. There have been a large amount of experimental investigations on spectroscopies of organic semiconductors, but theoretical calculation from first principles on this respect is still limited. Here, we use density functional theory (DFT) and many-body Green's function theory, which includes the GW method and Bethe-Salpeter equation, to study the electronic excited-state properties and spectroscopies of one prototypical organic semiconductor, sexithiophene. The exciton energies of sexithiophene in both the gas and bulk crystalline phases are very sensitive to the exchange-correlation functionals used in DFT for ground-state structure relaxation. We investigated the influence of dynamical screening in the electron-hole interaction on exciton energies, which is found to be very pronounced for triplet excitons and has to be taken into account in first principles calculations. In the sexithiophene single crystal, the energy of the lowest triplet exciton is close to half the energy of the lowest singlet one. While lower-energy singlet and triplet excitons are intramolecular Frenkel excitons, higher-energy excitons are of intermolecular charge-transfer type. The calculated optical absorption spectra and Davydov splitting are in good agreement with experiments.

Structure and Electronic Properties of Neutral and Negatively Charged RhBn Clusters (n = 3-10): A Density Functional Theory Study.

PubMed

Li, Peifang; Mei, Tingting; Lv, Linxia; Lu, Cheng; Wang, Weihua; Bao, Gang; Gutsev, Gennady L

2017-08-31

The geometrical structure and electronic properties of the neutral RhB n and singly negatively charged RhB n - clusters are obtained in the range of 3 ≤ n ≤ 10 using the unbiased CALYPSO structure search method and density functional theory (DFT). A combination of the PBE0 functional and the def2-TZVP basis set is used for determining global minima on potential energy surfaces of the Rh-doped B n clusters. The photoelectron spectra of the anions are simulated using the time-dependent density functional theory (TD-DFT) method. Good agreement between our simulated and experimentally obtained photoelectron spectra for RhB 9 - provides support to the validity of our theoretical method. The relative stabilities of the ground-state RhB n and RhB n - clusters are estimated using the calculated binding energies, second-order total energy differences, and HOMO-LUMO gaps. It is found that RhB 7 and RhB 8 - are the most stable species in the neutral and anionic series, respectively. The chemical bonding analysis reveals that the RhB 8 - cluster possesses two sets of delocalized σ and π bonds. In both cases, the Hückel 4N + 2 rule is fulfilled and this cluster possesses both σ and π aromaticities.

Excited State Studies of Polyacenes Using the All-Order Constricted Variational Density Functional Theory with Orbital Relaxation.

PubMed

Senn, Florian; Krykunov, Mykhaylo

2015-10-22

For the polyacenes series from naphthalene to hexacene, we present the vertical singlet excitation energies 1 (1)La and 1 (1)Lb, as well as the first triplet excitation energies obtained by the all-order constricted variational density functional theory with orbital relaxation (R-CV(∞)-DFT). R-CV(∞)-DFT is a further development of variational density functional theory (CV(∞)-DFT), which has already been successfully applied for the calculation of the vertical singlet excitation energies (1)La and (1)Lb for polyacenes,15 and we show that one obtains consistent excitation energies using the local density approximation as a functional for singlet as well as for triplet excitations when going beyond the linear response theory. Furthermore, we apply self-consistent field density functional theory (ΔSCF-DFT) and compare the obtained excitation energies for the first triplet excitations T1, where, due to the character of the transition, ΔSCF-DFT and R-CV(∞)-DFT become numerically equivalent, and for the singlet excitations 1 (1)La and 1 (1)Lb, where the two methods differ.

Molecular Spintronics: Theory of Spin-Dependent Electron Transport in Fe/BDT/Fe Molecular Wire Systems

NASA Astrophysics Data System (ADS)

Dalgleish, Hugh; Kirczenow, George

2004-03-01

Metal/Molecule/Metal junction systems forming molecular wires are currently the focus of intense study. Recently, spin-dependent electron transport in molecular wires with magnetic Ni electrodes has been studied theoretically, and spin-valve effects have been predicted.* Here we explore theoretically another magnetic molecular wire system, namely, ferromagnetic Fe nano-contacts bridged with 1,4-benzene-dithiolate (BDT). We estimate the essential structural and electronic parameters for this system based on ab initio density functional calculations (DFT) for some simple model systems involving thiol groups and Fe clusters as well as semi-empirical considerations and the known electronic structure of bulk Fe. We then use Lippmann-Schwinger and Green's function techniques together with the Landauer formalism to study spin-dependent transport. *E. G. Emberly and G. Kirczenow, Chem. Phys. 281, 311 (2002); R. Pati, L. Senapati, P.M. Ajayan and S.K. Nayak, Phys. Rev. B68, 100407 (2003).

Experimental and theoretical study on DPPH radical scavenging mechanism of some chalcone quinoline derivatives

NASA Astrophysics Data System (ADS)

Hamlaoui, Ikram; Bencheraiet, Reguia; Bensegueni, Rafik; Bencharif, Mustapha

2018-03-01

In this study, the antioxidant capacity of three chalcone derivatives was evaluated by DPPH free radical scavenging. Experimental data showed low antioxidant activity (IC50±SD) of these molecules in comparison with BHT. The mechanism of DPPH radical scavenging elucidated by means of density functional theory (DFT) calculations. The tested compounds and their corresponding radicals and anions were optimized using B3LYP functional with 6-31G (d,p) basis set in the gas phase. The C-PCM model was used to perform solvent medium calculations. On the basis of theoretical calculations, it was shown that HAT mechanism was predominant in the gas phase, whereas SET-PT and SPLET mechanisms were favored in the presence of the solvent. Moreover, the HOMO orbitals and spin density distribution was evaluated to predict the probable sites for free radical attack.

Synthesis, structural characterization and theoretical studies of a new Schiff base 4-(((3-(tert-Butyl)-(1-phenyl)pyrazol-5-yl) imino)methyl)phenol

NASA Astrophysics Data System (ADS)

Cuenú, Fernando; Londoño-Salazar, Jennifer; Torres, John Eduard; Abonia, Rodrigo; D'Vries, Richard F.

2018-01-01

4-(((3-(tert-Butyl)-(1-phenyl)pyrazol-5-yl)imino)methyl)phenol (4-OHFPz) was synthesized and characterized by FT-IR, MS, NMR, and single-crystal X-ray diffraction. Optimization of molecular geometry, vibrational frequencies, and chemical shifts were calculated by using the methods of density functional theory (DFT) with B3LYP and B3PW91 as functionals and Hartree-Fock with 6-311G++(d,p) as basis set using the GAUSSIAN 09 program package. With the VEDA 4 software, the vibrational frequencies were assigned in terms of the potential energy distribution (PED). The equilibrium geometries calculated by all methods were compared with X-ray diffraction results, indicating that the theoretical results matches well with the experimental ones. The data obtained from the vibrational analysis and the calculated NMR are consistent with the experimental spectra.

The structure elucidation of mequindox and 1,4-bisdesoxymequindox: NMR analyses, FT-IR spectra, DFT calculations and thermochemical studies

NASA Astrophysics Data System (ADS)

Zhang, Jiaheng; He, Xin; Gao, Haixiang

2011-10-01

In the current work, we report a combined experimental and theoretical study on the molecular conformation, vibrational spectra, and nuclear magnetic resonance (NMR) spectra of mequindox (MEQ) and 1,4-bisdesoxymequindox (1,4-BDM). The geometric structure and vibrational frequencies of MEQ and 1,4-BDM have been calculated by density functional theory employing the B3LYP functional and 6-311++G(d,p) basis set. The 1H and 13C NMR chemical shifts have been calculated by gauge-including atomic orbital method with B3LYP 6-311++G(2df,2pd) approach. The calculation results have been applied to simulate the infrared and NMR spectra of the compounds. The theoretical results agree well with the observed spectra. The bond dissociation enthalpy of MEQ and the heat of formation of MEQ and 1,4-BDM have also been computed.

Synthesis, spectroscopic characterization and quantum chemical computational studies of (S)-N-benzyl-1-phenyl-5-(pyridin-2-yl)-pent-4-yn-2-amine

NASA Astrophysics Data System (ADS)

Kose, Etem; Atac, Ahmet; Karabacak, Mehmet; Karaca, Caglar; Eskici, Mustafa; Karanfil, Abdullah

2012-11-01

The synthesis and characterization of a novel compound (S)-N-benzyl-1-phenyl-5-(pyridin-2-yl)-pent-4-yn-2-amine (abbreviated as BPPPYA) was presented in this study. The spectroscopic properties of the compound were investigated by FT-IR, NMR and UV spectroscopy experimentally and theoretically. The molecular geometry and vibrational frequencies of the BPPPYA in the ground state were calculated by using density functional theory (DFT) B3LYP method invoking 6-311++G(d,p) basis set. The geometry of the BPPPYA was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. The results of the energy and oscillator strength calculated by time-dependent density functional theory (TD-DFT) and CIS approach complement with the experimental findings. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis were presented. The theoretical NMR chemical shifts (1H and 13C) complement with experimentally measured ones. The dipole moment, linear polarizability and first hyperpolarizability values were also computed. The linear polarizabilities and first hyper polarizabilities of the studied molecule indicate that the compound is a good candidate of nonlinear optical materials. The calculated vibrational wavenumbers, absorption wavelengths and chemical shifts showed the best agreement with the experimental results.

Assessment of amide I spectroscopic maps for a gas-phase peptide using IR-UV double-resonance spectroscopy and density functional theory calculations

NASA Astrophysics Data System (ADS)

Carr, J. K.; Zabuga, A. V.; Roy, S.; Rizzo, T. R.; Skinner, J. L.

2014-06-01

The spectroscopy of amide I vibrations has become a powerful tool for exploring protein structure and dynamics. To help with spectral interpretation, it is often useful to perform molecular dynamics (MD) simulations. To connect spectroscopic experiments to simulations in an efficient manner, several researchers have proposed "maps," which relate observables in classical MD simulations to quantum spectroscopic variables. It can be difficult to discern whether errors in the theoretical results (compared to experiment) arise from inaccuracies in the MD trajectories or in the maps themselves. In this work, we evaluate spectroscopic maps independently from MD simulations by comparing experimental and theoretical spectra for a single conformation of the α-helical model peptide Ac-Phe-(Ala)5-Lys-H+ in the gas phase. Conformation-specific experimental spectra are obtained for the unlabeled peptide and for several singly and doubly 13C-labeled variants using infrared-ultraviolet double-resonance spectroscopy, and these spectra are found to be well-modeled by density functional theory (DFT) calculations at the B3LYP/6-31G** level. We then compare DFT results for the deuterated and 13C18O-labeled peptide with those from spectroscopic maps developed and used previously by the Skinner group. We find that the maps are typically accurate to within a few cm-1 for both frequencies and couplings, having larger errors only for the frequencies of terminal amides.

Assessment of amide I spectroscopic maps for a gas-phase peptide using IR-UV double-resonance spectroscopy and density functional theory calculations

PubMed Central

Carr, J. K.; Zabuga, A. V.; Roy, S.; Rizzo, T. R.; Skinner, J. L.

2014-01-01

The spectroscopy of amide I vibrations has become a powerful tool for exploring protein structure and dynamics. To help with spectral interpretation, it is often useful to perform molecular dynamics (MD) simulations. To connect spectroscopic experiments to simulations in an efficient manner, several researchers have proposed “maps,” which relate observables in classical MD simulations to quantum spectroscopic variables. It can be difficult to discern whether errors in the theoretical results (compared to experiment) arise from inaccuracies in the MD trajectories or in the maps themselves. In this work, we evaluate spectroscopic maps independently from MD simulations by comparing experimental and theoretical spectra for a single conformation of the α-helical model peptide Ac-Phe-(Ala)5-Lys-H+ in the gas phase. Conformation-specific experimental spectra are obtained for the unlabeled peptide and for several singly and doubly 13C-labeled variants using infrared-ultraviolet double-resonance spectroscopy, and these spectra are found to be well-modeled by density functional theory (DFT) calculations at the B3LYP/6-31G** level. We then compare DFT results for the deuterated and 13C18O-labeled peptide with those from spectroscopic maps developed and used previously by the Skinner group. We find that the maps are typically accurate to within a few cm−1 for both frequencies and couplings, having larger errors only for the frequencies of terminal amides. PMID:24929378

Vibrational spectroscopic studies and DFT calculations of 4-aminoantipyrine

NASA Astrophysics Data System (ADS)

Swaminathan, J.; Ramalingam, M.; Sethuraman, V.; Sundaraganesan, N.; Sebastian, S.

2009-08-01

The pyrazole derivative, 4-aminoantipyrine (4AAP), used as an intermediate for the synthesis of pharmaceuticals especially antipyretic and analgesic drugs has been analyzed experimentally and theoretically for its vibrational frequencies. The FTIR and FT Raman spectra of the title compound have been compared with the theoretically computed frequencies invoking the standard 6-311g(d,p) and cc-pVDZ basis sets at DFT level of theory (B3LYP). The harmonic vibrational frequencies at B3LYP/cc-pVDZ after appropriate scaling method seem to coincide satisfactorily with the experimental observations rather than B3LYP/6-311g(d,p) results. The theoretical spectrograms for FT-IR and FT-Raman spectra of 4AAP have been also constructed and compared with the experimental spectra. Additionally, thermodynamic data have also been calculated and discussed.

On the calculation of charge transfer transitions with standard density functionals using constrained variational density functional theory.

PubMed

Ziegler, Tom; Krykunov, Mykhaylo

2010-08-21

It is well known that time-dependent density functional theory (TD-DFT) based on standard gradient corrected functionals affords both a quantitative and qualitative incorrect picture of charge transfer transitions between two spatially separated regions. It is shown here that the well known failure can be traced back to the use of linear response theory. Further, it is demonstrated that the inclusion of higher order terms readily affords a qualitatively correct picture even for simple functionals based on the local density approximation. The inclusion of these terms is done within the framework of a newly developed variational approach to excitation energies called constrained variational density functional theory (CV-DFT). To second order [CV(2)-DFT] this theory is identical to adiabatic TD-DFT within the Tamm-Dancoff approximation. With inclusion of fourth order corrections [CV(4)-DFT] it affords a qualitative correct description of charge transfer transitions. It is finally demonstrated that the relaxation of the ground state Kohn-Sham orbitals to first order in response to the change in density on excitation together with CV(4)-DFT affords charge transfer excitations in good agreement with experiment. The new relaxed theory is termed R-CV(4)-DFT. The relaxed scheme represents an effective way in which to introduce double replacements into the description of single electron excitations, something that would otherwise require a frequency dependent kernel.

Structures and electronic states of halogen-terminated graphene nano-flakes

NASA Astrophysics Data System (ADS)

Tachikawa, Hiroto; Iyama, Tetsuji

2015-12-01

Halogen-functionalized graphenes are utilized as electronic devices and energy materials. In the present paper, the effects of halogen-termination of graphene edge on the structures and electronic states of graphene flakes have been investigated by means of density functional theory (DFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the halogen termination, while the excitation energy is red-shifted. The drastic change showed a possibility as electronic devices such as field-effect transistors. The change of electronic states caused by the halogen termination of graphene edge was discussed on the basis of the theoretical results.

Structure and stability of complexes of agmatine with some functional receptor residues of proteins

NASA Astrophysics Data System (ADS)

Remko, Milan; Broer, Ria; Remková, Anna; Van Duijnen, Piet Th.

2017-04-01

The paper reports the results of a theoretical study of the conformational behavior and basicity of biogenic amine agmatine. The complexes modelling of agmatine - protein interaction are also under scrutiny of our investigation using the Becke3LYP and B97D levels of the density functional theory. The relative stabilities (Gibbs energies) of individual complexes are by both DFT methods described equally. Hydration has a dramatic effect on the hydrogen bonded complexes studied. The pairing acidic carboxylate group with different agmatine species resulted in charged hydrogen bond complexes containing negatively charged acetate species acting as proton acceptors.

Influence of water on the surface of graphene

NASA Astrophysics Data System (ADS)

Kaya, Yunus; Kalkan, Yalçin; Veenhof, Rob

2018-02-01

We have studied how water modifies the surface of graphene and in particular how the surface conductivity of graphene is affected. According to the literature, two types of interactions should be distinguished: physical, where a water molecule remains intact and is located at some distance from the mesh, and chemical, where a water molecule is imbricated in the graphene bond structure. We have developed theoretical models for both types of interactions using the density functional theory (DFT) with the B3LYP hybrid functional combined with the 6-31G(d) basis set. Our calculations show that the surface conductivity of graphene is reduced in the presence of water.

Experimental and theoretical study on THz spectrum artesunate

NASA Astrophysics Data System (ADS)

Zhang, Ai-Bing; Kong, Ling-Gao; Wang, Shi-Jin; Li, Lei; Zheng, Xiang-Zhi

2008-10-01

Artesunate is a very effective drug to treat malaria. They are studied experimentally by Terahertz (THz) time-domain spectroscopy (THz-TDS), and the characteristic absorption spectra are obtained in the range of 0.2 to 2.6 THz. The vibrational frequencies are calculated using the density functional theory (DFT). Theoretical results show that 0.71, 1.94 and 2.46 THz are significant agreement with the experimental results in 0.87, 1.82 and 2.46THz, and identification of vibrational modes are given. The calculated results further confirm that the characteristic frequencies come from the collective vibrational modes. The results suggest that the use of the THz-TDS technique can be an effective way to inspect for Chinese medicine.

Conformational, spectroscopic and nonlinear optical properties of biologically active N,N-dimethyltryptamine molecule: A theoretical study

NASA Astrophysics Data System (ADS)

Öner, Nazmiye; Tamer, Ömer; Avcı, Davut; Atalay, Yusuf

2014-12-01

The effective psychoactive properties of N,N-dimethyltryptamine (DMT) known as the near-death molecule have encouraged the imagination of many research disciplines for several decades. Although there is no theoretical study, a number of paper composed by experimental techniques have been reported for DMT molecule. In this study, the molecular modeling of DMT was carried out using B3LYP and HSEh1PBE levels of density functional theory (DFT). Our calculations showed that the energy gap between HOMO and LUMO is low, demonstrating that DMT is a biologically active molecule. Large hyperconjugation interaction energies imply that molecular charge transfer occurs in DMT. Moreover, NLO analysis indicates that DMT can be used an effective NLO material.

