Spectroscopic investigation, HOMO-LUMO and NLO studies on L-histidinium maleate based on DFT approach

NASA Astrophysics Data System (ADS)

Dhanavel, S.; Stephen, A.; Asirvatham, P. Samuel

2017-05-01

The molecular structure of the title compound L-Histidinium Maleate (LHM) was constructed and optimized based on Density Functional Theory method (DFT-B3LYP) with the 6-31G (d,p) basis set. The fundamental vibrational spectral assignment was analyzed with the aid of optimized structure of LHM. The study on electronic properties such as, HOMO-LUMO energies and absorption wavelength were performed using Time dependent DFT (TD-DFT) approach which reveals that energy transfer occur within the molecule. 13C NMR chemical shift values were measured using Gauge independent atomic orbital method (GIAO) and the obtained values are in good agreement with the reported experimental values. Hardness, ionization potential and electrophilicity index also calculated. The electric dipole moment (μtot) and hyperpolarizability (βtot) values of the investigated molecules were computed. The calculated value (β) was 3.7 times higher than that of urea, which confirms the LHM molecule is a potential candidate for NLO applications.

Investigation of ground state charge transfer complex between paracetamol and p-chloranil through DFT and UV-visible studies

NASA Astrophysics Data System (ADS)

Shukla, Madhulata; Srivastava, Nitin; Saha, Satyen

2012-08-01

The present report deals with the theoretical investigation on ground state structure and charge transfer (CT) transitions in paracetamol (PA)/p-chloranil (CA) complex using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) method. It is found that Cdbnd O bond length of p-chloranil increases on complexation with paracetamol along with considerable amount of charge transfer from PA to CA. TD-DFT calculations have been performed to analyse the observed UV-visible spectrum of PA-CA charge transferred complex. Interestingly, in addition to expected CT transition, a weak symmetry relieved π-π* transition in the chloranil is also observed.

DFT calculations in the assignment of solid-state NMR and crystal structure elucidation of a lanthanum(iii) complex with dithiocarbamate and phenanthroline.

PubMed

Gowda, Vasantha; Laitinen, Risto S; Telkki, Ville-Veikko; Larsson, Anna-Carin; Antzutkin, Oleg N; Lantto, Perttu

2016-12-06

The molecular, crystal, and electronic structures as well as spectroscopic properties of a mononuclear heteroleptic lanthanum(iii) complex with diethyldithiocarbamate and 1,10-phenanthroline ligands (3 : 1) were studied by solid-state 13 C and 15 N cross-polarisation (CP) magic-angle-spinning (MAS) NMR, X-ray diffraction (XRD), and first principles density functional theory (DFT) calculations. A substantially different powder XRD pattern and 13 C and 15 N CP-MAS NMR spectra indicated that the title compound is not isostructural to the previously reported analogous rare earth complexes with the space group P2 1 /n. Both 13 C and 15 N CP-MAS NMR revealed the presence of six structurally different dithiocarbamate groups in the asymmetric unit cell, implying a non-centrosymmetric packing arrangement of molecules. This was supported by single-crystal X-ray crystallography showing that the title compound crystallised in the triclinic space group P1[combining macron]. In addition, the crystal structure also revealed that one of the dithiocarbamate ligands has a conformational disorder. NMR chemical shift calculations employing the periodic gauge including projector augmented wave (GIPAW) approach supported the assignment of the experimental 13 C and 15 N NMR spectra. However, the best correspondences were obtained with the structure where the atomic positions in the X-ray unit cell were optimised at the DFT level. The roles of the scalar and spin-orbit relativistic effects on NMR shielding were investigated using the zeroth-order regular approximation (ZORA) method with the outcome that already the scalar relativistic level qualitatively reproduces the experimental chemical shifts. The electronic properties of the complex were evaluated based on the results of the natural bond orbital (NBO) and topology of the electron density analyses. Overall, we apply a multidisciplinary approach acquiring comprehensive information about the solid-state structure and the metal

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.

Investigations of Topological Surface States in Sb (111) Ultrathin Films by STM/STS Experiments and DFT Calculations

NASA Astrophysics Data System (ADS)

Luo, Ziyu; Yao, Guanggeng; Xu, Wentao; Feng, Yuanping; Wang, Xue-Sen

2014-03-01

Bulk Sb was regarded as a semimetal with a nontrivial topological order. It is worth exploring whether the Sb ultrathin film has the potential to be an elementary topological insulator. In the presence of quantum confinement effect, we investigated the evolution of topological surface states in Sb (111) ultrathin films with different thickness by the scanning tunneling microscopy/ spectroscopy (STM/STS) experiments and density functional theory (DFT) calculations. By comparing the quasiparticle interference (QPI) patterns obtained from Fourier-transform scanning tunneling spectroscopy (FT-STS) and from DFT calculations, we successfully derive the spin properties of topological surface states on Sb (111) ultrathin films. In addition, based on the DFT calculations, the 8BL Sb (111) ultrathin film was proved to possess up to 30% spinseparated topological surface states within the bandgap. Therefore, the highquality 8BL Sb (111) ultrathin film could be regarded as an elementary topological insulator.

Experimental investigation and DFT calculation of different amine/ammonium salts adsorption on kaolinite

NASA Astrophysics Data System (ADS)

Chen, Jun; Min, Fan-fei; Liu, Lingyun; Liu, Chunfu; Lu, Fangqin

2017-10-01

The adsorption of four different amine/ammonium salts of DDA (Dodecyl amine), MDA (N-methyldodecyl amine), DMDA (N,N-dimethyldodecyl amine) and DTAC (Dodecyl trimethyl ammonium chloride) on kaolinite particles was investigated in the study through the measurement of contact angles, zeta potentials, aggregation observation, adsorption and sedimentation. The results show that different amine/ammonium salts can adsorb on the kaolinite surface to enhance the hydrophobicity and reduce the electronegativity of kaolinite particle surface, and thus induce a strong hydrophobic aggregation of kaolinite particles which promotes the settlement of kaolinite. To explore the adsorption mechanism of these four amine/ammonium salts on kaolinite surfaces, the adsorptions of DDA+, MDA+, DMDA+ and DTAC+ on kaolinite (001) surface and (00 1 bar) surface are calculated with DFT (Density functional theory). The DFT calculation results indicate that different amine/ammonium cations can strongly adsorbed on kaolinite (001) surface and (00 1 bar) surface by forming Nsbnd H⋯O strong hydrogen bonds or Csbnd H⋯O weak hydrogen bonds, and there are strongly electrostatic attractions between different amine/ammonium cations and kaolinite surfaces. The main adsorption mechanism of amine/ammonium cations on kaolinite is hydrogen-bond interaction and electrostatic attraction.

Spectroscopic analysis of 8-hydroxyquinoline derivatives and investigation of its reactive properties by DFT and molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Sureshkumar, B.; Mary, Y. Sheena; Resmi, K. S.; Panicker, C. Yohannan; Armaković, Stevan; Armaković, Sanja J.; Van Alsenoy, C.; Narayana, B.; Suma, S.

2018-03-01

Two 8-hydroxyquinoline derivatives, 5,7-dichloro-8-hydroxyquinoline (57DC8HQ) and 5-chloro-7-iodo-8-hydroxy quinoline (5CL7I8HQ) have been investigated in details by means of spectroscopic characterization and computational molecular modelling techniques. FT-IR and FT-Raman experimental spectroscopic approaches have been utilized in order to obtain detailed spectroscopic signatures of title compounds, while DFT calculations have been used in order to visualize and assign vibrations. The computed values of dipole moment, polarizability and hyperpolarizability indicate that the title molecules exhibit NLO properties. The evaluated HOMO and LUMO energies demonstrate the chemical stability of the molecules. NBO analysis is made to study the stability of the molecules arising from hyperconjugative interactions and charge delocalization. DFT calculations have been also used jointly with MD simulations in order to investigate in details global and local reactivity properties of title compounds. Also, molecular docking has been also used in order to investigate affinity of title compounds against decarboxylase inhibitor and quinoline derivatives can be a lead compounds for developing new antiparkinsonian drug.

Semiempirical and DFT Investigations of the Dissociation of Alkyl Halides

ERIC Educational Resources Information Center

Waas, Jack R.

2006-01-01

Enthalpy changes corresponding to the gas phase heats of dissociation of 12 organic halides were calculated using two semiempirical methods, the Hartree-Fock method, and two DFT methods. These calculated values were compared to experimental values where possible. All five methods agreed generally with the expected empirically known trends in the…

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.

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.

DFT based vibrational spectroscopic investigations and biological activity of toxic material monocrotophos

NASA Astrophysics Data System (ADS)

Nimmi, D. E.; Sam, S. P. Chandhini; Praveen, S. G.; Binoy, J.

2018-05-01

Many organophosphate compounds exhibiting toxicity are widely used as pesticides and insecticides whose structural features can be explained excellently using geometric simulation using density functional theory and vibrational spectrum. In this work, the molecular structural parameters and vibrational frequencies of the fundamental modes of Monocrotophoshave been obtained using Density functional theory (DFT), using B3LYP functional with 6-311++G(d, p) basis sets and the detailed vibrational analysis of FT-IR and FT-Ramanspectral bands have been carried out using potential energy distribution (PED). The deviation from the resonance structure of phosphate group due to `bridging of oxygen' and π-resonance of amides has been investigated based on the spectral and geometric data. The molecular docking simulation of Monocrotophos with BSA and DNA has been performed to find the mode of binding and the interactions with BSA has been investigated with UV-Visible spectroscopic method, to assess the strength of binding.