Experimental and theoretical studies of a pyrazole-thiazolidin-2,4-di-one hybrid

NASA Astrophysics Data System (ADS)

Mushtaque, Md.; Avecilla, Fernando; Haque, Ashanul; Perwez, Ahmad; Khan, Md. Shahzad; Rizvi, M. Moshahid Alam

2017-08-01

The present work describes synthesis, characterization and biological evaluations of a hybrid compound 10 composed of two intriguing scaffolds pyrazole and thiazolidin-2,4-di-one. The title compound was obtained via multi-step reaction and characterized by a number of techniques (viz. IR, UV-Visible, 1H-NMR, 13C-NMR and MS) including X-ray crystallography. The structural and photophysical data of compound 10 were well supported by theoretical calculations performed at density functional (DFT) level. In-vitro anticancer studies on different human cancer cell lines indicated moderate to low activity of the compounds. The molecular target of the compound was predicted through in-silico studies. Finding of the studies are presented herein.

QSAR, DFT and quantum chemical studies on the inhibition potentials of some carbozones for the corrosion of mild steel in HCl.

PubMed

Eddy, Nnabuk O; Ita, Benedict I

2011-02-01

Experimental aspects of the inhibition of the corrosion of mild steel in HCl solutions by some carbozones were studied using gravimetric, thermometric and gasometric methods, while a theoretical study was carried out using density functional theory, a quantitative structure-activity relation, and quantum chemical principles. The results obtained indicated that the studied carbozones are good adsorption inhibitors for the corrosion of mild steel in HCl. The inhibition efficiencies of the studied carbozones were found to increase with increasing concentration of the respective inhibitor. A strong correlation was found between the average inhibition efficiency and some quantum chemical parameters, and also between the experimental and theoretical inhibition efficiencies (obtained from the quantitative structure-activity relation).

FT-IR, FT-Raman, and DFT computational studies of melaminium nitrate molecular-ionic crystal

NASA Astrophysics Data System (ADS)

Tanak, Hasan; Marchewka, Mariusz K.

2013-02-01

The experimental and theoretical vibrational spectra of melaminium nitrate were studied. The Raman and infrared (FT-IR) spectra of the melaminium nitrate and its deuterated analogue were recorded in the solid phase. Molecular geometry and vibrational frequency values of melaminium nitrate in the electronic ground state were calculated using the density functional method (B3LYP) with the 6-31++G(d,p) basis set. The calculated results show that the optimized geometry can well reproduce the crystal structure, and the theoretical vibrational frequency values show good agreement with experimental values. The NBO analysis reveals that the N-H···O and N-H···N intermolecular interactions significantly influence crystal packing in this molecule.

Density functional theory across chemistry, physics and biology.

PubMed

van Mourik, Tanja; Bühl, Michael; Gaigeot, Marie-Pierre

2014-03-13

The past decades have seen density functional theory (DFT) evolve from a rising star in computational quantum chemistry to one of its major players. This Theme Issue, which comes half a century after the publication of the Hohenberg-Kohn theorems that laid the foundations of modern DFT, reviews progress and challenges in present-day DFT research. Rather than trying to be comprehensive, this Theme Issue attempts to give a flavour of selected aspects of DFT.

FT-IR, FT-Raman, UV spectra and DFT calculations on monomeric and dimeric structure of 2-amino-5-bromobenzoic acid.

PubMed

Karabacak, Mehmet; Cinar, Mehmet

2012-02-01

In this work, the molecular conformation, vibrational and electronic transition analysis of 2-amino-5-bromobenzoic acid (2A5BrBA) were presented for the ground state using experimental techniques (FT-IR, FT-Raman and UV) and density functional theory (DFT) employing B3LYP exchange correlation with the 6-311++G(d,p) basis set. FT-IR and FT-Raman spectra were recorded in the regions of 400-4000 cm(-1) and 50-4000 cm(-1), respectively. There are four conformers, C1, C2, C3 and C4 for this molecule. The geometrical parameters, energies and wavenumbers have been obtained for all four conformers. The computational results diagnose the most stable conformer of 2A5BrBA as the C1 form. The complete assignments of fundamental vibrations were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Raman activities calculated by DFT method have been converted to the corresponding Raman intensities using Raman scattering theory. The UV spectra of investigated compound were recorded in the region of 200-400 nm for ethanol and water solutions. The electronic properties were evaluated with help of time-dependent DFT (TD-DFT) theoretically and results were compared with experimental observations. The thermodynamic properties of the studied compound at different temperatures were calculated, revealing the correlations between standard heat capacity, standard entropy, standard enthalpy changes and temperatures. The observed and the calculated geometric parameters, vibrational wavenumbers and electronic transitions were compared with observed data and found to be in good agreement. Copyright © 2011 Elsevier B.V. All rights reserved.

Gas-phase reactions of uranate ions, UO(2)(-), UO(3)(-), UO(4)(-), and UO(4)H(-), with methanol: a convergence of experiment and theory.

PubMed

Michelini, Maria Del Carmen; Marçalo, Joaquim; Russo, Nino; Gibson, John K

2010-04-19

Bimolecular reactions of uranium oxide molecular anions with methanol have been studied experimentally, by Fourier transform ion cyclotron resonance mass spectrometry, and computationally, by density functional theory (DFT). The primary goals were to provide fundamental insights into mechanistic and structural details of model reactions of uranium oxides with organics, and to examine the validity of theoretical modeling of these types of reactions. The ions UO(3)(-), UO(4)(-), and UO(4)H(-) each reacted with methanol to give a singular product; the primary products each exhibited sequential reactions with two additional methanol molecules to again give singular products. The observed reactions were elimination of water, formaldehyde, or hydrogen, and in one case addition of a methanol molecule. The potential energy profiles were computed for each reaction, and isotopic labeling experiments were performed to probe the validity of the computed mechanisms and structures-in each case where the experiments could be compared with the theory there was concurrence, clearly establishing the efficacy of the employed DFT methodologies for these and related reaction systems. The DFT results were furthermore in accord with the surprisingly inert nature of UO(2)(-). The results provide a basis to understand mechanisms of key reactions of uranium oxides with organics, and a foundation to extend DFT methodologies to more complex actinide systems which are not amenable to such direct experimental studies.

A combined TD-DFT and spectroscopic investigation of the solute-solvent interactions of efavirenz

NASA Astrophysics Data System (ADS)

Jordaan, Maryam A.; Singh, Parvesh; Martincigh, Bice S.

2016-03-01

Efavirenz, commercially known as Sustiva® or Stocrin®, is a first-line antiretroviral treatment for HIV/AIDS. The clinical efficacy of efavirenz is, however, hindered by its solubility. We sought to investigate the solute-solvent effects of efavirenz by means of a combined qualitative study implementing UV-visible spectrophotometry, 1H NMR spectroscopy and time-dependent density functional theory (TD-DFT) calculations. The UV spectrum displayed two main absorbance maxima, band I and band II at 246-260 and 291-295 nm, respectively. A general bathochromic shift was noticed from the non-polar solvent cyclohexane to the most polar solvent DMSO (≈ 13.69 nm) in band I and a smaller bathochromic (≈ 2.17 nm) and hyperchromic shift was observed in band II. We propose that these observations are due to the role of the amino (NH) and carbonyl (CO) functionalities which induce charge-transfer and intra- and inter-molecular hydrogen bonding. The aromatic and amine protons showed the most deshielded effects in the observed chemical shifts (δ) in the more polar DMSO-d6 solvent relative to CDCl3. The 1H NMR chemical shifts observed are due to the increased delocalization of the lone pair electrons of the amino nitrogen with increased polarity of the more polar DMSO solvent. The theoretical reproduction of the UV and 1H NMR spectra by means of TD-DFT is in good agreement with the experimental results.

Electronic structure, hydrogen bonding and spectroscopic profile of a new 1,2,4-triazole-5(4H)-thione derivative: A combined experimental and theoretical (DFT) analysis

NASA Astrophysics Data System (ADS)

Al-Tamimi, Abdul-Malek S.

2016-09-01

Density functional theory has been implemented to study the electronic structure, molecular properties and vibrational spectra of 3-(adamantan-1-yl)-4-(4-chlorophenyl)-1H-1,2,4-triazole-5(4H)-thione, a novel 1,2,4-triazole-5(4H)-thione derivative. Hydrogen bonded dimer of the title molecule has been studied using B3LYP, M06-2X and X3LYP functionals at 6-311++ G(d,p) level of theory. The intermolecular hydrogen bonding has been studied using NBO analysis of the dimer. Bader's AIM theory was also used to evaluate the strength as well as the hydrogen bonding characteristics. Experimental FT-IR and FT-Raman spectra of the title molecule were related with the spectral data obtained with DFT/B3LYP method. The 1H NMR chemical shifts of the title molecule were calculated by the GIAO method and compared with experimental results. Dipole moment, polarizability (α), first order static hyperpolarizability (β) along with molecular electrostatic potential surface have been calculated. Frequency-dependent first hyperpolarizabilities, β(-2ω;ω,ω) and β(-ω;ω,0) have also been evaluated to study the non-linear optical behavior of the title compound. UV-Vis spectrum of the title molecule was recorded and TD-DFT method has been used to calculate six lowest excited states and the corresponding excitation energies.

Spectroscopic and density functional theory studies of 5,7,3',5'-tetrahydroxyflavanone from the leaves of Olea ferruginea.

PubMed

Hashmi, Muhammad Ali; Khan, Afsar; Ayub, Khurshid; Farooq, Umar

2014-07-15

5,7,3',5'-Tetrahydroxyflavanone (1) was isolated from the leaves of Olea ferruginea and a theoretical model was developed for obtaining the electronic and spectroscopic properties of 1. The geometric and electronic properties were calculated at B3LYP/6-311 G (d, p) level of Density Functional Theory (DFT). The theoretical data was in good agreement with the experimental one. The optimized geometric parameters of compound 1 were calculated for the first time. The theoretical vibrational frequencies of 1 were found to correlate with the experimental IR spectrum after a scaling factor of 0.9811. The UV and NMR spectral data computed theoretically were in good agreement with the experimental data. Electronic properties of the compound i.e., ionization potential (IP), electron affinity (EA), coefficients of HOMO and LUMO were estimated computationally for the first time which can be used to explain its antioxidant as well as other related activities and more active sites on it. The intermolecular interactions and their effects on IR frequencies, electronic and geometric parameters were simulated using water molecule as a model for hydrogen bonding with flavonoid hydroxyl groups. Copyright © 2014 Elsevier B.V. All rights reserved.

Spectroscopic and density functional theory studies of 5,7,3‧,5‧-tetrahydroxyflavanone from the leaves of Olea ferruginea

NASA Astrophysics Data System (ADS)

Hashmi, Muhammad Ali; Khan, Afsar; Ayub, Khurshid; Farooq, Umar

2014-07-01

5,7,3‧,5‧-Tetrahydroxyflavanone (1) was isolated from the leaves of Olea ferruginea and a theoretical model was developed for obtaining the electronic and spectroscopic properties of 1. The geometric and electronic properties were calculated at B3LYP/6-311 G (d, p) level of Density Functional Theory (DFT). The theoretical data was in good agreement with the experimental one. The optimized geometric parameters of compound 1 were calculated for the first time. The theoretical vibrational frequencies of 1 were found to correlate with the experimental IR spectrum after a scaling factor of 0.9811. The UV and NMR spectral data computed theoretically were in good agreement with the experimental data. Electronic properties of the compound i.e., ionization potential (IP), electron affinity (EA), coefficients of HOMO and LUMO were estimated computationally for the first time which can be used to explain its antioxidant as well as other related activities and more active sites on it. The intermolecular interactions and their effects on IR frequencies, electronic and geometric parameters were simulated using water molecule as a model for hydrogen bonding with flavonoid hydroxyl groups.

SbCl3-catalyzed one-pot synthesis of 4,4′-diaminotriarylmethanes under solvent-free conditions: Synthesis, characterization, and DFT studies

PubMed Central

2011-01-01

Summary A simple, efficient, and mild procedure for a solvent-free one-step synthesis of various 4,4′-diaminotriarylmethane derivatives in the presence of antimony trichloride as catalyst is described. Triarylmethane derivatives were prepared in good to excellent yields and characterized by elemental analysis, FTIR, 1H and 13C NMR spectroscopic techniques. The structural and vibrational analysis were investigated by performing theoretical calculations at the HF and DFT levels of theory by standard 6-31G*, 6-31G*/B3LYP, and B3LYP/cc-pVDZ methods and good agreement was obtained between experimental and theoretical results. PMID:21445373

Evaluation of exchange-correlation functionals for time-dependent density functional theory calculations on metal complexes.

PubMed

Holland, Jason P; Green, Jennifer C

2010-04-15

The electronic absorption spectra of a range of copper and zinc complexes have been simulated by using time-dependent density functional theory (TD-DFT) calculations implemented in Gaussian03. In total, 41 exchange-correlation (XC) functionals including first-, second-, and third-generation (meta-generalized gradient approximation) DFT methods were compared in their ability to predict the experimental electronic absorption spectra. Both pure and hybrid DFT methods were tested and differences between restricted and unrestricted calculations were also investigated by comparison of analogous neutral zinc(II) and copper(II) complexes. TD-DFT calculated spectra were optimized with respect to the experimental electronic absorption spectra by use of a Matlab script. Direct comparison of the performance of each XC functional was achieved both qualitatively and quantitatively by comparison of optimized half-band widths, root-mean-squared errors (RMSE), energy scaling factors (epsilon(SF)), and overall quality-of-fit (Q(F)) parameters. Hybrid DFT methods were found to outperform all pure DFT functionals with B1LYP, B97-2, B97-1, X3LYP, and B98 functionals providing the highest quantitative and qualitative accuracy in both restricted and unrestricted systems. Of the functionals tested, B1LYP gave the most accurate results with both average RMSE and overall Q(F) < 3.5% and epsilon(SF) values close to unity (>0.990) for the copper complexes. The XC functional performance in spin-restricted TD-DFT calculations on the zinc complexes was found to be slightly worse. PBE1PBE, mPW1PW91 and B1LYP gave the most accurate results with typical RMSE and Q(F) values between 5.3 and 7.3%, and epsilon(SF) around 0.930. These studies illustrate the power of modern TD-DFT calculations for exploring excited state transitions of metal complexes. 2009 Wiley Periodicals, Inc.

Crystal structure, vibrational, spectral investigation, quantum chemical DFT calculations and thermal behavior of Diethyl [hydroxy (phenyl) methyl] phosphonate

NASA Astrophysics Data System (ADS)

Ouksel, Louiza; Chafaa, Salah; Bourzami, Riadh; Hamdouni, Noudjoud; Sebais, Miloud; Chafai, Nadjib

2017-09-01

Single Diethyl [hydroxy (phenyl) methyl] phosphonate (DHPMP) crystal with chemical formula C11H17O4P, was synthesized via the base-catalyzed Pudovik reaction and Lewis acid as catalyst. The results of SXRD analyzes indicate that this compound crystallizes into a mono-clinic system with space group P21/n symmetry and Z = 4. The crystal structure parameters are a = 9.293 Å, b = 8.103 Å, c = 17.542 Å, β = 95.329° and V = 1315.2 Å3, the structure displays one inter-molecular O-H⋯O hydrogen bonding. The UV-Visible absorption spectrum shows that the crystal exhibits a good optical transmission in the visible domain, and strong absorption in middle ultraviolet one. The vibrational frequencies of various functional groups present in DHPMP crystal have been deduced from FT-IR and FT-Raman spectra and then compared with theoretical values performed with DFT (B3LYP) method using 6-31G (p, d) basis sets. Chemical and thermodynamic parameters such as: ionization potential (I), electron affinity (A), hardness (σ), softness (η), electronegativity (χ) and electrophilicity index (ω), are also calculated using the same theoretical method. The thermal decomposition behavior of DHPMP, studied by using thermogravimetric analysis (TDG), shows a thermal stability until to 125 °C.

Molecular structure, vibrational spectra and quantum chemical MP2/DFT studies toward the rational design of hydroxyurea imprinted polymer

NASA Astrophysics Data System (ADS)

Prasad, Bhim Bali; Rai, Garima

2013-03-01

In this study, both experimental and theoretical vibrational spectra of template (hydroxyurea, HU), monomer (N-(4,6-bisacryloyl amino-[1,3,5] triazine-2-yl-)-acryl amide, TAT), and HU-TAT complexes were compared and these were respectively found to be in good agreement. Binding energies of HU, when complexed with different monomers, were computed using second order Moller Plesset theory (MP2) at 6-311++G(d,p) level both in the gas as well as solution phases. HU is an antineoplastic agent extensively being used in the treatment of polycythaemia Vera and thrombocythemia. It is also used to reduce the frequency of painful attacks in sickle cell anemia. It has antiretroviral property in disease like AIDS. All spectral characterizations were made using Density Functional Theory (DFT) at B3LYP employing 6-31+g(2d, 2p) basis set. The theoretical values for 13C and 1H NMR chemical shifts were found to be in accordance with the corresponding experimental values. Of all different monomers studied for the synthesis of molecularly imprinted polymer (MIP) systems, the monomer TAT (2 mol) was typically found to have a best binding score requisite for complexation with HU (1 mol) at the ground state.

Structural investigation of the cocrystal formed between 5-fluorocytosine and fumaric acid based on vibrational spectroscopic technique.