DFT benchmark study for the oxidative addition of CH 4 to Pd. Performance of various density functionals

NASA Astrophysics Data System (ADS)

de Jong, G. Theodoor; Geerke, Daan P.; Diefenbach, Axel; Matthias Bickelhaupt, F.

2005-06-01

We have evaluated the performance of 24 popular density functionals for describing the potential energy surface (PES) of the archetypal oxidative addition reaction of the methane C-H bond to the palladium atom by comparing the results with our recent ab initio [CCSD(T)] benchmark study of this reaction. The density functionals examined cover the local density approximation (LDA), the generalized gradient approximation (GGA), meta-GGAs as well as hybrid density functional theory. Relativistic effects are accounted for through the zeroth-order regular approximation (ZORA). The basis-set dependence of the density-functional-theory (DFT) results is assessed for the Becke-Lee-Yang-Parr (BLYP) functional using a hierarchical series of Slater-type orbital (STO) basis sets ranging from unpolarized double-ζ (DZ) to quadruply polarized quadruple-ζ quality (QZ4P). Stationary points on the reaction surface have been optimized using various GGA functionals, all of which yield geometries that differ only marginally. Counterpoise-corrected relative energies of stationary points are converged to within a few tenths of a kcal/mol if one uses the doubly polarized triple-ζ (TZ2P) basis set and the basis-set superposition error (BSSE) drops to 0.0 kcal/mol for our largest basis set (QZ4P). Best overall agreement with the ab initio benchmark PES is achieved by functionals of the GGA, meta-GGA, and hybrid-DFT type, with mean absolute errors of 1.3-1.4 kcal/mol and errors in activation energies ranging from +0.8 to -1.4 kcal/mol. Interestingly, the well-known BLYP functional compares very reasonably with an only slightly larger mean absolute error of 2.5 kcal/mol and an underestimation by -1.9 kcal/mol of the overall barrier (i.e., the difference in energy between the TS and the separate reactants). For comparison, with B3LYP we arrive at a mean absolute error of 3.8 kcal/mol and an overestimation of the overall barrier by 4.5 kcal/mol.

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.

DFT-based molecular modeling and vibrational study of the La(III) complex of 3,3'-(benzylidene)bis(4-hydroxycoumarin).

PubMed

Mihaylov, Tzvetan; Trendafilova, Natasha; Georgieva, Ivelina

2008-05-01

Molecular modeling of the La(III) complex of 3,3'-(benzylidene)bis(4-hydroxycoumarin) (PhDC) was performed using density functional theory (DFT) methods at B3LYP/6-31G(d) and BP86/TZP levels. Both Stuttgart-Dresden effective core potential and ZORA approximation were applied to the La(III) center. The electron density distribution and the nucleophilic centers of the deprotonated ligand PhDC(2-) in a solvent environment were estimated on the basis of Hirshfeld atomic charges, electrostatic potential values at the nuclei, and Nalewajski-Mrozek bond orders. In accordance with the empirical formula La(PhDC)(OH)(H(2)O), a chain structure of the complex was simulated by means of two types of molecular fragment: (1) two La(III) cations bound to one PhDC(2-) ligand, and (2) two PhDC(2-) ligands bound to one La(III) cation. Different orientations of PhDC(2-), OH(-) and H(2)O ligands in the La(III) complexes were investigated using 20 possible [La(PhDC(2-))(2)(OH)(H(2)O)](2-) fragments. Energy calculations predicted that the prism-like structure based on "tail-head" cis-LML2 type binding and stabilized via HO...HOH intramolecular hydrogen bonds is the most probable structure for the La(III) complex. The calculated vibrational spectrum of the lowest energy La(III) model fragment is in very good agreement with the experimental IR spectrum of the complex, supporting the suggested ligand binding mode to La(III) in a chain structure, namely, every PhDC(2-) interacts with two La(III) cations through both carbonylic and both hydroxylic oxygens, and every La(III) cation binds four oxygen atoms of two different PhDC(2-).

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.

Relativistic DFT investigation of electronic structure effects arising from doping the Au25 nanocluster with transition metals.

PubMed

Alkan, Fahri; Muñoz-Castro, Alvaro; Aikens, Christine M

2017-10-26

We perform a theoretical investigation using density functional theory (DFT) and time-dependent DFT (TDDFT) on the doping of the Au 25 (SR) 18 -1 nanocluster with group IX transition metals (M = cobalt, rhodium and iridium). Different doping motifs, charge states and spin multiplicities were considered for the single-atom doped nanoclusters. Our results show that the interaction (or the lack of interaction) between the d-type energy levels that mainly originate from the dopant atom and the super-atomic levels plays an important role in the energetics, the electronic structure and the optical properties of the doped systems. The evaluated MAu 24 (SR) 18 q (q = -1, -3) systems favor an endohedral disposition of the doping atom typically in a singlet ground state, with either a 6- or 8-valence electron icosahedral core. For the sake of comparison, the role of the d energy levels in the electronic structure of a variety of doped Au 25 (SR) 18 -1 nanoclusters was investigated for dopant atoms from other families such as Cd, Ag and Pd. Finally, the effect of spin-orbit coupling (SOC) on the electronic structure and absorption spectra was determined. The information in this study regarding the relative energetics of the d-based and super-atom energy levels can be useful to extend our understanding of the preferred doping modes of different transition metals in protected gold nanoclusters.

Spectroscopic (FT-IR/FT-Raman) and computational (HF/DFT) investigation and HOMO/LUMO/MEP analysis on 1,1-difluoro-2-vinyl-cyclopropane

NASA Astrophysics Data System (ADS)

Senthil Raj, P.; Shoba, D.; Ramalingam, S.; Periandy, S.

2015-08-01

All the computational calculations were made in the ground state using the HF and DFT (B3LYP) methods with 6-31++G (d,p) and 6-311++G (d,p) basis sets. Making use of the recorded data, the complete vibrational assignments were made and analysis of the observed fundamental bands of molecule was carried out. The shifting of the frequencies in the vibrational pattern of the title molecule due to the substitutions; sbnd CHdbnd CH2 and F were deeply investigated by the vibrational analysis. Moreover, 13C NMR and 1H NMR chemical shifts were calculated by using the gauge independent atomic orbital (GIAO) method with HF/B3LYP methods with 6-311++G (d,p). A study on the electronic properties, such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. Mulliken charges of the 1DF2VCP were also calculated and interpreted. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase.

Acid base chemistry of luteolin and its methyl-ether derivatives: A DFT and ab initio investigation

NASA Astrophysics Data System (ADS)

Amat, Anna; De Angelis, Filippo; Sgamellotti, Antonio; Fantacci, Simona

2008-09-01

The acid-base chemistry of luteolin, a flavonoid with important pharmacological and dyeing properties, and of the related methyl ether derivatives have been investigated by DFT and MP2 methods, testing different computational setups. We calculate the pK's of all the possible deprotonation sites, for which no experimental assignment could be achieved. The calculated pK's deliver a different acidity order for the two most acidic deprotonation sites between luteolin and its methyl ether derivatives, due to intramolecular hydrogen bonding in luteolin. A lowest p Ka of 6.19 is computed for luteolin, in good agreement with available experimental data.

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

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.

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.

Mechanical and magneto-opto-electronic investigation of transition metal based fluoro-perovskites: An ab-initio DFT study

NASA Astrophysics Data System (ADS)

Erum, Nazia; Azhar Iqbal, Muhammad

2017-09-01

Detailed ab-initio calculations are performed to investigate structural, elastic, mechanical, magneto-electronic and optical properties of the KXF3 (X = V, Fe, Co, Ni) fluoro-perovskites using Full Potential Linearized Augmented Plane Wave (FP-LAPW) method within the framework of density functional theory (DFT). The calculated structural parameters by DFT and analytical methods are found consistent with the experimental results. From the elastic and mechanical properties, it can be inferred that these compounds are elastically stable and anisotropic while KCoF3 is harder than rest of the compounds. Furthermore, thermal behavior of these compounds is analyzed by calculating Debye temperature (θD). The calculated spin dependent magneto-electronic properties in these compounds reveal that exchange splitting is dominated by N-3d orbital. The stable magnetic phase optimizations verify the experimental observations at low temperature. Type of chemical bonding is analyzed with the help of variations in electron density difference distribution that is induced due to changes of the second cation. The linear optical properties are also discussed in terms of optical spectra. The present methodology represents an influential approach to calculate the whole set of mechanical and magneto-opto-electronic parameters, which would support to understand various physical phenomena and empower device engineers for implementing these materials in spintronic applications.

Applicability of DFT model in reactive distillation

NASA Astrophysics Data System (ADS)

Staszak, Maciej

2017-11-01

The density functional theory (DFT) applicability to reactive distillation is discussed. Brief modeling techniques description of distillation and rectification with chemical reaction is provided as a background for quantum method usage description. The equilibrium and nonequilibrium distillation models are described for that purpose. The DFT quantum theory is concisely described. The usage of DFT in the modeling of reactive distillation is described in two parts. One of the fundamental and very important component of distillation modeling is vapor-liquid equilibrium description for which the DFT quantum approach can be used. The representative DFT models, namely COSMO-RS (Conductor like Screening Model for Real Solvents), COSMOSPACE (COSMO Surface Pair Activity Coefficient) and COSMO-SAC (SAC - segment activity coefficient) approaches are described. The second part treats the way in which the chemical reaction is described by means of quantum DFT method. The intrinsic reaction coordinate (IRC) method is described which is used to find minimum energy path of substrates to products transition. The DFT is one of the methods which can be used for that purpose. The literature data examples are provided which proves that IRC method is applicable for chemical reaction kinetics description.

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.