PubMed

Du, Yong; Cai, Qiang; Xue, Jiadan; Zhang, Qi; Qin, Dan

2017-05-05

The vibrational spectra of 5-fluorocytosine, fumaric acid and their cocrystal were measured using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. Experimental THz results show that the cocrystal has distinct fingerprint spectra in terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.61 and 0.91THz. These are quite different from corresponding raw starting materials. Raman spectra also show similar results about differences between the cocrystal and corresponding raw starting materials. Density functional theory (DFT) was used to simulate the structure of the possible salt form and the cocrystal form between 5-fluorocytosine and fumaric acid. The theoretical terahertz result shows that the cocrystal form has absorption at 0.62 and 0.87THz, which is in agreement with the experimental result. The theoretical Raman result also indicates that the cocrystal form has more possibilities than the salt form. So, it is more reasonable that the structure between 5-fluorocytosine and fumaric acid could be the corresponding cocrystal form. The characteristic bands of the cocrystal between 5-fluorocytosine and fumaric acid are also assigned based on the simulation results from the DFT calculation. Copyright © 2017 Elsevier B.V. All rights reserved.

Spectroscopic investigation on cocrystal formation between adenine and fumaric acid based on infrared and Raman techniques

NASA Astrophysics Data System (ADS)

Du, Yong; Fang, Hong Xia; Zhang, Qi; Zhang, Hui Li; Hong, Zhi

2016-01-01

As an important component of double-stranded DNA, adenine has powerful hydrogen-bond capability, due to rich hydrogen bond donors and acceptors existing within its molecular structure. Therefore, it is easy to form cocrystal between adenine and other small molecules with intermolecular hydrogen-bond effect. In this work, cocrystal of adenine and fumaric acid has been characterized as model system by FT-IR and FT-Raman spectral techniques. The experimental results show that the cocrystal formed between adenine and fumaric acid possesses unique spectroscopical characteristic compared with that of starting materials. Density functional theory (DFT) calculation has been performed to optimize the molecular structures and simulate vibrational modes of adenine, fumaric acid and the corresponding cocrystal. Combining the theoretical and experimental vibrational results, the characteristic bands corresponding to bending and stretching vibrations of amino and carbonyl groups within cocrystal are shifted into lower frequencies upon cocrystal formation, and the corresponding bond lengths show some increase due to the effect of intermolecular hydrogen bonding. Different vibrational modes shown in the experimental spectra have been assigned based on the simulation DFT results. The study could provide experimental and theoretical benchmarks to characterize cocrystal formed between active ingredients and cocrystal formers and also the intermolecular hydrogen-bond effect within cocrystal formation process by vibrational spectroscopic techniques.

Theoretical investigations on the structure and properties of p-n-alkoxy benzoic acid based liquid crystals

NASA Astrophysics Data System (ADS)

Subhapriya, P.; Dhanapal, V.; Sadasivam, K.; Vijayanand, P. S.

2016-05-01

The present study focused on the structural conformations, alkoxy chain lengths and mesogenic properties of two mole of alkoxy benzoic acid(nOBA) and one mole of suberic acid (SA) hydrogen bonded (nOBASA) complexes (n=8 to 10) by density functional theory (DFT) calculations and the Fourier Transform Infrared (FT-IR) spectrum. The intermolecular hydrogen bond formation was confirmed by the optimized geometric bond lengths and bond angles obtained by computation. Using the natural bond orbital (NBO) analysis, the stability of the molecule arising from hyper conjugative interactions and charge delocalization has been analyzed. Results obtained shows that the charge in electron density (ED) in σ*and π* antibonding orbital and second order delocalization energies E(2) authorizes the occurrence of intermolecular charge transfer. The molecular electrostatic potential (MEP) surface map is plotted over the optimized geometry of the molecule to obtain the chemical reactivity of the molecule. From the local charge distributions, the mesomorphic behavior and the nematic phase stabilities for each of the molecule have been predicted. Finally the calculated result is applied to simulated infrared spectra of 8OBASA mesogens which shows good agreement with the observed spectra. The comparison of the theoretical results obtained with the experimental ones shows the reliability of this DFT method.

Spectroscopic characteristic (FT-IR, 1H, 13C NMR and UV-Vis) and theoretical calculations (MEP, DOS, HOMO-LUMO, PES, NBO analysis and keto-enol tautomerism) of new tetradentate N,N‧-bis(4-hydroxysalicylidene)-1,4-phenylenediamine ligand as chelating agent for the synthesis of dinuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes

NASA Astrophysics Data System (ADS)

Rajaei, Iman; Mirsattari, Seyed Nezamoddin

2018-07-01

The synthesis and characterization of a novel symmetrical Schiff base ligand N,Nʹ-bis(4-hydroxysalicylidene)-1,4-phenylenediamine (BHSP) was presented in this study and characterized by FT-IR, NMR (1H and 13C) and UV-Vis spectroscopy experimentally and theoretically. Also a series of binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes of BHSP ligand have been synthesized by conventional sequential route in 1:1 equivalent of L:M ratio and characterized by routine physicochemical characterizations. The molecular geometry and vibrational frequencies of the BHSP in the ground state were calculated by using density functional theory (DFT) B3LYP method invoking 6-31G(d,p) and 6-31++G(d,p) basis sets. To study different conformations of the molecule, potential energy surface (PES) scan investigations were performed. The energetic behavior of the ligand compound (BHSP) in solvent media has been examined using B3LYP method with the 6-31G(d,p) and 6-31++G(d,p) basis sets by applying the polarized continuum model (PCM). In addition, DFT calculations of the BHSP ligand, molecular electrostatic potential (MEP), contour map, natural bond orbital (NBO) analysis, frontier molecular orbitals (FMO) analysis, NMR analysis and TD-DFT calculations were conducted. The calculated properties are in agreement with the available experimental data and closely related molecule BSP. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters.

Tetramer model of leukoemeraldine-emeraldine electrochemistry in the presence of trihalogenoacetic acids. DFT approach.

PubMed

Barbosa, Nuno Almeida; Grzeszczuk, Maria; Wieczorek, Robert

2015-01-15

First results of the application of the DFT computational approach to the reversible electrochemistry of polyaniline are presented. A tetrameric chain was used as the simplest model of the polyaniline polymer species. The system under theoretical investigation involved six tetramer species, two electrons, and two protons, taking part in 14 elementary reactions. Moreover, the tetramer species were interacting with two trihalogenoacetic acid molecules. Trifluoroacetic, trichloroacetic, and tribromoacetic acids were found to impact the redox transformation of polyaniline as shown by cyclic voltammetry. The theoretical approach was considered as a powerful tool for investigating the main factors of importance for the experimental behavior. The DFT method provided molecular structures, interaction energies, and equilibrium energies of all of the tetramer-acid complexes. Differences between the energies of the isolated tetramer species and their complexes with acids are discussed in terms of the elementary reactions, that is, ionization potentials and electron affinities, equilibrium constants, electrode potentials, and reorganization energies. The DFT results indicate a high impact of the acid on the reorganization energy of a particular elementary electron-transfer reaction. The ECEC oxidation path was predicted by the calculations. The model of the reacting system must be extended to octamer species and/or dimeric oligomer species to better approximate the real polymer situation.

Relevance of the DFT method to study expanded porphyrins with different topologies.

PubMed

Torrent-Sucarrat, Miquel; Navarro, Sara; Cossío, Fernando P; Anglada, Josep M; Luis, Josep M

2017-12-15

Meso-aryl expanded porphyrins present a structural versatility that allows them to achieve different topologies with distinct aromaticities. Several studies appeared in the literature studying these topological switches from an experimental and theoretical point of view. Most of these publications include density functional theory calculations, being the B3LYP the most used methodology. In this work, we show that the selection of the functional has a critical role on the geometric, energetic, and magnetic results of these expanded porphyrins, and that the use of an inadequate methodology can even generate spurious stationary points on the potential energy surface. To illustrate these aspects, in this article we have studied different molecular distortions of two expanded porphyrins, [32]-heptaphyrin and [26]-hexaphyrin using 11 DFT functionals and performing single point energy calculations at the local pair natural orbital coupled cluster DLPNO-CCSD(T) method, which have been carried out for benchmarking purposes. For some selected functionals, the dispersion effects have also been evaluated using the D3-Grimme's dispersion correction with Becke-Johnson damping. Our results let us to conclude that the CAM-B3LYP, M05-2X, and M06-2X functionals are the methodologies that provide a more consistent description of these topological switches, while other methods, such as B3LYP, BPE, and BP86, show a biased description. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

A classical density functional theory for the asymmetric restricted primitive model of ionic liquids

NASA Astrophysics Data System (ADS)

Lu, Hongduo; Nordholm, Sture; Woodward, Clifford E.; Forsman, Jan

2018-05-01

A new three-parameter (valency, ion size, and charge asymmetry) model, the asymmetric restricted primitive model (ARPM) of ionic liquids, has recently been proposed. Given that ionic liquids generally are composed of monovalent species, the ARPM effectively reduces to a two-parameter model. Monte Carlo (MC) simulations have demonstrated that the ARPM is able to reproduce key properties of room temperature ionic liquids (RTILs) in bulk and at charged surfaces. The relatively modest complexity of the model raises the possibility, which is explored here, that a classical density functional theory (DFT) could resolve its properties. This is relevant because it might generate great improvements in terms of both numerical efficiency and understanding in the continued research of RTILs and their applications. In this report, a DFT for rod-like molecules is proposed as an approximate theoretical tool for an ARPM fluid. Borrowing data on the ion pair fraction from a single bulk simulation, the ARPM is modelled as a mixture of dissociated ions and connected ion pairs. We have specifically studied an ARPM where the hard-sphere diameter is 5 Å, with the charge located 1 Å from the hard-sphere centre. We focus on fluid structure and electrochemical behaviour of this ARPM fluid, into which a model electrode is immersed. The latter is modelled as a perfect conductor, and surface polarization is handled by the method of image charges. Approximate methods, which were developed in an earlier study, to take image interactions into account, are also incorporated in the DFT. We make direct numerical comparisons between DFT predictions and corresponding simulation data. The DFT theory is implemented both in the normal mean field form with respect to the electrostatic interactions and in a correlated form based on hole formation by both steric repulsions and ion-ion Coulomb interactions. The results clearly show that ion-ion correlations play a very important role in the screening of the charged surfaces by our ARPM ionic liquid. We have studied electrostatic potentials and ion density profiles as well the differential capacitance. The mean-field DFT fails to reproduce these properties, but the inclusion of ion-ion correlation by a simple approximate treatment yields quite reasonable agreement with the corresponding simulation results. An interesting finding is that there appears to be a surface phase transition at relatively low surface charge which is readily explored by DFT, but seen also in the MC simulations at somewhat higher asymmetry.

Assessing the density functional theory-based multireference configuration interaction (DFT/MRCI) method for transition metal complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Escudero, Daniel, E-mail: escudero@kofo.mpg.de, E-mail: thiel@kofo.mpg.de; Thiel, Walter, E-mail: escudero@kofo.mpg.de, E-mail: thiel@kofo.mpg.de

2014-05-21

We report an assessment of the performance of density functional theory-based multireference configuration interaction (DFT/MRCI) calculations for a set of 3d- and 4d-transition metal (TM) complexes. The DFT/MRCI results are compared to published reference data from reliable high-level multi-configurational ab initio studies. The assessment covers the relative energies of different ground-state minima of the highly correlated CrF{sub 6} complex, the singlet and triplet electronically excited states of seven typical TM complexes (MnO{sub 4}{sup −}, Cr(CO){sub 6}, [Fe(CN){sub 6}]{sup 4−}, four larger Fe and Ru complexes), and the corresponding electronic spectra (vertical excitation energies and oscillator strengths). It includes comparisons withmore » results from different flavors of time-dependent DFT (TD-DFT) calculations using pure, hybrid, and long-range corrected functionals. The DFT/MRCI method is found to be superior to the tested TD-DFT approaches and is thus recommended for exploring the excited-state properties of TM complexes.« less

Electronic structure and electron momentum densities of Ag2CrO4

NASA Astrophysics Data System (ADS)

Meena, Seema Kumari; Ahuja, B. L.

2018-05-01

We present the first-ever experimental electron momentum density of Ag2CrO4 using 661.65 keV γ-rays from 20 Ci 137Cs source. To validate our experimental data, we have also deduced theoretical Compton profiles, energy bands and density of states using linear combination of atomic orbitals (LCAO) method in the framework of density functional theory. It is seen that the DFT-LDA gives a better agreement with experimental data than free atom model. The energy bands and density of states are also discussed.

Experimental and theoretical evaluation on the microenvironmental effect of dimethyl sulfoxide on adrenaline in acid aqueous solution

NASA Astrophysics Data System (ADS)

Yu, Zhang-Yu; Liu, Tao; Guo, Dao-Jun; Liu, Yong-Jun; Liu, Cheng-Bu

2010-12-01

The microenvironmental effect of dimethyl sulfoxide (DMSO) on adrenaline was studied by several approaches including the cyclic voltammetry (CV) of adrenaline at a platinum electrode in acid aqueous solution, the chemical shift of 1H nuclear magnetic resonance ( 1H NMR) of adrenaline, and the change of diffusion coefficient of adrenaline. The experimental results demonstrated that DMSO has significant microenvironmental effect on adrenaline, which was confirmed by the density functional theory (DFT) study on the hydrogen bond (H-bond) complexes of adrenaline with water and DMSO.

The structural, electronic and spectroscopic properties of 4FPBAPE molecule: Experimental and theoretical study

NASA Astrophysics Data System (ADS)

Tanış, Emine; Babur Sas, Emine; Kurban, Mustafa; Kurt, Mustafa

2018-02-01

The experimental and theoretical study of 4-Formyl Phenyl Boronic Acid Pinacol Ester (4FPBAPE) molecule were performed in this work. 1H, 13C NMR and UV-Vis spectra were tested in dimethyl sulfoxide (DMSO). The structural, spectroscopic properties and energies of 4FPBAPE were obtained for two potential conformers from density functional theory (DFT) with B3LYP/6-311G (d, p) and CAM-B3LYP/6-311G (d, p) basis sets. The optimal geometry of those structures was obtained according to the position of oxygen atom upon determining the scan coordinates for each conformation. The most stable conformer was found as the A2 form. The fundamental vibrations were determined based on optimized structure in terms of total energy distribution. Electronic properties such as oscillator strength, wavelength, excitation energy, HOMO, LUMO and molecular electrostatic potential and structural properties such as radial distribution functions (RDF) and probability density depending on coordination number are presented. Theoretical results of 4-FPBAPE spectra were found to be compatible with observed spectra.

Theoretical Characterizaiton of Visual Signatures

NASA Astrophysics Data System (ADS)

Kashinski, D. O.; Chase, G. M.; di Nallo, O. E.; Scales, A. N.; Vanderley, D. L.; Byrd, E. F. C.

2015-05-01

We are investigating the accuracy of theoretical models used to predict the visible, ultraviolet, and infrared spectra, as well as other properties, of product materials ejected from the muzzle of currently fielded systems. Recent advances in solid propellants has made the management of muzzle signature (flash) a principle issue in weapons development across the calibers. A priori prediction of the electromagnetic spectra of formulations will allow researchers to tailor blends that yield desired signatures and determine spectrographic detection ranges. Quantum chemistry methods at various levels of sophistication have been employed to optimize molecular geometries, compute unscaled vibrational frequencies, and determine the optical spectra of specific gas-phase species. Electronic excitations are being computed using Time Dependent Density Functional Theory (TD-DFT). A full statistical analysis and reliability assessment of computational results is currently underway. A comparison of theoretical results to experimental values found in the literature is used to assess any affects of functional choice and basis set on calculation accuracy. The status of this work will be presented at the conference. Work supported by the ARL, DoD HPCMP, and USMA.

Self-Interaction Error in Density Functional Theory: An Appraisal.

PubMed

Bao, Junwei Lucas; Gagliardi, Laura; Truhlar, Donald G

2018-05-03

Self-interaction error (SIE) is considered to be one of the major sources of error in most approximate exchange-correlation functionals for Kohn-Sham density-functional theory (KS-DFT), and it is large with all local exchange-correlation functionals and with some hybrid functionals. In this work, we consider systems conventionally considered to be dominated by SIE. For these systems, we demonstrate that by using multiconfiguration pair-density functional theory (MC-PDFT), the error of a translated local density-functional approximation is significantly reduced (by a factor of 3) when using an MCSCF density and on-top density, as compared to using KS-DFT with the parent functional; the error in MC-PDFT with local on-top functionals is even lower than the error in some popular KS-DFT hybrid functionals. Density-functional theory, either in MC-PDFT form with local on-top functionals or in KS-DFT form with some functionals having 50% or more nonlocal exchange, has smaller errors for SIE-prone systems than does CASSCF, which has no SIE.

Experimental and theoretical investigation of the first-order hyperpolarizability of a class of triarylamine derivatives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silva, Daniel L., E-mail: dlsilva.physics@gmail.com, E-mail: deboni@ifsc.usp.br; Instituto de Física, Universidade de São Paulo, CP 66318, 05314-970 São Paulo, SP; Fonseca, Ruben D.

2015-02-14

This paper reports on the static and dynamic first-order hyperpolarizabilities of a class of push-pull octupolar triarylamine derivatives dissolved in toluene. We have combined hyper-Rayleigh scattering experiment and the coupled perturbed Hartree-Fock method implemented at the Density Functional Theory (DFT) level of theory to determine the static and dynamic (at 1064 nm) first-order hyperpolarizability (β{sub HRS}) of nine triarylamine derivatives with distinct electron-withdrawing groups. In four of these derivatives, an azoaromatic unit is inserted and a pronounceable increase of the first-order hyperpolarizability is reported. Based on the theoretical results, the dipolar/octupolar character of the derivatives is determined. By using amore » polarizable continuum model in combination with the DFT calculations, it was found that although solvated in an aprotic and low dielectric constant solvent, due to solvent-induced polarization and the frequency dispersion effect, the environment substantially affects the first-order hyperpolarizability of all derivatives investigated. This statement is supported due to the solvent effects to be essential for the better agreement between theoretical results and experimental data concerning the dynamic first-order hyperpolarizability of the derivatives. The first-order hyperpolarizability of the derivatives was also modeled using the two- and three-level models, where the relationship between static and dynamic first hyperpolarizabilities is given by a frequency dispersion model. Using this approach, it was verified that the dynamic first hyperpolarizability of the derivatives is satisfactorily reproduced by the two-level model and that, in the case of the derivatives with an azoaromatic unit, the use of a damped few-level model is essential for, considering also the molecular size of such derivatives, a good quantitative agreement between theoretical results and experimental data to be observed.« less

Electronic structure investigations of 4-aminophthal hydrazide by UV-visible, NMR spectral studies and HOMO-LUMO analysis by ab initio and DFT calculations.