Probing the (110)-Oriented plane of rutile ZnF2: A DFT investigation

NASA Astrophysics Data System (ADS)

Tamijani, Ali Abbaspour; Ebrahimiaqda, Elham

2017-12-01

For many years, rutile-like crystals have given rise to pronounced enthusiasm amongst mineralogists. In this context, rutile-type ZnF2 has found numerous applications across a variety of disciplines, ranging from material sciences to optoelectronics. Surprisingly, very limited literature is concerned with the molecular adsorption on ZnF2 surfaces and related energetics. Additionally, surface probing with small particles is a well-entrenched technique to analyze the interfacial properties. In this regard, small organic species are valuable picks. In the present work, we have employed electronic structure calculations to simulate the adsorption of methane, chloroform, pyrrole, benzene, naphthalene, anthracene, tetracene and pentacene at the (110) plane of rutile ZnF2. Dispersion-corrected DFT method was chosen to predict the binding energies and structures of molecule-adsorbed surfaces. Interestingly, a linear proportionality relationship was found between the binding energies of aromatic adsorbates and their respective molecular lengths. By applying this relationship, we were able to predict the adsorption energy of pentacene on ZnF2 to within 2% of our DFT-based result.

DFT Performance Prediction in FFTW

NASA Astrophysics Data System (ADS)

Gu, Liang; Li, Xiaoming

Fastest Fourier Transform in the West (FFTW) is an adaptive FFT library that generates highly efficient Discrete Fourier Transform (DFT) implementations. It is one of the fastest FFT libraries available and it outperforms many adaptive or hand-tuned DFT libraries. Its success largely relies on the huge search space spanned by several FFT algorithms and a set of compiler generated C code (called codelets) for small size DFTs. FFTW empirically finds the best algorithm by measuring the performance of different algorithm combinations. Although the empirical search works very well for FFTW, the search process does not explain why the best plan found performs best, and the search overhead grows polynomially as the DFT size increases. The opposite of empirical search is model-driven optimization. However, it is widely believed that model-driven optimization is inferior to empirical search and is particularly powerless to solve problems as complex as the optimization of DFT.

Nonlinear modeling of crystal system transition of black phosphorus using continuum-DFT model.

PubMed

Setoodeh, A R; Farahmand, H

2018-01-24

In this paper, the nonlinear behavior of black phosphorus crystals is investigated in tandem with dispersion-corrected density functional theory (DFT-D) analysis under uniaxial loadings. From the identified anisotropic behavior of black phosphorus due to its morphological anisotropy, a hyperelastic anisotropic (HA) model named continuum-DFT is established to predict the nonlinear behavior of the material. In this respect, uniaxial Cauchy stresses are employed on both the DFT-D and HA models along the zig-zag and armchair directions. Simultaneously, the transition of the crystal system is recognized at about 4.5 GPa of the applied uniaxial tensile stress along the zig-zag direction on the DFT-D simulation in the nonlinear region. In order to develop the nonlinear continuum model, unknown constants are surveyed with the optimized least square technique. In this regard, the continuum model is obtained to reproduce the Cauchy stress-stretch and density of strain-stretch results of the DFT-D simulation. Consequently, the modified HA model is introduced to characterize the nonlinear behavior of black phosphorus along the zig-zag direction. More importantly, the specific transition of the crystal system is successfully predicted in the new modified continuum-DFT model. The results reveal that the multiscale continuum-DFT model is well defined to replicate the nonlinear behavior of black phosphorus along the zig-zag and armchair directions.

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.

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.

Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) (PHB). An Experimental and DFT Investigation.

PubMed

Clark, Jared M; Pilath, Heidi M; Mittal, Ashutosh; Michener, William E; Robichaud, David J; Johnson, David K

2016-01-28

We demonstrate a synthetic route toward the production of propene directly from poly(β-hydroxybutyrate) (PHB), the most common of a wide range of high-molecular-mass microbial polyhydroxyalkanoates. Propene, a major commercial hydrocarbon, was obtained from the depolymerization of PHB and subsequent decarboxylation of the crotonic acid monomer in good yields (up to 75 mol %). The energetics of PHB depolymerization and the gas-phase decarboxylation of crotonic acid were also studied using density functional theory (DFT). The average activation energy for the cleavage of the R'C(O)O-R linkage is calculated to be 163.9 ± 7.0 kJ mol(-1). Intramolecular, autoacceleration effects regarding the depolymerization of PHB, as suggested in some literature accounts, arising from the formation of crotonyl and carboxyl functional groups in the products could not be confirmed by the results of DFT and microkinetic modeling. DFT results, however, suggest that intermolecular catalysis involving terminal carboxyl groups may accelerate PHB depolymerization. Activation energies for this process were estimated to be about 20 kJ mol(-1) lower than that for the noncatalyzed ester cleavage, 144.3 ± 6.4 kJ mol(-1). DFT calculations predict the decarboxylation of crotonic acid to follow second-order kinetics with an activation energy of 147.5 ± 6.3 kJ mol(-1), consistent with that measured experimentally, 146.9 kJ mol(-1). Microkinetic modeling of the PHB to propene overall reaction predicts decarboxylation of crotonic acid to be the rate-limiting step, consistent with experimental observations. The results also indicate that improvements made to enhance the isomerization of crotonic acid to vinylacetic acid will improve the direct conversion of PHB to propene.