PubMed

Sambathkumar, K; Jeyavijayan, S; Arivazhagan, M

2015-08-05

Combined experimental and theoretical studies were conducted on the molecular structure and vibrational spectra of 4-AminoPhthalhydrazide (APH). The FT-IR and FT-Raman spectra of APH were recorded in the solid phase. The molecular geometry and vibrational frequencies of APH in the ground state have been calculated by using the ab initio HF (Hartree-Fock) and density functional methods (B3LYP) invoking 6-311+G(d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF and B3LYP method show best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of APH with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems. The difference between the observed and scaled wave number values of most of the fundamentals is very small. A detailed interpretation of the NMR spectra of APH was also reported. The theoretical spectrograms for infrared and Raman spectra of the title molecule have been constructed. UV-vis spectrum of the compound was recorded and the electronic properties, such as HOMO and LUMO energies, were performed by time dependent density functional theory (TD-DFT) approach. Finally the calculations results were applied to simulated infrared and Raman spectra of the title compound which show good agreement with observed spectra. And the temperature dependence of the thermodynamic properties of constant pressure (Cp), entropy (S) and enthalpy change (ΔH0→T) for APH were also determined. Copyright © 2015 Elsevier B.V. All rights reserved.

Multiconfigurational short-range density-functional theory for open-shell systems

NASA Astrophysics Data System (ADS)

Hedegârd, Erik Donovan; Toulouse, Julien; Jensen, Hans Jørgen Aagaard

2018-06-01

Many chemical systems cannot be described by quantum chemistry methods based on a single-reference wave function. Accurate predictions of energetic and spectroscopic properties require a delicate balance between describing the most important configurations (static correlation) and obtaining dynamical correlation efficiently. The former is most naturally done through a multiconfigurational (MC) wave function, whereas the latter can be done by, e.g., perturbation theory. We have employed a different strategy, namely, a hybrid between multiconfigurational wave functions and density-functional theory (DFT) based on range separation. The method is denoted by MC short-range DFT (MC-srDFT) and is more efficient than perturbative approaches as it capitalizes on the efficient treatment of the (short-range) dynamical correlation by DFT approximations. In turn, the method also improves DFT with standard approximations through the ability of multiconfigurational wave functions to recover large parts of the static correlation. Until now, our implementation was restricted to closed-shell systems, and to lift this restriction, we present here the generalization of MC-srDFT to open-shell cases. The additional terms required to treat open-shell systems are derived and implemented in the DALTON program. This new method for open-shell systems is illustrated on dioxygen and [Fe(H2O)6]3+.

Application of Density Functional Theory to Systems Containing Metal Atoms

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.

2006-01-01

The accuracy of density functional theory (DFT) for problems involving metal atoms is considered. The DFT results are compared with experiment as well as results obtained using the coupled cluster approach. The comparisons include geometries, frequencies, and bond energies. The systems considered include MO2, M(OH)+n, MNO+, and MCO+2. The DFT works well for frequencies and geometries, even in case with symmetry breaking; however, some examples have been found where the symmetry breaking is quite severe and the DFT methods do not work well. The calculation of bond energies is more difficult and examples of successes as well as failures of DFT will be given.

The standard mean-field treatment of inter-particle attraction in classical DFT is better than one might expect

NASA Astrophysics Data System (ADS)

Archer, Andrew J.; Chacko, Blesson; Evans, Robert

2017-07-01

In classical density functional theory (DFT), the part of the Helmholtz free energy functional arising from attractive inter-particle interactions is often treated in a mean-field or van der Waals approximation. On the face of it, this is a somewhat crude treatment as the resulting functional generates the simple random phase approximation (RPA) for the bulk fluid pair direct correlation function. We explain why using standard mean-field DFT to describe inhomogeneous fluid structure and thermodynamics is more accurate than one might expect based on this observation. By considering the pair correlation function g(x) and structure factor S(k) of a one-dimensional model fluid, for which exact results are available, we show that the mean-field DFT, employed within the test-particle procedure, yields results much superior to those from the RPA closure of the bulk Ornstein-Zernike equation. We argue that one should not judge the quality of a DFT based solely on the approximation it generates for the bulk pair direct correlation function.

Benchmarking Density Functional Theory Based Methods To Model NiOOH Material Properties: Hubbard and van der Waals Corrections vs Hybrid Functionals.

PubMed

Zaffran, Jeremie; Caspary Toroker, Maytal

2016-08-09

NiOOH has recently been used to catalyze water oxidation by way of electrochemical water splitting. Few experimental data are available to rationalize the successful catalytic capability of NiOOH. Thus, theory has a distinctive role for studying its properties. However, the unique layered structure of NiOOH is associated with the presence of essential dispersion forces within the lattice. Hence, the choice of an appropriate exchange-correlation functional within Density Functional Theory (DFT) is not straightforward. In this work, we will show that standard DFT is sufficient to evaluate the geometry, but DFT+U and hybrid functionals are required to calculate the oxidation states. Notably, the benefit of DFT with van der Waals correction is marginal. Furthermore, only hybrid functionals succeed in opening a bandgap, and such methods are necessary to study NiOOH electronic structure. In this work, we expect to give guidelines to theoreticians dealing with this material and to present a rational approach in the choice of the DFT method of calculation.

Benchmark CCSD(T) and DFT study of binding energies in Be7 - 12: in search of reliable DFT functional for beryllium clusters

NASA Astrophysics Data System (ADS)

Labanc, Daniel; Šulka, Martin; Pitoňák, Michal; Černušák, Ivan; Urban, Miroslav; Neogrády, Pavel

2018-05-01

We present a computational study of the stability of small homonuclear beryllium clusters Be7 - 12 in singlet electronic states. Our predictions are based on highly correlated CCSD(T) coupled cluster calculations. Basis set convergence towards the complete basis set limit as well as the role of the 1s core electron correlation are carefully examined. Our CCSD(T) data for binding energies of Be7 - 12 clusters serve as a benchmark for performance assessment of several density functional theory (DFT) methods frequently used in beryllium cluster chemistry. We observe that, from Be10 clusters on, the deviation from CCSD(T) benchmarks is stable with respect to size, and fluctuating within 0.02 eV error bar for most examined functionals. This opens up the possibility of scaling the DFT binding energies for large Be clusters using CCSD(T) benchmark values for smaller clusters. We also tried to find analogies between the performance of DFT functionals for Be clusters and for the valence-isoelectronic Mg clusters investigated recently in Truhlar's group. We conclude that it is difficult to find DFT functionals that perform reasonably well for both beryllium and magnesium clusters. Out of 12 functionals examined, only the M06-2X functional gives reasonably accurate and balanced binding energies for both Be and Mg clusters.

Uniform magnetic fields in density-functional theory

NASA Astrophysics Data System (ADS)

Tellgren, Erik I.; Laestadius, Andre; Helgaker, Trygve; Kvaal, Simen; Teale, Andrew M.

2018-01-01

We construct a density-functional formalism adapted to uniform external magnetic fields that is intermediate between conventional density functional theory and Current-Density Functional Theory (CDFT). In the intermediate theory, which we term linear vector potential-DFT (LDFT), the basic variables are the density, the canonical momentum, and the paramagnetic contribution to the magnetic moment. Both a constrained-search formulation and a convex formulation in terms of Legendre-Fenchel transformations are constructed. Many theoretical issues in CDFT find simplified analogs in LDFT. We prove results concerning N-representability, Hohenberg-Kohn-like mappings, existence of minimizers in the constrained-search expression, and a restricted analog to gauge invariance. The issue of additivity of the energy over non-interacting subsystems, which is qualitatively different in LDFT and CDFT, is also discussed.

Experimental and theoretical investigations of functionalized boron nitride as electrode materials for Li-ion batteries

DOE PAGES

Zhang, Fan; Nemeth, Karoly; Bareno, Javier; ...

2016-03-03

The feasibility of synthesizing functionalized h-BN (FBN) via the reaction between molten LiOH and solid h-BN is studied for the first time and its first ever application as an electrode material in Li-ion batteries is evaluated. Density functional theory (DFT) calculations are performed to provide mechanistic understanding of the possible electrochemical reactions derived from the FBN. Various materials characterizations reveal that the melt-solid reaction can lead to exfoliation and functionalization of h-BN simultaneously, while electrochemical analysis proves that the FBN can reversibly store charges through surface redox reactions with good cycle stability and coulombic efficiency. As a result, the DFTmore » calculations have provided physical insights into the observed electrochemical properties derived from the FBN.« less

Uniform magnetic fields in density-functional theory.

PubMed

Tellgren, Erik I; Laestadius, Andre; Helgaker, Trygve; Kvaal, Simen; Teale, Andrew M

2018-01-14

We construct a density-functional formalism adapted to uniform external magnetic fields that is intermediate between conventional density functional theory and Current-Density Functional Theory (CDFT). In the intermediate theory, which we term linear vector potential-DFT (LDFT), the basic variables are the density, the canonical momentum, and the paramagnetic contribution to the magnetic moment. Both a constrained-search formulation and a convex formulation in terms of Legendre-Fenchel transformations are constructed. Many theoretical issues in CDFT find simplified analogs in LDFT. We prove results concerning N-representability, Hohenberg-Kohn-like mappings, existence of minimizers in the constrained-search expression, and a restricted analog to gauge invariance. The issue of additivity of the energy over non-interacting subsystems, which is qualitatively different in LDFT and CDFT, is also discussed.

Structural, theoretical and corrosion inhibition studies on some transition metal complexes derived from heterocyclic system

NASA Astrophysics Data System (ADS)

Gupta, Shraddha Rani; Mourya, Punita; Singh, M. M.; Singh, Vinod P.

2017-06-01

A Schiff base, (E)-N‧-((1H-indol-3-yl)methylene)-2-aminobenzohydrazide (Iabh) and its Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes have been synthesized. These compounds have been characterized by different physico-chemical and spectroscopic tools (UV-Vis, IR, NMR and ESI-Mass). The molecular structure of Iabh is determined by single crystal X-ray diffraction technique. The ligand Iabh displays E-configuration about the >Cdbnd N- bond. The structure of ligand is stabilized by intra-molecular H-bonding. In all the metal complexes the ligand coordinates through azomethine-N and carbonyl-O resulting a distorted octahedral geometry for Mn(II), Co(II) and Cu(II) complexes in which chloride ions occupy axial positions. Ni(II) and Zn(II) complexes, however, form 4-coordinate distorted square planer and tetrahedral geometry around metal ion, respectively. The structures of the complexes have been satisfactorily modeled by calculations based on density functional theory (DFT) and time dependent-DFT (TD-DFT). The corrosion inhibition study of the compounds have been performed against mild steel in 0.5 M H2SO4 solution at 298 K by using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). They show appreciable corrosion inhibition property.

Symmetry and structure of carbon-nitrogen complexes in gallium arsenide from infrared spectroscopy and first-principles calculations

NASA Astrophysics Data System (ADS)

Künneth, Christopher; Kölbl, Simon; Wagner, Hans Edwin; Häublein, Volker; Kersch, Alfred; Alt, Hans Christian

2018-04-01

Molecular-like carbon-nitrogen complexes in GaAs are investigated both experimentally and theoretically. Two characteristic high-frequency stretching modes at 1973 and 2060 cm-1, detected by Fourier transform infrared absorption (FTIR) spectroscopy, appear in carbon- and nitrogen-implanted and annealed layers. From isotopic substitution, it is deduced that the chemical composition of the underlying complexes is CN2 and C2N, respectively. Piezospectroscopic FTIR measurements reveal that both centers have tetragonal symmetry. For density functional theory (DFT) calculations, linear entities are substituted for the As anion, with the axis oriented along the 〈1 0 0 〉 direction, in accordance with the experimentally ascertained symmetry. The DFT calculations support the stability of linear N-C-N and C-C-N complexes in the GaAs host crystal in the charge states ranging from + 3 to -3. The valence bonds of the complexes are analyzed using molecular-like orbitals from DFT. It turns out that internal bonds and bonds to the lattice are essentially independent of the charge state. The calculated vibrational mode frequencies are close to the experimental values and reproduce precisely the isotopic mass splitting from FTIR experiments. Finally, the formation energies show that under thermodynamic equilibrium CN2 is more stable than C2N.

Linoleic acid and its potassium and sodium salts: A combined experimental and theoretical study

NASA Astrophysics Data System (ADS)

Gocen, Tuğba; Haman Bayarı, Sevgi; Haluk Guven, Mehmet

2017-12-01

Linoleic acid (cis, cis-9,12-octodecadienoic acid) is the main polyunsaturated -omega 6- essential fatty acid. The conformational behaviour of linoleic acid (LA) in the gas phase was investigated by means of density functional theory (DFT). The structures of conformers of LA were fully optimized by using the B3LYP/6-311++G(d,p) method. The theory showed that the tttttts‧CssCs‧tt conformation of LA (conformer I) is the more stable than the other conformations. Fourier Transform Infrared (FTIR) and micro-Raman spectra of pure LA in liquid form were recorded in the region 4000-450 and 3500-100 cm-1, respectively. The DFT calculations on the molecular structure and vibrational spectra of the dimer form of most stable conformer of LA were also performed using the same method. The assignment of the vibrational modes was made based on calculated potential energy distributions (PEDs). The simulated spectra of dimer form of LA are in reasonably good agreement with the experimental spectra. The sodium and potassium salts of LA were synthesized and characterized by FTIR and Raman spectroscopy, X-ray diffraction and DFT calculations. Several molecular and electronic properties of LA and its salts such as HOMO-LUMO energies, chemical hardness and electronegativity were also calculated and interpreted.

Rationalization of Hubbard U in CeOx from first principles: Unveiling the role of local structure in screening

NASA Astrophysics Data System (ADS)

Lu, Deyu; Liu, Ping

2014-03-01

DFT+U method has been widely employed in theoretical studies on various ceria systems to correct the delocalization bias in local and semi-local DFT functionals with moderate computational cost. To rationalize the Hubbard U of Ce 4f, we employed the first principles linear response method to compute Hubbard U for Ce in ceria clusters, bulks, and surfaces. We found that in contrast to the commonly used approach treating U as a constant, the Hubbard U varies in a wide range from 4.1 eV to 6.7 eV, and exhibits a strong correlation with the Ce coordination numbers and Ce-O bond lengths, rather than the Ce 4f valence state. The variation of the Hubbard U can be explained by the changes in the strength of local screening due to O --> Ce intersite transition. Our study represents a systematic, quantitative investigation of the relationship between the Hubbard U and the local atomic arrangement, enabling a DFT+environment-dependent U scheme that can have potential impact on catalysis research of strongly correlated systems. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

Investigation of antimicrobial activities, DNA interaction, structural and spectroscopic properties of 2-chloro-6-(trifluoromethyl)pyridine

NASA Astrophysics Data System (ADS)

Evecen, Meryem; Kara, Mehmet; Idil, Onder; Tanak, Hasan

2017-06-01

2-Chloro-6-(trifluoromethyl)pyridine has been characterized by FT-IR, 1H and 13C NMR experiment. FT-IR spectra of the molecule has been recorded in the 4000-400 cm-1 region. The molecular structural parameters and vibrational frequencies were computed using the HF and DFT (B3LYP, B3PW91) methods with the 6-31+G(d,p) and 6-311++G(d,p) basis sets. 1H and 13C NMR Gauge Including Atomic Orbital (GIAO) chemical shifts of the compound were calculated using the density functional method (B3LYP) with the 6-311++G(d,p) basis set. The vibrational wavenumbers and chemical shifts were compared with the experimental data of the compound. Using the TD-DFT methodology, electronic absorption spectra of the compound have been computed. Besides, solvent effects on the excitation energies and chemical shifts were carried out using the integral equation formalism of the polarisable continuum model (IEF-PCM). DFT calculations of the compound, Mulliken's charges, molecular electrostatic potential (MEP), natural bond orbital (NBO) and thermodynamic properties were also obtained theoretically. In addition, the antimicrobial activities were tested by using minimal inhibitory concentration method (MIC) and also the effect of the molecule on pBR322 plasmid DNA was monitored byagarose gel electrophoresis experiments.

Potential energy distribution (PED) analysis of DFT calculated IR spectra of the most stable Li, Na, and Cu(I) diformate molecules

NASA Astrophysics Data System (ADS)

Jamróz, M. H.; Dobrowolski, J. Cz.

2001-05-01

For the most stable Li, Na, and Cu(I) diformates we present the vibrational spectra, supported by potential energy distribution (PED) analysis, and the interaction energies between formic acid and metal formate by the DFT (B3PW91) method. PED analysis of the theoretical spectra forms the basis for the elucidation of the future matrix isolation IR spectra.

On the Reliability of Pure and Hybrid DFT Methods for the Evaluation of Halogen, Chalcogen, and Pnicogen Bonds Involving Anionic and Neutral Electron Donors.