Scalar relativistic computations of nuclear magnetic shielding and g-shifts with the zeroth-order regular approximation and range-separated hybrid density functionals

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

Aquino, Fredy W.; Govind, Niranjan; Autschbach, Jochen

2011-10-01

Density functional theory (DFT) calculations of NMR chemical shifts and molecular g-tensors with Gaussian-type orbitals are implemented via second-order energy derivatives within the scalar relativistic zeroth order regular approximation (ZORA) framework. Nonhybrid functionals, standard (global) hybrids, and range-separated (Coulomb-attenuated, long-range corrected) hybrid functionals are tested. Origin invariance of the results is ensured by use of gauge-including atomic orbital (GIAO) basis functions. The new implementation in the NWChem quantum chemistry package is verified by calculations of nuclear shielding constants for the heavy atoms in HX (X=F, Cl, Br, I, At) and H2X (X = O, S, Se, Te, Po), and Temore » chemical shifts in a number of tellurium compounds. The basis set and functional dependence of g-shifts is investigated for 14 radicals with light and heavy atoms. The problem of accurately predicting F NMR shielding in UF6-nCln, n = 1 to 6, is revisited. The results are sensitive to approximations in the density functionals, indicating a delicate balance of DFT self-interaction vs. correlation. For the uranium halides, the results with the range-separated functionals are mixed.« less

Stereochemical and conformational study on fenoterol by ECD spectroscopy and TD-DFT calculations.

PubMed

Tedesco, Daniele; Zanasi, Riccardo; Wainer, Irving W; Bertucci, Carlo

2014-03-01

Fenoterol and its derivatives are selective β2-adrenergic receptor (β2-AR) agonists whose stereoselective biological activities have been extensively investigated in the past decade; a complete stereochemical characterization of fenoterol derivatives is therefore crucial for a better understanding of the effects of stereochemistry on β2-AR binding. In the present project, the relationship between chiroptical properties and absolute stereochemistry of the stereoisomers of fenoterol (1) was investigated by experimental ECD spectroscopy and time-dependent density functional theory (TD-DFT). DFT geometry optimizations were carried out at the RI-B97D/TZVP/IEFPCM(MeOH) level and subsequent TD-DFT calculations were performed using the PBE0 hybrid functional. Despite the large pool of equilibrium conformers found for the investigated compounds and the known limitations of the level of theory employed, the computational protocol was able to reproduce the experimental ECD spectra of the stereoisomers of 1. The main contribution to the overall chiroptical properties was found to arise from the absolute configuration of the chiral center in α-position to the resorcinol moiety. Based on this evidence, a thorough conformational analysis was performed on the optimized DFT conformers, which revealed the occurrence of a different equilibrium between conformational patterns for the diastereomers of fenoterol: the (R,R')/(S,S') enantiomeric pair showed a higher population of folded conformations than the (R,S')/(S,R') pair. Copyright © 2013 Elsevier B.V. All rights reserved.

Spectroscopic analysis and molecular docking of imidazole derivatives and investigation of its reactive properties by DFT and molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Thomas, Renjith; Hossain, Mossaraf; Mary, Y. Sheena; Resmi, K. S.; Armaković, Stevan; Armaković, Sanja J.; Nanda, Ashis Kumar; Ranjan, Vivek Kumar; Vijayakumar, G.; Van Alsenoy, C.

2018-04-01

Solvent-free synthesis pathway for obtaining two imidazole derivatives (2-chloro-1-(4-methoxyphenyl)-4,5-dimethyl-1H-imidazole (CLMPDI) and 1-(4-bromophenyl)-2-chloro-4,5-dimethyl-1H-imidazole (BPCLDI) has been reported in this work, followed by detailed experimental and computational spectroscopic characterization and reactivity study. Spectroscopic methods encompassed IR, FT-Raman and NMR techniques, with the mutual comparison of experimentally and computationally obtained results at DFT/B3LYP level of theory. Reactivity study based on DFT calculations encompassed molecular orbitals analysis, followed by calculations of molecular electrostatic potential (MEP) and average local ionization energy (ALIE) values, Fukui functions and bond dissociation energies (BDE). Additionally, the stability of title molecules in water has been investigated via molecular dynamics (MD) simulations, while interactivity with aspulvinonedimethylallyl transferase protein has been evaluated by molecular docking procedure. CLMPDI compound showed antimicrobial activity against all four bacterial strain in both gram positive and gram negative bacteria while, BPCLDI showed only in gram positive bacteria, Staphylococcus Aureus (MTCC1144). The first order hyperpolarizability of CLMPDI and BPCLDI are 20.15 and 6.10 times that of the standard NLO material urea.

Adsorption of beryllium atoms and clusters both on graphene and in a bilayer of graphite investigated by DFT.

PubMed

Ferro, Yves; Fernandez, Nicolas; Allouche, Alain; Linsmeier, Christian

2013-01-09

We herein investigate the interaction of beryllium with a graphene sheet and in a bilayer of graphite by means of periodic DFT calculations. In all cases, we find the beryllium atoms to be more weakly bonded on graphene than in the bilayer. Be(2) forms both magnetic and non-magnetic structures on graphene depending on the geometrical configuration of adsorption. We find that the stability of the Be/bilayer system increases with the size of the beryllium clusters inserted into the bilayer of graphite. We also find a charge transfer from beryllium to the graphite layers. All these results are analysed in terms of electronic structure.

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.

Investigation of dissociative electron attachment to 2'-deoxycytidine-3'-monophosphate using DFT method and time dependent wave packet approach

NASA Astrophysics Data System (ADS)

Bhowmick, Somnath; B, Renjith; Mishra, Manoj K.; Sarma, Manabendra

2012-08-01

Effect of electron correlation on single strand breaks (SSBs) induced by low energy electron (LEE) has been investigated in a fragment excised from a DNA, viz., 2'-deoxycytidine-3'-monophosphate [3'-dCMPH] molecule in gas phase at DFT-B3LYP/6-31+G(d) accuracy level and using local complex potential based time dependent wave packet (LCP-TDWP) approach. The results obtained, in conjunction with our earlier investigation, show the possibility of SSB at very low energy (0.15 eV) where the LEE transfers from π* to σ* resonance state which resembles a SN2 type mechanism. In addition, for the first time, an indication of quantum mechanical tunneling in strand breaking is seen from the highest anionic bound vibrational state (χ5), which may have a substantial role during DNA damage.

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.

Robust 3D DFT video watermarking

NASA Astrophysics Data System (ADS)

Deguillaume, Frederic; Csurka, Gabriela; O'Ruanaidh, Joseph J.; Pun, Thierry

1999-04-01

This paper proposes a new approach for digital watermarking and secure copyright protection of videos, the principal aim being to discourage illicit copying and distribution of copyrighted material. The method presented here is based on the discrete Fourier transform (DFT) of three dimensional chunks of video scene, in contrast with previous works on video watermarking where each video frame was marked separately, or where only intra-frame or motion compensation parameters were marked in MPEG compressed videos. Two kinds of information are hidden in the video: a watermark and a template. Both are encoded using an owner key to ensure the system security and are embedded in the 3D DFT magnitude of video chunks. The watermark is a copyright information encoded in the form of a spread spectrum signal. The template is a key based grid and is used to detect and invert the effect of frame-rate changes, aspect-ratio modification and rescaling of frames. The template search and matching is performed in the log-log-log map of the 3D DFT magnitude. The performance of the presented technique is evaluated experimentally and compared with a frame-by-frame 2D DFT watermarking approach.

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.

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.

Vibrational spectroscopic and structural investigations on fullerene: A DFT approach

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

Christy, P. Anto; Premkumar, S.; Asath, R. Mohamed

2016-05-06

The molecular structure of fullerene (C{sub 60}) molecule was optimized by the DFT/B3LYP method with 6-31G and 6-31G(d,p) basis sets using Gaussian 09 program. The vibrational frequencies were calculated for the optimized molecular structure of the molecule. The calculated vibrational frequencies confirm that the molecular structure of the molecule was located at the minimum energy potential energy surface. The calculated vibrational frequencies were assigned on the basis of functional group analysis and also confirmed using the GaussView 05 software. The frontier molecular orbitals analysis was carried out. The FMOs related molecular properties were predicted. The higher ionization potential, higher electronmore » affinity, higher softness, lower band gap energy and lower hardness values were obtained, which confirm that the fullerene molecule has a higher molecular reactivity. The Mulliken atomic charge distribution of the molecule was also calculated. Hence, these results play an important role due to its potential applications as drug delivery devices.« less

Assessment of TD-DFT and LF-DFT for study of d − d transitions in first row transition metal hexaaqua complexes