PubMed

Bauzá, Antonio; Alkorta, Ibon; Frontera, Antonio; Elguero, José

2013-11-12

In this article, we report a comprehensive theoretical study of halogen, chalcogen, and pnicogen bonding interactions using a large set of pure and hybrid functionals and some ab initio methods. We have observed that the pure and some hybrid functionals largely overestimate the interaction energies when the donor atom is anionic (Cl(-) or Br(-)), especially in the halogen bonding complexes. To evaluate the reliability of the different DFT (BP86, BP86-D3, BLYP, BLYP-D3, B3LYP, B97-D, B97-D3, PBE0, HSE06, APFD, and M06-2X) and ab initio (MP2, RI-MP2, and HF) methods, we have compared the binding energies and equilibrium distances to those obtained using the CCSD(T)/aug-cc-pVTZ level of theory, as reference. The addition of the latest available correction for dispersion (D3) to pure functionals is not recommended for the calculation of halogen, chalcogen, and pnicogen complexes with anions, since it further contributes to the overestimation of the binding energies. In addition, in chalcogen bonding interactions, we have studied how the hybridization of the chalcogen atom influences the interaction energies.

Functionalization of SBA-15 mesoporous silica by Cu-phosphonate units: Probing of synthesis route

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laskowski, Lukasz, E-mail: lukasz.laskowski@kik.pcz.pl; Czestochowa University of Technology, Institute of Physics, Al. Armii Krajowej 19, 42-201 Czestochowa; Laskowska, Magdalena, E-mail: magdalena.laskowska@onet.pl

2014-12-15

Mesoporous silica SBA-15 containing propyl-copper phosphonate units was investigated. The structure of mesoporous samples was tested by N{sub 2} isothermal sorption (BET and BHJ analysis), TEM microscopy and X-Ray scattering. Quantitative analysis EDX has given information about proportions between component atoms in the sample. Quantitative elemental analysis has been carried out to support EDX. To examine bounding between copper atoms and phosphonic units the Raman spectroscopy was carried out. As a support of Raman scattering, the theoretical calculations were made based on density functional theory, with the B3LYP method. By comparison of the calculated vibrational spectra of the molecule withmore » experimental results, distribution of the active units inside silica matrix has been determined. - Graphical abstract: The present study is devoted to mesoporous silica SBA-15 containing propyl-copper phosphonate units. The species were investigated to confirm of synthesis procedure correctness by the micro-Raman technique combined with DFT numerical simulations. Complementary research was carried out to test the structure of mesoporous samples. - Highlights: • SBA-15 silica functionalized with propyl-copper phosphonate units was synthesized. • Synthesis efficiency probed by Raman study supported with DFT simulations. • Homogenous distribution of active units was proved. • Synthesis route enables precise control of distance between copper ions.« less

Theoretical Modeling of (99)Tc NMR Chemical Shifts.

PubMed

Hall, Gabriel B; Andersen, Amity; Washton, Nancy M; Chatterjee, Sayandev; Levitskaia, Tatiana G

2016-09-06

Technetium-99 (Tc) displays a rich chemistry due to its wide range of accessible oxidation states (from -I to +VII) and ability to form coordination compounds. Determination of Tc speciation in complex mixtures is a major challenge, and (99)Tc nuclear magnetic resonance (NMR) spectroscopy is widely used to probe chemical environments of Tc in odd oxidation states. However, interpretation of (99)Tc NMR data is hindered by the lack of reference compounds. Density functional theory (DFT) calculations can help to fill this gap, but to date few computational studies have focused on (99)Tc NMR of compounds and complexes. This work evaluates the effectiveness of both pure generalized gradient approximation and their corresponding hybrid functionals, both with and without the inclusion of scalar relativistic effects, to model the (99)Tc NMR spectra of Tc(I) carbonyl compounds. With the exception of BLYP, which performed exceptionally well overall, hybrid functionals with inclusion of scalar relativistic effects are found to be necessary to accurately calculate (99)Tc NMR spectra. The computational method developed was used to tentatively assign an experimentally observed (99)Tc NMR peak at -1204 ppm to fac-Tc(CO)3(OH)3(2-). This study examines the effectiveness of DFT computations for interpretation of the (99)Tc NMR spectra of Tc(I) coordination compounds in high salt alkaline solutions.

Accurate simulation of geometry, singlet-singlet and triplet-singlet excitation of cyclometalated iridium(III) complex.

PubMed

Wang, Jian; Bai, Fu-Quan; Xia, Bao-Hui; Zhang, Hong-Xing; Cui, Tian

2014-03-01

In the current contribution, we present a critical study of the theoretical protocol used for the determination of the electronic spectra properties of luminescent cyclometalated iridium(III) complex, [Ir(III)(ppy)₂H₂dcbpy]⁺ (where, ppy = 2-phenylpyridine, H₂dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid), considered as a representative example of the various problems related to the prediction of electronic spectra of transition metal complex. The choice of the exchange-correlation functional is crucial for the validity of the conclusions that would be drawn from the numerical results. The influence of the exchange-correlation on geometry parameter and absorption/emission band, the role of solvent effects on time-dependent density function theory (TD-DFT) calculations, as well as the importance of the chosen proper procedure to optimize triplet excited geometry, have been thus examined in detail. From the obtained results, some general conclusions and guidelines are presented: i) PBE0 functional is the most accurate in prediction of ground state geometry; ii) the well-established B3LYP, B3P86, PBE0, and X3LYP have similar accuracy in calculation of absorption spectrum; and iii) the hybrid approach TD-DFT//CIS gives out excellent agreement in the evaluation of triplet excitation energy.

Density functional theory for open-shell singlet biradicals

NASA Astrophysics Data System (ADS)

Gräfenstein, Jürgen; Kraka, Elfi; Cremer, Dieter

1998-05-01

The description of open-shell singlet (OSS) σ- π biradicals by density functional theory (DFT) requires at least a two-configurational (TC) or, in general, a MC-DFT approach, which bears many unsolved problems. These can be avoided by reformulating the TC description in the spirit of restricted open shell theory for singlets (ROSS) and developing an exchange-correlation functional for ROSS-DFT. ROSS-DFT turns out to lead to reliable descriptions of geometry and vibrational frequencies for OSS biradicals. The relative energies of the OSS states obtained at the ROSS-B3LYP/6-311G(d,p) level are often better than the corresponding ROSS-MP2 results. However, in those cases where spin polarization in a conjugated π systems plays a role, DFT predicts the triplet state related to the OSS state 2-4 kcal/mol too stable.

Antimycobacterial, antimicrobial activity, experimental (FT-IR, FT-Raman, NMR, UV-Vis, DSC) and DFT (transition state, chemical reactivity, NBO, NLO) studies on pyrrole-isonicotinyl hydrazine

NASA Astrophysics Data System (ADS)

Rawat, Poonam; Singh, R. N.; Ranjan, Alok; Ahmad, Sartaj; Saxena, Rajat

2017-05-01

As part of a study of pyrrole hydrazone, we have investigated quantum chemical calculations, molecular geometry, relative energy, vibrational properties and antimycobacterial/antimicrobial activity of pyrrole-2-carboxaldehyde isonicotinyl hydrazone (PCINH), by applying the density functional theory (DFT) and Hartree Fock (HF). Good reproduction of experimental values is obtained and with small percentage error in majority of the cases in comparison to theoretical result (DFT). The experimental FT-IR and Raman wavenumbers were compared with the respective theoretical values obtained from DFT calculations and found to agree well. In crystal structure studies the hydrated PCINH (syn-syn conformer) shows different conformation than from anhydrous form (syn-anti conformer). The rotational barrier between syn-syn and syn-anti conformers of PCINH is 12.7 kcal/mol in the gas phase. In this work, use of FT-IR, FT-Raman, 1H NMR, 13C NMR and UV-Vis spectroscopies has been made for full characterization of PCINH. A detailed interpretation of the vibrational spectrum was carried out with the aid of normal coordinate analysis using single scaling factor. Our results support the hydrogen bonding pattern proposed by reported crystalline structure. The calculated nature of electronic transitions within molecule found to be π → π*. The electronic descriptors study indicates that PCINH can be used as robust synthon for synthesis of new heterocyclic compounds. The first static hyperpolarizability (β0) of PCINH is calculated as 33.89 × 10- 30 esu, (gas phase); 68.79 × 10- 30 (CHCl3), esu; 76.76 × 10- 30 esu (CH2Cl2), 85.16 × 10- 30 esu (DMSO). The solvent induced effects on the first static hyperpolarizability were studied and found to increase as dielectric constants of the solvents increases. Investigated molecule shows better NLO value than Para nitroaniline (PNA). The compound PCINH shows good antifungal and antibacterial activity against Aspergillus niger and gram-positive bacteria Bacillus subtilis, respectively. The compound also shows good antituberculosis activity against Mycobacterium tuberculosis H37Rv using the microplate alamar blue assay (MABA).

Quantum chemical protocols for modeling reactions and spectra in astrophysical ice analogs: the challenging case of the C⁺ + H₂O reaction in icy grain mantles.

PubMed

Woon, David E

2015-11-21

Icy grain mantles that accrete on refractory dust particles in the very cold interstellar medium or beyond the snow line in protoplanetary disks serve as minute incubators for heterogeneous chemistry. Ice mantle chemistry can differ significantly from the gas phase chemistry that occurs in these environments and is often richer. Modeling ices and their chemistry is a challenging task for quantum theoretical methods, but theory promises insight into these systems that is difficult to attain with experiments. Density functional theory (DFT) is predominately employed for modeling reactions in icy grain mantles due to its favorable scalability, but DFT has limitations that risk undercutting its reliability for this task. In this work, basic protocols are proposed for identifying the degree to which DFT methods are able to reproduce experimental or higher level theoretical results for the fundamental interactions upon which ice mantle chemistry depends, including both reactive interactions and non-reactive scaffolding interactions. The exemplar of this study is the reaction of C(+) with H2O, where substantial methodological differences are found in the prediction of gas phase relative energetics for stationary points (about 10 kcal mol(-1) for the C-O bond energy of the H2OC(+) intermediate), which in turn casts doubt about employing it to treat the C(+) + H2O reaction on an ice surface. However, careful explorations demonstrate that B3LYP with small correlation consistent basis sets performs in a sufficiently reliable manner to justify using it to identify plausible chemical pathways, where the dominant products were found to be neutral HOC and the CO(-) anion plus one and two H3O(+) cations, respectively. Predicted vibrational and electronic spectra are presented that would serve to verify or disconfirm the pathways; the latter were computed with time-dependent DFT. Conclusions are compared with those of a recent similar study by McBride and coworkers (J. Phys. Chem. A, 2014, 118, 6991).

Optical properties of LiGaS2: an ab initio study and spectroscopic ellipsometry measurement

NASA Astrophysics Data System (ADS)

Atuchin, V. V.; Lin, Z. S.; Isaenko, L. I.; Kesler, V. G.; Kruchinin, V. N.; Lobanov, S. I.

2009-11-01

Electronic and optical properties of lithium thiogallate crystal, LiGaS2, have been investigated by both experimental and theoretical methods. The plane-wave pseudopotential method based on DFT theory has been used for band structure calculations. The electronic parameters of Ga 3d orbitals have been corrected by the DFT+U methods to be consistent with those measured with x-ray photoemission spectroscopy. Evolution of optical constants of LiGaS2 over a wide spectral range was determined by developed first-principles theory and dispersion curves were compared with optical parameters defined by spectroscopic ellipsometry in the photon energy range 1.2-5.0 eV. Good agreement has been achieved between theoretical and experimental results.

Benchmark results and theoretical treatments for valence-to-core x-ray emission spectroscopy in transition metal compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mortensen, D. R.; Seidler, G. T.; Kas, Joshua J.

We report measurement of the valence-to-core (VTC) region of the K-shell x-ray emission spectra from several Zn and Fe inorganic compounds, and their critical comparison with several existing theoretical treatments. We find generally good agreement between the respective theories and experiment, and in particular find an important admixture of dipole and quadrupole character for Zn materials that is much weaker in Fe-based systems. These results on materials whose simple crystal structures should not, a prior, pose deep challenges to theory, will prove useful in guiding the further development of DFT and time-dependent DFT methods for VTC-XES predictions and their comparisonmore » to experiment.« less

Binaphthyl-containing Schiff base complexes with carboxyl groups for dye sensitized solar cell: An experimental and theoretical study

NASA Astrophysics Data System (ADS)

Tsaturyan, Arshak; Machida, Yosuke; Akitsu, Takashiro; Gozhikova, Inna; Shcherbakov, Igor

2018-06-01

We report on synthesis and characterization of binaphthyl containing Schiff base Ni(II), Cu(II), and Zn(II) complexes as promising photosensitizers for dye-sensitized solar cells (DSSC). Based on theoretical and experimental data, the possibility of their application in DSSC was confirmed. To our knowledge, we find dye performance of complex is steric and rigid structure widely spread to efficiency. The spatial and electronic structures of the complexes were studied by means of the quantum chemical modeling using DFT and TD-DFT approaches. The adsorption energies of the complexes on TiO2 cluster were calculated and appeared to be very close in value. The Zn(II) complex has the biggest value of molar extinction.

A theoretical study on 3-(4-methoxyphenyl)-1-(pyridin-2-Yl) prop-2-en-1-one

DOE Office of Scientific and Technical Information (OSTI.GOV)

Öner, Nazmiye, E-mail: fizikcinaz@gmail.com; Tamer, Ömer, E-mail: omertamer@sakarya.edu.tr; Avci, Davut, E-mail: davcir@sakarya.edu.tr

This study reports the geometric parameters, vibration frequencies, {sup 13}C and {sup 1}H NMR chemical shifts of 3-(4-Methoxyphenyl)-1-(pyridin-2-yl) prop-2-en-1-one (MPP) molecule calculated by B3LYP level of density functional theory (DFT) with 6-311++G(d,p) basis set. {sup 13}C and {sup 1}H NMR chemical shifts were calculated within GIAO approach which is one of the most common approaches. Additionally, 3D molecular surfaces such as molecular electrostatic potential (MEP) and electrostatic potential (ESP), were simulated by the same level. As a result, obtained theoretical results were found to be consistent with experimental ones. All of calculations were carried out Gaussian 09 package program.

Conformational, spectroscopic and nonlinear optical properties of biologically active N,N-dimethyltryptamine molecule: a theoretical study.

PubMed

Öner, Nazmiye; Tamer, Ömer; Avcı, Davut; Atalay, Yusuf

2014-12-10

The effective psychoactive properties of N,N-dimethyltryptamine (DMT) known as the near-death molecule have encouraged the imagination of many research disciplines for several decades. Although there is no theoretical study, a number of paper composed by experimental techniques have been reported for DMT molecule. In this study, the molecular modeling of DMT was carried out using B3LYP and HSEh1PBE levels of density functional theory (DFT). Our calculations showed that the energy gap between HOMO and LUMO is low, demonstrating that DMT is a biologically active molecule. Large hyperconjugation interaction energies imply that molecular charge transfer occurs in DMT. Moreover, NLO analysis indicates that DMT can be used an effective NLO material. Copyright © 2014 Elsevier B.V. All rights reserved.

SERS and DFT study of copper surfaces coated with corrosion inhibitor

PubMed Central

Muniz-Miranda, Francesco; Caporali, Stefano

2014-01-01

Summary Azole derivatives are common inhibitors of copper corrosion due to the chemical adsorption occurring on the metal surface that gives rise to a protective film. In particular, 1,2,4-triazole performs comparable to benzotriazole, which is much more widely used, but is by no means an environmentally friendly agent. In this study, we have analyzed the adsorption of 1,2,4-triazole on copper by taking advantage of the surface-enhanced Raman scattering (SERS) effect, which highlights the vibrational features of organic ligand monolayers adhering to rough surfaces of some metals such as gold, silver and copper. To ensure the necessary SERS activation, a roughening procedure was implemented on the copper substrates, resulting in nanoscale surface structures, as evidenced by microscopic investigation. To obtain sufficient information on the molecule–metal interaction and the formation of an anticorrosive thin film, the SERS spectra were interpreted with the aid of theoretical calculations based on the density functional theory (DFT) approach. PMID:25671144

Solubility prediction of naphthalene in carbon dioxide from crystal microstructure

NASA Astrophysics Data System (ADS)

Sang, Jiarong; Jin, Junsu; Mi, Jianguo

2018-03-01

Crystals dissolved in solvents are ubiquitous in both natural and artificial systems. Due to the complicated structures and asymmetric interactions between the crystal and solvent, it is difficult to interpret the dissolution mechanism and predict solubility using traditional theories and models. Here we use the classical density functional theory (DFT) to describe the crystal dissolution behavior. As an example, naphthalene dissolved in carbon dioxide (CO2) is considered within the DFT framework. The unit cell dimensions and microstructure of crystalline naphthalene are determined by minimizing the free-energy of the crystal. According to the microstructure, the solubilities of naphthalene in CO2 are predicted based on the equality of naphthalene's chemical potential in crystal and solution phases, and the interfacial structures and free-energies between different crystal planes and solution are determined to investigate the dissolution mechanism at the molecular level. The theoretical predictions are in general agreement with the available experimental data, implying that the present model is quantitatively reliable in describing crystal dissolution.

The electronic characterization of biphenylene—Experimental and theoretical insights from core and valence level spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lüder, Johann; Sanyal, Biplab; Eriksson, Olle

In this paper, we provide detailed insights into the electronic structure of the gas phase biphenylene molecule through core and valence spectroscopy. By comparing results of X-ray Photoelectron Spectroscopy (XPS) measurements with ΔSCF core-hole calculations in the framework of Density Functional Theory (DFT), we could decompose the characteristic contributions to the total spectra and assign them to non-equivalent carbon atoms. As a difference with similar molecules like biphenyl and naphthalene, an influence of the localized orbitals on the relative XPS shifts was found. The valence spectrum probed by photoelectron spectroscopy at a photon energy of 50 eV in conjunction withmore » hybrid DFT calculations revealed the effects of the localization on the electronic states. Using the transition potential approach to simulate the X-ray absorption spectroscopy measurements, similar contributions from the non-equivalent carbon atoms were determined from the total spectrum, for which the slightly shifted individual components can explain the observed asymmetric features.« less

Understanding the Interface Dipole of Copper Phthalocyanine (CuPc)/C60: Theory and Experiment.

PubMed

Sai, Na; Gearba, Raluca; Dolocan, Andrei; Tritsch, John R; Chan, Wai-Lun; Chelikowsky, James R; Leung, Kevin; Zhu, Xiaoyang

2012-08-16

Interface dipole determines the electronic energy alignment in donor/acceptor interfaces and plays an important role in organic photovoltaics. Here we present a study combining first principles density functional theory (DFT) with ultraviolet photoemission spectroscopy (UPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate the interface dipole, energy level alignment, and structural properties at the interface between CuPc and C60. DFT finds a sizable interface dipole for the face-on orientation, in quantitative agreement with the UPS measurement, and rules out charge transfer as the origin of the interface dipole. Using TOF-SIMS, we show that the interfacial morphology for the bilayer CuPc/C60 film is characterized by molecular intermixing, containing both the face-on and the edge-on orientation. The complementary experimental and theoretical results provide both insight into the origin of the interface dipole and direct evidence for the effect of interfacial morphology on the interface dipole.

Structural and vibrational properties of oxcarbazepine, an anticonvulsant substance by using DFT and SCRF calculations

NASA Astrophysics Data System (ADS)

Ladetto, María F.; Márquez, María B.; Brandán, Silvia A.

2014-10-01

In this work, we have presented a structural and vibrational study on the properties in gas and aqueous solution phases of oxcarbazepine, a polymorphic anticonvulsant substance, combining the available IR and Raman spectra with Density Functional Theory (DFT) calculations. Two stable C1 and C2 forms for the title molecule were theoretically determined by using the hybrid B3LYP/6-31G* method. The integral equation formalism variant polarised continuum model (IEFPCM) was employed to study the solvent effects by means of the self-consistent reaction field (SCRF) method. The vibrational spectra for the two forms of oxcarbazepine were completely assigned together with two dimeric species also observed in the solid phase. The presences of the two C1 and C2 forms together with the two dimeric species are supported by the IR and Raman bands between 1424 and 125 cm-1. Here, the properties for both forms of oxcarbazepine are compared and discussed.

Ca K-Edge XAS as a Probe of Calcium Centers in Complex Systems

DOE PAGES

Martin-Diaconescu, Vlad; Gennari, Marcello; Gerey, Bertrand; ...

2014-12-10

Calcium K-edge pre-edges coupled with TD-DFT theoretical calculation of spectra provide a powerful approach for the characterization of complex calcium centers in inorganic and bioinorganic chemistry. Herein, Ca K-edge X-ray absorption spectroscopy (XAS) is developed as a means to characterize the local environment of calcium centers. The spectra for six, seven, and eight coordinate inorganic and molecular calcium complexes were analyzed and determined to be primarily influenced by the coordination environment and site symmetry at the calcium center. The experimental results are closely correlated to time-dependent density functional theory (TD-DFT) calculations of the XAS spectra. The applicability of this methodologymore » to complex systems was investigated using structural mimics of the oxygen-evolving complex (OEC) of PSII. It was found that Ca K-edge XAS is a sensitive probe for structural changes occurring in the cubane heterometallic cluster due to Mn oxidation. Future applications to the OEC are discussed.« less

A study on the electronic spectra of some 2-azidobenzothiazoles, TD-DFT treatment.

PubMed

Abu-Eittah, Rafie H; El-Taher, Sabry; Hassan, Walid; Noamaan, Mahmoud

2015-12-05

The electronic absorption spectra of some 2-azidobenzothiazoles were measured in different solvents. The effects of solvent and substitution on the spectra were investigated. Substitution by a bromine atom and by a nitro group have significant effects on both band maxima and band intensity. Correlation between the spectra of the studied compounds and the corresponding hydrocarbons proved to be weak, whereas the correlation between the observed spectra and those calculated is adequate. Theoretical treatment of the ultraviolet spectra of the studied compounds was carried out by using the TD-DFT procedures, at the B3LYP level and the 6-311+G(∗∗) basis sets, the results compared well with the experimental values. The computed molecular orbitals of the ground state indicate that some orbitals are "localized-π" or "localized σ" molecular orbitals while the others are delocalized orbitals. The calculated functions of the excited states lead to an accurate assignment of the bands observed in the spectra. Copyright © 2015. Published by Elsevier B.V.

FT-IR spectroscopy combined with DFT calculation to explore solvent effects of vinyl acetate

NASA Astrophysics Data System (ADS)

Chen, Yi; Zhang, Hui; Liu, Qing

The infrared vibration frequencies of vinyl acetate (VAc) in 18 different solvents were theoretically computed at Density Function Theory (DFT) B3LYP/6-311G* level based on Polarizable Continuum Model (PCM) and experimentally recorded by FT-IR spectroscopy. The solvent-induced long-range bulk electrostatic solvation free energies of VAc (ΔGelec) were calculated by the SMD model. The Cdbnd O stretching vibration frequencies of VAc were utilized as a measure of the chemical reactivities of the Cdbnd C group in VAc. The calculated and experimental Cdbnd O stretching vibration frequencies of VAc (νcal(Cdbnd O) and νexp(Cdbnd O)) were correlated with empirical solvent parameters including the KBM equation, the Swain equation and the linear solvation energy relationships (LSER). Through ab initio calculation, assignments of the two Cdbnd O absorption bands of VAc in alcohol solvents were achieved. The PCM, SMD and ab initio calculation offered supporting evidence to explain the FT-IR experimental observations from differing aspects.

A combined experimental and DFT investigation of disazo dye having pyrazole skeleton

NASA Astrophysics Data System (ADS)

Şener, Nesrin; Bayrakdar, Alpaslan; Kart, Hasan Hüseyin; Şener, İzzet

2017-02-01

Disazo dye containing pyrazole skeleton has been synthesized. The structure of the dye has been confirmed by using FT-IR, 1H NMR, 13C NMR, HRMS spectral technique and elemental analysis. The molecular geometry and infrared spectrum are also calculated by the Density Functional Theory (DFT) employing B3LYP level with 6-311G (d,p) basis set. The chemical shifts calculation for 1H NMR of the title molecule is done by using by Gauge-Invariant Atomic Orbital (GIAO) method by utilizing the same basis sets. The total density of state, the partial density of state and the overlap population density of state diagram analysis are done via Gauss Sum 3.0 program. Frontier molecular orbitals such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and molecular electrostatic potential surface on the title molecule are predicted for various intramolecular interactions that are responsible for the stabilization of the molecule. The experimental results and theoretical values have been compared.

Excitation energies from particle-particle random phase approximation with accurate optimized effective potentials

NASA Astrophysics Data System (ADS)

Jin, Ye; Yang, Yang; Zhang, Du; Peng, Degao; Yang, Weitao

2017-10-01

The optimized effective potential (OEP) that gives accurate Kohn-Sham (KS) orbitals and orbital energies can be obtained from a given reference electron density. These OEP-KS orbitals and orbital energies are used here for calculating electronic excited states with the particle-particle random phase approximation (pp-RPA). Our calculations allow the examination of pp-RPA excitation energies with the exact KS density functional theory (DFT). Various input densities are investigated. Specifically, the excitation energies using the OEP with the electron densities from the coupled-cluster singles and doubles method display the lowest mean absolute error from the reference data for the low-lying excited states. This study probes into the theoretical limit of the pp-RPA excitation energies with the exact KS-DFT orbitals and orbital energies. We believe that higher-order correlation contributions beyond the pp-RPA bare Coulomb kernel are needed in order to achieve even higher accuracy in excitation energy calculations.

Pressure-induced Lifshitz and structural transitions in NbAs and TaAs: experiments and theory.

PubMed

Gupta, Satyendra Nath; Singh, Anjali; Pal, Koushik; Muthu, D V S; Shekhar, C; Elghazali, Moaz A; Naumov, Pavel G; Medvedev, Sergey A; Felser, C; Waghmare, U V; Sood, A K

2018-05-10

High pressure Raman, resistivity and synchrotron x-ray diffraction studies on Weyl semimetals NbAs and TaAs have been carried out along with density functional theoretical (DFT) analysis to explain pressure induced structural and electronic topological phase transitions. The frequencies of first order Raman modes harden with increasing pressure, exhibiting a slope change at [Formula: see text] GPa for NbAs and [Formula: see text] GPa for TaAs. The resistivities of NbAs and TaAs exhibit a minimum at pressures close to these transition pressures and also a change in the bulk modulus is observed. Our first-principles calculations reveal that the transition is associated with an electronic Lifshitz transition at [Formula: see text] for NbAs while it is a structural phase transition from body centered tetragonal to hexagonal phase at [Formula: see text] for TaAs. Further, our DFT calculations show a structural phase transition at 24 GPa from body centered tetragonal phase to hexagonal phase.

Unusual Complex Formation and Chemical Reaction of Haloacetate Anion on the Exterior Surface of Cucurbit[6]uril in the Gas Phase

NASA Astrophysics Data System (ADS)

Choi, Tae Su; Ko, Jae Yoon; Heo, Sung Woo; Ko, Young Ho; Kim, Kimoon; Kim, Hugh I.

2012-10-01

Noncovalent interactions of cucurbit[6]uril (CB[6]) with haloacetate and halide anions are investigated in the gas phase using electrospray ionization ion mobility mass spectrometry. Strong noncovalent interactions of monoiodoacetate, monobromoacetate, monochloroacetate, dichloroacetate, and trichloroacetate on the exterior surface of CB[6] are observed in the negative mode electrospray ionization mass spectra. The strong binding energy of the complex allows intramolecular SN2 reaction of haloacetate, which yields externally bound CB[6]-halide complex, by collisional activation. Utilizing ion mobility technique, structures of exteriorly bound CB[6] complexes of haloacetate and halide anions are confirmed. Theoretically determined low energy structures using density functional theory (DFT) further support results from ion mobility studies. The DFT calculation reveals that the binding energy and conformation of haloacetate on the CB[6] surface affect the efficiency of the intramolecular SN2 reaction of haloacetate, which correlate well with the experimental observation.

The comparison of approaches to the solid-state NMR-based structural refinement of vitamin B1 hydrochloride and of its monohydrate

NASA Astrophysics Data System (ADS)

Czernek, Jiří; Pawlak, Tomasz; Potrzebowski, Marek J.; Brus, Jiří

2013-01-01

The 13C and 15N CPMAS SSNMR measurements were accompanied by the proper theoretical description of the solid-phase environment, as provided by the density functional theory in the pseudopotential plane-wave scheme, and employed in refining the atomic coordinates of the crystal structures of thiamine chloride hydrochloride and of its monohydrate. Thus, using the DFT functionals PBE, PW91 and RPBE, the SSNMR-consistent solid-phase structures of these compounds are derived from the geometrical optimization, which is followed by an assessment of the fits of the GIPAW-predicted values of the chemical shielding parameters to their experimental counterparts.

A theoretical investigation on bio-transformation of third generation anti-cancer drug Heptaplatin and its interaction with DNA purine bases

NASA Astrophysics Data System (ADS)

Reddy B., Venkata P.; Mukherjee, Subhajit; Mitra, Ishani; Moi, Sankar Ch.

2017-12-01

Heptaplatin is an approved platinum based cytostatic drug for the treatment of gastric cancers. The hydrolytic bio-transformation of Heptaplatin and the platination processes of guanine (G) and adenine (A) with resulting mono and di-aquated species of Heptaplatin have been investigated using density functional theory (DFT) combined with the conductor like dielectric continuum model (CPCM) approach, to spotlight the drug activation energy profiles and their binding mechanisms. The stationary points on the potential energy surfaces were fully optimized and characterized. The mono-functional binding of Heptaplatin, guanine as target over adenine due to electronic factors and more favorable hydrogen-bonds pattern.

Application of Density Functional Theory to Systems Containing Metal Atoms

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

1997-01-01

The accuracy of density functional theory (DFT) for problems involving metal atoms is considered. The DFT results are compared with experiment as well as results obtained using the coupled cluster approach. The comparisons include geometries, frequencies, and bond energies. The systems considered include MO2, M(OH)+(sub n), MNO+, and MCO+(sub 2). The DFT works well for frequencies and geometries, even in cases with symmetry breaking; however, some examples have been found where the symmetry breaking is quite severe and the DFT methods do not work well. The calculation of bond energies is more difficult and examples of the successes as well as failures of DFT will be given.

A complete computational and spectroscopic study of 2-bromo-1, 4-dichlorobenzene - A frequently used benzene derivative

NASA Astrophysics Data System (ADS)

Vennila, P.; Govindaraju, M.; Venkatesh, G.; Kamal, C.; Mary, Y. Sheena; Panicker, C. Yohannan; Kaya, S.; Armaković, Stevan; Armaković, Sanja J.

2018-01-01

The coupled experimental and theoretical vibrational investigation of 2-bromo-1, 4-dichlorobenzene (BDB) molecule has been carried out and they have been duly compared with standard values in order to produce the reliability of the results. Results of DFT analysis carried out using B3LYP functional with 6-31 + G/6-311++G (d,p) basis set revealed that BDB has higher electronic density. The molecular geometry, 13C &1H Nuclear Magnetic Resonance (NMR), Natural Bond Orbital (NBO) and Natural Atomic Charge analyses have been obtained by DFT calculations. Nonlinear optical (NLO) properties, quantum chemical descriptors and first order hyperpolarizability have been calculated. In addition, Local reactivity properties reflected through average local ionization energies (ALIE), Fukui functions and bond dissociation energies have also been investigated. Besides investigation of docking properties, molecular dynamics simulations were also taken in account with a view to identify atoms that have relatively important interactions with water molecules. The title compound forms a stable complex with isopentenylpyrophosphate transferase with a binding affinity value as -4.6 kCal./Mol. and shows inhibitory activity against isopentenylpyrophosphate transferase.

Phytochemical, spectroscopic and density functional theory study of Diospyrin, and non-bonding interactions of Diospyrin with atmospheric gases

NASA Astrophysics Data System (ADS)

Fazl-i-Sattar; Ullah, Zakir; Ata-ur-Rahman; Rauf, Abdur; Tariq, Muhammad; Tahir, Asif Ali; Ayub, Khurshid; Ullah, Habib

2015-04-01

Density functional theory (DFT) and phytochemical study of a natural product, Diospyrin (DO) have been carried out. A suitable level of theory was developed, based on correlating the experimental and theoretical data. Hybrid DFT method at B3LYP/6-31G (d,p) level of theory is employed for obtaining the electronic, spectroscopic, inter-molecular interaction and thermodynamic properties of DO. The exact structure of DO is confirmed from the nice validation of the theory and experiment. Non-covalent interactions of DO with different atmospheric gases such as NH3, CO2, CO, and H2O were studied to find out its electroactive nature. The experimental and predicted geometrical parameters, IR and UV-vis spectra (B3LYP/6-31+G (d,p) level of theory) show excellent correlation. Inter-molecular non-bonding interaction of DO with atmospheric gases is investigated through geometrical parameters, electronic properties, charge analysis, and thermodynamic parameters. Electronic properties include, ionization potential (I.P.), electron affinities (E.A.), electrostatic potential (ESP), density of states (DOS), HOMO, LUMO, and band gap. All these characterizations have corroborated each other and confirmed the presence of non-covalent nature in DO with the mentioned gases.

Molecular structure, Hirshfeld surface analysis, theoretical investigations and nonlinear optical properties of a novel crystalline chalcone derivative: (E)-1-(5-bromothiophen-2-yl)-3-(p-tolyl)prop-2-en-1-one

NASA Astrophysics Data System (ADS)

Pramodh, B.; Lokanath, N. K.; Naveen, S.; Naresh, P.; Ganguly, S.; Panda, J.

2018-06-01

In the present work, the crystal structure of a novel chalcone derivative, (E)-1-(5-bromothiophen-2-yl)-3-(p-tolyl) prop-2-en-1-one has been confirmed by X-ray diffraction studies. Hirshfeld surface analysis was carried out to explore the intermolecular interactions. From the Hirshfeld surface analysis it was observed that H⋯H (26.7%) and C⋯H (26.3%) are the major contributors to the intermolecular interactions which stabilizes the crystal structure. The coordinates were optimized using the density functional theory (DFT) calculations using B3LYP hybrid functions with 6-31G(d) basis set. The structural parameters obtained from XRD studies compliment with those calculated using DFT calculations. The HOMO and LUMO energy gap was found to be 4.1778 eV. The molecular electrostatic potential (MEP) was plotted to identify the possible reactions sites of the molecule. Further, non-linear optical (NLO) properties were investigated by calculating hyperpolarizabilities which indicate that the title compound would be a potential candidate for the NLO applications.

Theoretical studies of structure and selectivity of 5-methyl-4-(2-thiazolylazo) resorcinol as a sensor for metal ions: DFT calculation

NASA Astrophysics Data System (ADS)

Thaomola, Sukhontip; Sompech, Supachai

2018-05-01

The global minimum optimized structures of the free sensor 5-methyl-4-(2-thiazolylazo) resorcinol (5-Me-TAR) and 5-Me-TAR-Cu2+ complexes in the gas phase have been investigated by using Density Functional Theory (DFT) with the def2-TZVP basis set. To compare the selectivity of 5-Me-TAR for metal ions, the binding energy of 5-Me-TAR with various metal ions (Na+, K+, Mg2+, Ca2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Pd2+, Cd2+ and Hg2+) were calculated at the same level as the theory. Binding energy values of most transition metal ions are lower than alkaline earth metal ions and alkali metal ions, respectively. The 5-Me-TAR sensor shows the highest selectivity with the Cu2+ ion. Moreover, Dependent Density Functional Theory (TDDFT) results confirm that the 5-Me-TAR-Cu2+ complex is stabilized by the sensor to metal charge transfer process. The computational studies suggested that the 5-Me-TAR is suitable for Cu2+ ion detection sensor development.

Redox reaction characteristics of riboflavin: a fluorescence spectroelectrochemical analysis and density functional theory calculation.

PubMed

Chen, Wei; Chen, Jie-Jie; Lu, Rui; Qian, Chen; Li, Wen-Wei; Yu, Han-Qing

2014-08-01

Riboflavin (RF), the primary redox active component of flavin, is involved in many redox processes in biogeochemical systems. Despite of its wide distribution and important roles in environmental remediation, its redox behaviors and reaction mechanisms in hydrophobic sites remain unclear yet. In this study, spectroelectrochemical analysis and density functional theory (DFT) calculation were integrated to explore the redox behaviors of RF in dimethyl sulfoxide (DMSO), which was used to create a hydrophobic environment. Specifically, cyclic voltafluorometry (CVF) and derivative cyclic voltafluorometry (DCVF) were employed to track the RF concentration changing profiles. It was found that the reduction contained a series of proton-coupled electron transfers dependent of potential driving force. In addition to the electron transfer-chemical reaction-electron transfer process, a disproportionation (DISP1) process was also identified to be involved in the reduction. The redox potential and free energy of each step obtained from the DFT calculations further confirmed the mechanisms proposed based on the experimental results. The combination of experimental and theoretical approaches yields a deep insight into the characteristics of RF in environmental remediation and better understanding about the proton-coupled electron transfer mechanisms. Copyright © 2014 Elsevier B.V. All rights reserved.

Combined ab initio and density functional study on polaron to bipolaron transitions in oligophenyls and oligothiophenes

NASA Astrophysics Data System (ADS)

Irle, Stephan; Lischka, Hans

1997-08-01

Ab initio self-consistent-field (SCF), two-configuration SCF (TCSCF), and density functional theory (DFT) calculations on the charge-transfer complexes of doubly Li/Cl-doped oligothiophenes and oligo(p-phenyls) and on respective charged systems without counterions have been carried out in order to study polaron to bipolaron transitions. Oligomer chains up to octamers and the ring structures cyclo-dodecathiophene and cyclo-dodeca(p-phenyl) have been investigated. Special attention is paid to the open-shell biradical character of two isolated polaronic defects. It is found that the TCSCF and the spin-unrestricted DFT methods can be successfully applied. A bipolaron structure is obtained when the doping atoms are located on neighboring rings and when there is one undoped ring separating the two doped ones. If there are two or more undoped rings in between a two-polaron configuration (biradical) is found. The bipolaron system is calculated to be more stable than the two-polaron case when counterions are taken into account. The stabilities are reversed if the bare, doubly-charged systems are considered. A theoretical estimate for the barrier height of the polaron to bipolaron transition is given using model reaction coordinates.

Molecular structure, vibrational spectra, NBO, UV and first order hyperpolarizability, analysis of 4-Chloro-dl-phenylalanine by density functional theory.

PubMed

Govindarasu, K; Kavitha, E

2014-12-10

The Fourier transform infrared (4000-400cm(-1)) and Fourier transform Raman (3500-50cm(-1)) spectra of 4-Chloro-dl-phenylalanine (4CLPA) were recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers were investigated with the help of density functional theory (DFT) method using B3LYP/6-31G(d,p) as basis set. The observed vibrational wavenumbers were compared with the calculated results. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. Predicted electronic absorption spectra from TD-DFT calculation have been analyzed comparing with the UV-Vis (200-800nm) spectrum. The effects of chlorine and ethylene group substituent in benzene ring in the vibrational wavenumbers have been analyzed. The HOMO-LUMO energy gap explains the charge interaction taking place within the molecule. The first order hyperpolarizability (β0) and related properties (β, α0 and Δα) of 4CLPA were calculated. The Chemical reactivity and chemical potential of 4CLPA is calculated. In addition, molecular electrostatic potential (MEP), frontier molecular orbital (FMO) analysis were investigated using theoretical calculations. Published by Elsevier B.V.

Persistence of Mixed and Non-intermediate Valence in the High-Pressure Structure of Silver(I,III) Oxide, AgO: A Combined Raman, X-ray Diffraction (XRD), and Density Functional Theory (DFT) Study.

PubMed

Grzelak, Adam; Gawraczyński, Jakub; Jaroń, Tomasz; Somayazulu, Maddury; Derzsi, Mariana; Struzhkin, Viktor; Grochala, Wojciech

2017-05-15

The X-ray diffraction data collected up to ca. 56 GPa and the Raman spectra measured up to 74.8 GPa for AgO, or Ag I Ag III O 2 , which is a prototypical mixed valence (disproportionated) oxide, indicate that two consecutive phase transitions occur: the first-order phase transition occurs between 16.1 GPa and 19.7 GPa, and a second-order phase transition occurs at ca. 40 GPa. All polymorphic forms host the square planar [Ag III O 4 ] units typical of low-spin Ag III . The disproportionated Imma form persists at least up to 74.8 GPa, as indicated by Raman spectra. Theoretical hybrid density functional theory (DFT) calculations show that the first-order transition is phonon-driven. AgO stubbornly remains disproportionated up to at least 100 GPa-in striking contrast to its copper analogue-and the fundamental band gap of AgO is ∼0.3 eV at this pressure and is weakly pressure-dependent. Metallization of AgO is yet to be achieved.

Theory of copper impurities in ZnO

NASA Astrophysics Data System (ADS)

Lyons, John; Alkauskas, Audrius; Janotti, Anderson; van de Walle, Chris G.

Due to its connection to deep luminescence signals and its potential use as an acceptor dopant, copper has been one the most studied impurities in ZnO. From experiment, copper incorporating on the Zn site (CuZn) is known to lead to an acceptor level residing near the conduction band of ZnO, making CuZn an exceedingly deep acceptor. CuZn in ZnO has also long been linked with broad 2.4 eV green luminescence (GL) signals. In this work we explore the electrical and optical properties of Cu in ZnO using density functional theory (DFT). Due to the limitations of traditional forms of DFT, an accurate theoretical description of the electrical and optical properties of such deep centers has been difficult to achieve. Here we employ a screened hybrid density functional (HSE) to calculate the properties of Cu in ZnO. We determine the thermodynamic transition levels associated with CuZn in ZnO as well as the associated luminescence lineshapes of characteristic optical transitions. We find that HSE-calculated optical transitions are in close agreement with experimental studies. This work was supported in part by NSF and by ARO.

FT-IR, FT-Raman spectra and DFT calculations of melaminium perchlorate monohydrate.

PubMed

Kanagathara, N; Marchewka, M K; Drozd, M; Renganathan, N G; Gunasekaran, S; Anbalagan, G

2013-08-01

Melaminium perchlorate monohydrate (MPM), an organic material has been synthesized by slow solvent evaporation method at room temperature. Powder X-ray diffraction analysis confirms that MPM crystal belongs to triclinic system with space group P-1. FTIR and FT Raman spectra are recorded at room temperature. Functional group assignment has been made for the melaminium cations and perchlorate anions. Vibrational spectra have also been discussed on the basis of quantum chemical density functional theory (DFT) calculations using Firefly (PC GAMESS) version 7.1 G. Vibrational frequencies are calculated and scaled values are compared with experimental values. The assignment of the bands has been made on the basis of the calculated PED. The Mulliken charges, HOMO-LUMO orbital energies are analyzed directly from Firefly program log files and graphically illustrated. HOMO-LUMO energy gap and other related molecular properties are also calculated. The theoretically constructed FT-IR and FT-Raman spectra of MPM coincide with the experimental one. The chemical structure of the compound has been established by (1)H and (13)C NMR spectra. No detectable signal was observed during powder test for second harmonic generation. Copyright © 2013 Elsevier B.V. All rights reserved.

Assessment of amide I spectroscopic maps for a gas-phase peptide using IR-UV double-resonance spectroscopy and density functional theory calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carr, J. K.; Roy, S.; Skinner, J. L.

2014-06-14

The spectroscopy of amide I vibrations has become a powerful tool for exploring protein structure and dynamics. To help with spectral interpretation, it is often useful to perform molecular dynamics (MD) simulations. To connect spectroscopic experiments to simulations in an efficient manner, several researchers have proposed “maps,” which relate observables in classical MD simulations to quantum spectroscopic variables. It can be difficult to discern whether errors in the theoretical results (compared to experiment) arise from inaccuracies in the MD trajectories or in the maps themselves. In this work, we evaluate spectroscopic maps independently from MD simulations by comparing experimental andmore » theoretical spectra for a single conformation of the α-helical model peptide Ac-Phe-(Ala){sub 5}-Lys-H{sup +} in the gas phase. Conformation-specific experimental spectra are obtained for the unlabeled peptide and for several singly and doubly {sup 13}C-labeled variants using infrared-ultraviolet double-resonance spectroscopy, and these spectra are found to be well-modeled by density functional theory (DFT) calculations at the B3LYP/6-31G** level. We then compare DFT results for the deuterated and {sup 13}C{sup 18}O-labeled peptide with those from spectroscopic maps developed and used previously by the Skinner group. We find that the maps are typically accurate to within a few cm{sup −1} for both frequencies and couplings, having larger errors only for the frequencies of terminal amides.« less

What Density Functional Theory could do for Quantum Information

NASA Astrophysics Data System (ADS)

Mattsson, Ann

2015-03-01

The Hohenberg-Kohn theorem of Density Functional Theory (DFT), and extensions thereof, tells us that all properties of a system of electrons can be determined through their density, which uniquely determines the many-body wave-function. Given access to the appropriate, universal, functionals of the density we would, in theory, be able to determine all observables of any electronic system, without explicit reference to the wave-function. On the other hand, the wave-function is at the core of Quantum Information (QI), with the wave-function of a set of qubits being the central computational resource in a quantum computer. While there is seemingly little overlap between DFT and QI, reliance upon observables form a key connection. Though the time-evolution of the wave-function and associated phase information is fundamental to quantum computation, the initial and final states of a quantum computer are characterized by observables of the system. While observables can be extracted directly from a system's wave-function, DFT tells us that we may be able to intuit a method for extracting them from its density. In this talk, I will review the fundamentals of DFT and how these principles connect to the world of QI. This will range from DFT's utility in the engineering of physical qubits, to the possibility of using it to efficiently (but approximately) simulate Hamiltonians at the logical level. The apparent paradox of describing algorithms based on the quantum mechanical many-body wave-function with a DFT-like theory based on observables will remain a focus throughout. The ultimate goal of this talk is to initiate a dialog about what DFT could do for QI, in theory and in practice. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Communication: Recovering the flat-plane condition in electronic structure theory at semi-local DFT cost

NASA Astrophysics Data System (ADS)

Bajaj, Akash; Janet, Jon Paul; Kulik, Heather J.

2017-11-01

The flat-plane condition is the union of two exact constraints in electronic structure theory: (i) energetic piecewise linearity with fractional electron removal or addition and (ii) invariant energetics with change in electron spin in a half filled orbital. Semi-local density functional theory (DFT) fails to recover the flat plane, exhibiting convex fractional charge errors (FCE) and concave fractional spin errors (FSE) that are related to delocalization and static correlation errors. We previously showed that DFT+U eliminates FCE but now demonstrate that, like other widely employed corrections (i.e., Hartree-Fock exchange), it worsens FSE. To find an alternative strategy, we examine the shape of semi-local DFT deviations from the exact flat plane and we find this shape to be remarkably consistent across ions and molecules. We introduce the judiciously modified DFT (jmDFT) approach, wherein corrections are constructed from few-parameter, low-order functional forms that fit the shape of semi-local DFT errors. We select one such physically intuitive form and incorporate it self-consistently to correct semi-local DFT. We demonstrate on model systems that jmDFT represents the first easy-to-implement, no-overhead approach to recovering the flat plane from semi-local DFT.

Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine

NASA Astrophysics Data System (ADS)

Srivastava, Santosh K.; Singh, Vipin B.

2013-11-01

Vibrational spectra and molecular structure of anhydrous caffeine have been systematically investigated by second order Moller-Plesset (MP2) perturbation theory and density functional theory (DFT) calculations. Vibrational assignments have been made and many previous ambiguous assignments in IR and Raman spectra are amended. The calculated DFT frequencies and intensities at B3LYP/6-311++G(2d,2p) level, were found to be in better agreement with the experimental values. It was found that DFT with B3LYP functional predicts harmonic vibrational wave numbers more close to experimentally observed value when it was performed on MP2 optimized geometry rather than DFT geometry. The calculated TD-DFT vertical excitation electronic energies of the valence excited states of anhydrous caffeine are found to be in consonance to the experimental absorption peaks.

Application of the bounds-analysis approach to arsenic and gallium antisite defects in gallium arsenide

DOE PAGES

Wright, A. F.; Modine, N. A.

2015-01-23

The As antisite in GaAs (AsGa) has been the subject of numerous experimental and theoretical studies. Recent density-functional-theory (DFT) studies report results in good agreement with experimental data for the +2, +1, and 0 charge states of the stable EL2 structure, the 0 charge state of the metastable EL2* structure, and the activation energy to transform from EL2* to EL2 in the 0 charge state. However, these studies did not report results for EL2* in the -1 charge state. In this paper, we report new DFT results for the +2, +1, 0, and -1 charge states of AsGa, obtained usingmore » a semilocal exchange-correlation functional and interpreted using a bounds-analysis approach. In good agreement with experimental data, we find a -1/0 EL2* level 0.06 eV below the conduction-band edge and an activation energy of 0.05 eV to transform from EL2* to EL2 in the -1 charge state. While the Ga antisite in GaAs (GaAs) has not been studied as extensively as AsGa, experimental studies report three charge states (-2, -1, 0) and two levels (-2/-1, -1/0) close to the valence-band edge. Recent DFT studies report the same charge states, but the levels are found to be well-separated from the valence-band edge. To resolve this disagreement, we performed new DFT calculations for GaAs and interpreted them using a bounds analysis. The analysis identified the -1 and 0 charge states as hole states weakly bound to a highly-localized -2 charge state. Moreover, the -2/-1, -1/0 levels were found to be near the valence-band edge, in good agreement with the experimental data.« less

Adsorption of alanine with heteroatom substituted fullerene for solar cell application: A DFT study.

PubMed

Dheivamalar, S; Sugi, L; Ravichandran, K; Sriram, S

2018-09-05

C 20 is the most important fullerene cage and alanine is the simplest representation of a backbone unit of the protein. The absorption feasibility of alanine molecule in the Si-doped C 20 and B-doped C 20 fullerenes has been studied based on calculated electronic properties of fullerenes using density functional theory (DFT). In this work, we explore the ability of Si-doped C 20 , B-doped C 20 fullerene to interact with alanine at the DFT-B3LYP/6-31G, RHF level of theory. We find that noticeable structural change takes place in C 20 when one of its carbon is substituted with Si or B. The molecular geometry, electronic properties and vibrational analysis have also been performed on the title compounds. The NMR study reveals the aromaticity of the pure and doped fullerene compounds. Stability of the doped fullerene - alanine compound arises from hyper conjugative interactions. It leads to one of the major property of bioactivity, charge transfer and delocalization of charge and this properties has been analyzed using Natural Bond Orbital (NBO) analysis. The energy gap of the doped fullerene reveals that there is a decrease in the size of energy gap significantly, making them more reactive as compared to C 20 fullerene. Theoretical studies of the electronic spectra by using time - dependent density functional theory (TD-DFT) method were helpful to interpret the observed electronic transition state. We aim to optimize the performance of the solar cells by altering the frontier orbital energy gaps. Considering all studied properties, it may be inferred that the applicability of C 20 fullerene as the non-linear optical (NLO) material and its NLO property would increase on doping fullerene with Si and B atom. Specifically C 19 Si would be better among them. Copyright © 2018. Published by Elsevier B.V.

Synthesis, spectroscopic characterization and crystallographic behavior of a biologically relevant novel indole-fused heterocyclic compound - Experimental and theoretical (DFT) studies

NASA Astrophysics Data System (ADS)

Sharma, Sakshi; Brahmachari, Goutam; Banerjee, Bubun; Nurjamal, Khondekar; Kumar, Abhishek; Srivastava, Ambrish Kumar; Misra, Neeraj; Pandey, Sarvesh Kumar; Rajnikant; Gupta, Vivek K.

2016-08-01

The present communication deals with the eco-friendly synthesis, spectral properties and X-ray crystal structure of an indole derivative - Ethyl 2'-amino-3'-cyano-6'-methyl-5-nitro-2-oxospiro [indoline-3,4'-pyran]-5'-carboxylate. The title compound was synthesized in 87% yield. The crystal structure of the molecule is stabilized by intermolecular Nsbnd H … N, Nsbnd H … O and Csbnd H … π interactions. The molecule is organized in the crystal lattice forming sheet like structure. To interpret the experimental data, ab initio computations of the vibrational frequencies were carried out using the Gaussian 09 program followed by the full optimizations done using Density Functional Theory (DFT) at B3LYP/6-31 + G(d,p) level. The combined use of experiments and computations allowed a firm assignment of the majority of observed bands for the compound. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with frontier orbital gap were presented. The electronic and charge transfer properties have been explained on the basis of highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs) and density of states (DOS). From the optimized geometry of the molecule, molecular electrostatic potential (MEP) distribution, frontier molecular orbitals (FMOs) of the title compound have been calculated in the ground state theoretically. The theoretical results showed good agreement with the experimental values. First hyperpolarizability values have been calculated to describe the nonlinear optical (NLO) property of the synthesized compound.

Electronic spectroscopy of HRe(CO) 5: a CASSCF/CASPT2 and TD-DFT study

NASA Astrophysics Data System (ADS)

Bossert, J.; Ben Amor, N.; Strich, A.; Daniel, C.

2001-07-01

The low-lying excited states of HRe(CO) 5 have been calculated at the CASSCF/CASPT2 and TD-DFT level of theory using relativistic effective core potentials (ECP) or ab initio model potentials (AIMP). The theoretical absorption spectrum is compared to the experimental one. Despite the similarity between the experimental absorption spectra of HMn(CO) 5 and HRe(CO) 5 in the UV/visible energy domain it is shown that the assignment differs significantly between the two molecules. The low-lying excited states of HRe(CO) 5 correspond to 5d→π *CO excitations whereas the spectrum of HMn(CO) 5 consists mainly of 3d→3d and 3d→ σ*Mn-H excitations. If the CASPT2 and TD-DFT results are quite comparable for the lowest excited states, the upper part assignment is more problematic with the TD-DFT method.

Ferrocenyl-substituted dinuclear Cu(II) complex: Synthesis, spectroscopy, electrochemistry, DFT calculations and catecholase activity

NASA Astrophysics Data System (ADS)

Emirik, Mustafa; Karaoğlu, Kaan; Serbest, Kerim; Menteşe, Emre; Yilmaz, Ismail

2016-02-01

A new ferrocenyl-substituted heterocyclic hydrazide ligand and its Cu(II) complex were prepared. The DFT calculations were performed to determine the electronic and molecular structures of the title compounds. The electronic spectra were calculated by using time-dependent DFT method, and the transitions were correlated with the molecular orbitals of the compounds. The bands assignments of IR spectra were achieved in the light of the theoretical vibrational spectral data and total energy distribution values calculated at DFT/B3LYP/6-311++G(d,p) level. The redox behaviors of the ferrocene derivatives were investigated by cyclic voltammetry. The compounds show reversible redox couple assignable to Fc+/Fc couple. The copper(II) complex behaves as an effective catalyst towards oxidation of 3,5-di-tert-butylcatechol to its corresponding quinone derivative in DMF saturated with O2. The reaction follows Michaelis-Menten enzymatic reaction kinetics with turnover numbers 2.32 × 103.

An innovative method for the non-destructive identification of photodegradation products in solid state: 1H-14N NMR-NQR and DFT/QTAIM study of photodegradation of nifedipine (anti-hypertensive) to nitrosonifedipine (potential anti-oxidative).

PubMed

Latosińska, J N; Latosińska, M; Seliger, J; Zagar, V

2012-08-30

Stability of the antihypertensive drug nifedipine (NIF) has been studied experimentally in solid state by (1)H-(14)N NMR-NQR double resonance (NQDR) and theoretically by the Density Functional Theory (DFT). Photodegradation of NIF to its metabolite in vivo nitrosonifedipine, NO-NIF (antioxidative agent) upon long term daylight exposure was detected and the changes in the molecular structure of NIF were analysed. The photoconversion of NIF to NO-NIF in solid was found to be accompanied with the electron density redistribution at nitrogen sites (NH to N and NO(2) to NO) and proved to be successfully detected with identification of photoproducts by (1)H-(14)N NQDR and DFT methods. The increase in the e(2)qQ/h and η describing EFG tendency towards non-spherical symmetry was significantly greater upon the reduction of NO(2) site than upon hydrogen abstraction from NH site. The level of sensitivity of detection of the photodegradation product was about 1% of the original sample. The Quantum Theory of Atoms in Molecules (QTAIM) analysis has been found useful in predicting photoreactive sites in the molecules and finding the explanation of differences in reactivity between parent NIF and its photoproduct NO-NIF. Using NIF as a model, this study demonstrates the suitability of NQDR supported by DFT for non-destructive determination of the photodegradation products in solid state. Copyright © 2012 Elsevier B.V. All rights reserved.

Hydrogen bond strengthening between o-nitroaniline and formaldehyde in electronic excited states: A theoretical study

NASA Astrophysics Data System (ADS)

Yang, Juan; Li, An Yong

2018-06-01

To study the hydrogen bonds upon photoexcited, the time dependent density function method (TD DFT) was performed to investigate the excited state hydrogen bond properties of between o-nitroaniline (ONA) and formaldehyde (CH2O). The optimized structures of the complex and the monomers both in the ground state and the electronically excited states are calculated using DFT and TD DFT method respectively. Quantum chemical calculations of the electronic and vibrational absorption spectra are also carried out by TD DFT method at the different level. The complex ONA⋯CH2O forms the intramolecular hydrogen bond and intermolecular hydrogen bonds. Since the strength of hydrogen bonds can be measured by studying the vibrational absorption spectra of the characteristic groups on the hydrogen bonding acceptor and donor, it evidently confirms that the hydrogen bonds is strengthened in the S1/S2/T1 excited states upon photoexcitation. As a result, the hydrogen bonds cause that the CH stretch frequency of the proton donor CH2O has a blue shift, and the electron excitations leads to a frequency red shift of Ndbnd O and Nsbnd H stretch modes in the o-nitroaniline(ONA) and a small frequency blue shift of CH stretch mode in the formaldehyde(CH2O) in the S1 and S2 excited states. The excited states S1, S2 and T1 are locally excited states where only the ONA moiety is excited, but the CH2O moiety remains in its ground state.

Growth, structure, Hirshfeld surface and spectroscopic properties of 2-amino-4-hydroxy-6-methylpyrimidinium-2,3-pyrazinedicorboxylate single crystal

NASA Astrophysics Data System (ADS)

Faizan, Mohd; Alam, Mohammad Jane; Afroz, Ziya; Rodrigues, Vítor Hugo Nunes; Ahmad, Shabbir

2018-03-01

The present work is focused on the crystal structure, vibrational spectroscopy and DFT calculations of hydrogen bonded 2,3-pyrazinedicorboxylic acid and 2-amino-4-hydroxy-6-methylpyrimidine (PDCA-.AHMP+) crystal. The crystal structure has been determined using single crystal X-ray diffraction analysis which shows that the crystal belongs to monoclinic space group P21/n. The PDCA-.AHMP+ crystal has been characterized by FTIR, FT-Raman and FT-NMR spectroscopic techniques. The FTIR and FT-Raman spectra of the complex have unique spectroscopic feature as compared with those of the starting material to confirm salt formation. The theoretical vibrational studies have been performed to understand the modes of the vibrations of asymmetric unit of the complex by DFT methods. Hirschfeld surface and 2D fingerprint plots analyses were carried out to investigate the intermolecular interactions and its contribution in the building of PDCA-.AHMP+ crystal. The experimental and simulated 13C and 1H NMR studies have assisted in structural analysis of PDCA-.AHMP+ crystal. The electronic spectroscopic properties of the complex were explored by the experimental as well as theoretical electronic spectra simulated using TD-DFT/IEF-PCM method at B3LYP/6-311++G (d,p) level of theory. In addition, frontier molecular orbitals, molecular electrostatic potential map (MEP) and nonlinear optical (NLO) properties using DFT method have been also presented.

DFT and TD-DFT insights, photolysis and photocatalysis investigation of three dyes with similar structure under UV irradiation with and without TiO2 as a catalyst: Effect of adsorption, pH and light intensity

NASA Astrophysics Data System (ADS)

Bendjabeur, Seyfeddine; Zouaghi, Razika; Zouchoune, Bachir; Sehili, Tahar

2018-02-01

TiO2-mediated photocatalytic degradation of three triphenylmethane dyes (basic fuchsin, acid fuchsin and Gentian violet), was investigated in aqueous suspensions in the presence and the absence of titanium dioxide P25 Degussa as photocatalyst. The photodegradation process was investigated using UV-A (365 nm) and UV-C (254 nm) light alone and UV-A in the presence of TiO2·The effects of various operational parameters were investigated such as: the effect of adsorption in the dark, the influence of pH, the influence of irradiation wavelength and the effect of light intensity. The study of the effect of various parameters reveals that the photolysis of dyes increases with the increase of light intensity, the degradation rate under UV-C (254 nm) was found better than under UV-A 365 nm. The photocatalytic degradation was found to follow the same order of adsorption. The decolorization and the degradation kinetics were found to follow the pseudo-first-order kinetics. The mineralization of dye was found to follow the same order of disappearance as the photocatalytic degradation and depended directly to its functional groups and its number of carbons. Additionally, density functional theory (DFT) was applied for calculations of both electronic structure and spectroscopic properties of the studied compounds, where the obtained results of the three dyes show that the theoretical electronic spectra and the experimental UV-visible ones are similar in shapes, positions and intensities.

Electronic structure and optical properties of Cs2HgCl4: DFT calculations and X-ray photoelectron spectroscopy measurements

NASA Astrophysics Data System (ADS)

Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Parasyuk, O. V.; Fedorchuk, A. O.; Khyzhun, O. Y.

2016-10-01

A high-quality single crystal of cesium mercury tetrabromide, Cs2HgCl4, was synthesized by using the vertical Bridgman-Stockbarger method and its electronic structure was studied from both experimental and theoretical viewpoints. In particular, X-ray photoelectron spectra were measured for both pristine and Ar+ ion-bombarded Cs2HgCl4 single crystal surfaces. The present XPS measurements indicate that the Cs2HgCl4 single crystal surface is sensitive with respect to Ar+ ion-bombardment: such a treatment changes substantially its elemental stoichiometry. With the aim of exploring total and partial densities of states within the valence band and conduction band regions of the Cs2HgCl4 compound, band-structure calculations based on density functional theory (DFT) using the augmented plane wave + local orbitals (APW + lo) method as incorporated within the WIEN2k package are performed. The calculations indicate that the Cl 3p states are the principal contributors in the upper portion of the valence band, while the Hg 5d and Cs 5p states dominate in its lower portion. In addition, the calculations allow for concluding that the unoccupied Cl p and Hg s states are the main contributors to the bottom of the conduction band. Furthermore, main optical characteristics of Cs2HgCl4, namely dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity, are elucidated based on the DFT calculations.

Experimental and theoretical studies of the crystal structures of bis-isoxazole-bis-methylene dinitrate (BIDN) and bis-isoxazole tetramethylene tetranitrate (BITN) by x-ray crystallography and density functional theory

NASA Astrophysics Data System (ADS)

Taylor, Decarlos E.; Sausa, Rosario C.

2018-06-01

The determination of crystal structures plays an important role for model testing and validation, and understanding intra and intermolecular interactions that influence crystal packing. Here, we report the molecular structure of two recently synthesized energetic molecules, 3,3-bis-isoxazole-5,5‧-bis-methylene dinitrate (C8H6N4O8, BIDN) and bis-isoxazole tetramethylene tetranitrate (C10H8N6O14, BITN) determined by single crystal x-ray diffraction and solid state density functional theory (DFT). BIDN is composed of two planar alkyl nitrate groups (r.m.s deviation = 0.0004 (1) Å) bonded to two planar azole rings (r.m.s deviation = 0.001 (1) Å, whereas BITN is composed of four planar alkyl nitrate groups (average r.m.s deviation = 0.002 (1) Å) bonded to two planar azole rings (average r.m.s deviation = 0.002 (1) Å). The theoretical calculations predict very well the planarity of both the alkyl nitrate groups and rings for both compounds. Furthermore, they predict well the bond lengths and angles of both molecules with mean deviation values of 0.018 Å (BIDN) and 0.017 Å (BITN) and 0.481° (BIDN) and 0.747° (BITN). Overall, the DFT determined torsion angles agree well with those determined experimentally for both BIDN (average deviation = 1.139°) and BITN (average deviation = 0.604°). The theoretical cell constant values are in excellent agreement with those determined experimentally for both molecules, with the BIDN a cell value and β angle showing the largest deviation, 2.1% and -1.3%, respectively. Contacts between the atoms N and H dominate the intermolecular interactions of BIDN, whereas contacts involving the atoms O and H dominate the BITN intermolecular interactions. Electrostatic potential calculations at the B3LYP/6-31G* level reveal BIDN exhibits a lower sensitivity to impact compared to BITN.

The phase diagram and transport properties of MgO from theory and experiment

NASA Astrophysics Data System (ADS)

Shulenburger, Luke

2013-06-01

Planetary structure and the formation of terrestrial planets have received tremendous interest due to the discovery of so called super-earth exoplanets. MgO is a major constituent of Earth's mantle, the rocky cores of gas giants and is a likely component of the interiors of many of these exoplanets. The high pressure - high temperature behavior of MgO directly affects equation of state models for planetary structure and formation. In this work, we examine MgO under extreme conditions using experimental and theoretical methods to determine its phase diagram and transport properties. Using plate impact experiments on Sandia's Z facility the solid-solid phase transition from B1 to B2 is clearly determined. The melting transition, on the other hand, is subtle, involving little to no signal in us-up space. Theoretical work utilizing density functional theory (DFT) provides a complementary picture of the phase diagram. The solid-solid phase transition is identified through a series of quasi-harmonic phonon calculations and thermodynamic integration, while the melt boundary is found using phase coexistence calculations. One issue of particular import is the calculation of reflectivity along the Hugoniot and the influence of the ionic structure on the transport properties. Particular care is necessary because of the underestimation of the band gap and attendant overestimation of transport properties due to the use of semi-local density functional theory. We will explore the impact of this theoretical challenge and its potential solutions in this talk. The integrated use of DFT simulations and high-accuracy shock experiments together provide a comprehensive understanding of MgO under extreme conditions. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE's National Nuclear Security Administration under contract DE-AC04-94AL85000.

The force distribution probability function for simple fluids by density functional theory.

PubMed

Rickayzen, G; Heyes, D M

2013-02-28

Classical density functional theory (DFT) is used to derive a formula for the probability density distribution function, P(F), and probability distribution function, W(F), for simple fluids, where F is the net force on a particle. The final formula for P(F) ∝ exp(-AF(2)), where A depends on the fluid density, the temperature, and the Fourier transform of the pair potential. The form of the DFT theory used is only applicable to bounded potential fluids. When combined with the hypernetted chain closure of the Ornstein-Zernike equation, the DFT theory for W(F) agrees with molecular dynamics computer simulations for the Gaussian and bounded soft sphere at high density. The Gaussian form for P(F) is still accurate at lower densities (but not too low density) for the two potentials, but with a smaller value for the constant, A, than that predicted by the DFT theory.

Calculation of the exchange coupling constants of copper binuclear systems based on spin-flip constricted variational density functional theory.

PubMed

Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

2011-11-14

We have recently developed a methodology for the calculation of exchange coupling constants J in weakly interacting polynuclear metal clusters. The method is based on unrestricted and restricted second order spin-flip constricted variational density functional theory (SF-CV(2)-DFT) and is here applied to eight binuclear copper systems. Comparison of the SF-CV(2)-DFT results with experiment and with results obtained from other DFT and wave function based methods has been made. Restricted SF-CV(2)-DFT with the BH&HLYP functional yields consistently J values in excellent agreement with experiment. The results acquired from this scheme are comparable in quality to those obtained by accurate multi-reference wave function methodologies such as difference dedicated configuration interaction and the complete active space with second-order perturbation theory. © 2011 American Institute of Physics

Many-Body Spectral Functions from Steady State Density Functional Theory.

PubMed

Jacob, David; Kurth, Stefan

2018-03-14

We propose a scheme to extract the many-body spectral function of an interacting many-electron system from an equilibrium density functional theory (DFT) calculation. To this end we devise an ideal scanning tunneling microscope (STM) setup and employ the recently proposed steady-state DFT formalism (i-DFT) which allows one to calculate the steady current through a nanoscopic region coupled to two biased electrodes. In our setup, one of the electrodes serves as a probe ("STM tip"), which is weakly coupled to the system we want to measure. In the ideal STM limit of vanishing coupling to the tip, the system is restored to quasi-equilibrium and the normalized differential conductance yields the exact equilibrium many-body spectral function. Calculating this quantity from i-DFT, we derive an exact relation expressing the interacting spectral function in terms of the Kohn-Sham one. As illustrative examples, we apply our scheme to calculate the spectral functions of two nontrivial model systems, namely the single Anderson impurity model and the Constant Interaction Model.

Analytical gradients for subsystem density functional theory within the slater-function-based amsterdam density functional program.

PubMed

Schlüns, Danny; Franchini, Mirko; Götz, Andreas W; Neugebauer, Johannes; Jacob, Christoph R; Visscher, Lucas

2017-02-05

We present a new implementation of analytical gradients for subsystem density-functional theory (sDFT) and frozen-density embedding (FDE) into the Amsterdam Density Functional program (ADF). The underlying theory and necessary expressions for the implementation are derived and discussed in detail for various FDE and sDFT setups. The parallel implementation is numerically verified and geometry optimizations with different functional combinations (LDA/TF and PW91/PW91K) are conducted and compared to reference data. Our results confirm that sDFT-LDA/TF yields good equilibrium distances for the systems studied here (mean absolute deviation: 0.09 Å) compared to reference wave-function theory results. However, sDFT-PW91/PW91k quite consistently yields smaller equilibrium distances (mean absolute deviation: 0.23 Å). The flexibility of our new implementation is demonstrated for an HCN-trimer test system, for which several different setups are applied. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Density functional theory and phytochemical study of 8-hydroxyisodiospyrin

NASA Astrophysics Data System (ADS)

Ullah, Zakir; Ata-ur-Rahman; Fazl-i-Sattar; Rauf, Abdur; Yaseen, Muhammad; Hassan, Waseem; Tariq, Muhammad; Ayub, Khurshid; Tahir, Asif Ali; Ullah, Habib

2015-09-01

Comprehensive theoretical and experimental studies of a natural product, 8-hydroxyisodiospyrin (HDO) have been carried out. Based on the correlation of experimental and theoretical data, an appropriate computational model was developed for obtaining the electronic, spectroscopic, and thermodynamic parameters of HDO. First of all, the exact structure of HDO is confirmed from the nice correlation of theory and experiment, prior to determination of its electroactive nature. Hybrid density functional theory (DFT) is employed for all theoretical simulations. The experimental and predicted IR and UV-vis spectra [B3LYP/6-31+G(d,p) level of theory] have excellent correlation. Inter-molecular non-covalent interaction of HDO with different gases such as NH3, CO2, CO, H2O is investigated through geometrical counterpoise (gCP) i.e., B3LYP-gCP-D3/6-31G∗ method. Furthermore, the inter-molecular interaction is also supported by geometrical parameters, electronic properties, thermodynamic parameters and charge analysis. All these characterizations have corroborated each other and confirmed the electroactive nature (non-covalent interaction ability) of HDO for the studied gases. Electronic properties such as Ionization Potential (IP), Electron Affinities (EA), electrostatic potential (ESP), density of states (DOS), HOMO, LUMO, and band gap of HDO have been estimated for the first time theoretically.