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

Vlahović, Filip; Perić, Marko; Zlatar, Matija, E-mail: matijaz@chem.bg.ac.rs

2015-06-07

Herein, we present the systematic, comparative computational study of the d − d transitions in a series of first row transition metal hexaaqua complexes, [M(H{sub 2}O){sub 6}]{sup n+} (M{sup 2+/3+} = V {sup 2+/3+}, Cr{sup 2+/3+}, Mn{sup 2+/3+}, Fe{sup 2+/3+}, Co{sup 2+/3+}, Ni{sup 2+}) by the means of Time-dependent Density Functional Theory (TD-DFT) and Ligand Field Density Functional Theory (LF-DFT). Influence of various exchange-correlation (XC) approximations have been studied, and results have been compared to the experimental transition energies, as well as, to the previous high-level ab initio calculations. TD-DFT gives satisfactory results in the cases of d{sup 2}, d{supmore » 4}, and low-spin d{sup 6} complexes, but fails in the cases when transitions depend only on the ligand field splitting, and for states with strong character of double excitation. LF-DFT, as a non-empirical approach to the ligand field theory, takes into account in a balanced way both dynamic and non-dynamic correlation effects and hence accurately describes the multiplets of transition metal complexes, even in difficult cases such as sextet-quartet splitting in d{sup 5} complexes. Use of the XC functionals designed for the accurate description of the spin-state splitting, e.g., OPBE, OPBE0, or SSB-D, is found to be crucial for proper prediction of the spin-forbidden excitations by LF-DFT. It is shown that LF-DFT is a valuable alternative to both TD-DFT and ab initio methods.« less

Time-dependent i-DFT exchange-correlation potentials with memory: applications to the out-of-equilibrium Anderson model

NASA Astrophysics Data System (ADS)

Kurth, Stefan; Stefanucci, Gianluca

2018-06-01

We have recently put forward a steady-state density functional theory (i-DFT) to calculate the transport coefficients of quantum junctions. Within i-DFT it is possible to obtain the steady density on and the steady current through an interacting junction using a fictitious noninteracting junction subject to an effective gate and bias potential. In this work we extend i-DFT to the time domain for the single-impurity Anderson model. By a reverse engineering procedure we extract the exchange-correlation (xc) potential and xc bias at temperatures above the Kondo temperature T K. The derivation is based on a generalization of a recent paper by Dittmann et al. [N. Dittmann et al., Phys. Rev. Lett. 120, 157701 (2018)]. Interestingly the time-dependent (TD) i-DFT potentials depend on the system's history only through the first time-derivative of the density. We perform numerical simulations of the early transient current and investigate the role of the history dependence. We also empirically extend the history-dependent TD i-DFT potentials to temperatures below T K. For this purpose we use a recently proposed parametrization of the i-DFT potentials which yields highly accurate results in the steady state.

OH-initiated transformation and hydrolysis of aspirin in AOPs system: DFT and experimental studies.

PubMed

He, Lin; Sun, Xiaomin; Zhu, Fanping; Ren, Shaojie; Wang, Shuguang

2017-08-15

Advanced oxidation processes (AOPs) are widely used in wastewater treatment of pharmaceutical and personal care products (PPCPs). In this work, the OH-initiated transformation as well as the hydrolysis of a typical PPCPs, aspirin, was investigated using density functional theory (DFT) calculations and laboratory experiments. For DFT calculations, the frontier electron densities and bond dissociation energies were analyzed. Profiles of the potential energy surface were constructed, and all the possible pathways were discussed. Additionally, rate constants for each pathway were calculated with transition state theory (TST) method. UV/H 2 O 2 experiments of aspirin were performed and degradation intermediates were identified by UPLC-MS-MS analysis. Different findings from previous experimental works were reported that the H-abstraction pathways at methyl position were dominated and OH-addition pathways on benzene ring were also favored. Meantime, hydroxyl ASA was confirmed as the main stable intermediate. Moreover, it was the first time to use DFT method to investigate the hydrolysis mechanisms of organic ester compound. Copyright © 2017 Elsevier B.V. All rights reserved.

The spectroscopic properties of anticancer drug Apigenin investigated by using DFT calculations, FT-IR, FT-Raman and NMR analysis

NASA Astrophysics Data System (ADS)

Mariappan, G.; Sundaraganesan, N.; Manoharan, S.

2012-09-01

The FT-Raman and FT-Infrared spectra of solid Apigenin sample were measured in order to elucidate the spectroscopic properties of title molecule in the spectral range of 3500-50 cm-1 and 4000-400 cm-1, respectively. The recorded FT-IR and FT-Raman spectral measurements favor the calculated (by B3LYP/6-31G(d,p) method) structural parameters which are further supported by spectral simulation. Additional support is given by the collected 1H and 13C NMR spectra recorded with the sample dissolved in DMSO. The predicted chemical shifts at the B3LYP/6-31G(d) level obtained using the Gauge-Invariant Atomic Orbitals (GIAO) method with and without inclusion of solvent using the Polarizable Continuum Model (PCM). By using TD-DFT method, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental one is determined. The UV-visible absorption spectra of the compound that dissolved in Ethanol, Methanol and DMSO were recorded in the range of 800-200 nm. The formation of hydrogen bond and the most possible interaction are explained using natural bond orbital (NBO) analysis. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis and atomic charges of the title compound were investigated using theoretical calculations. The results are discussed herein and compared with similar molecules whenever appropriate.

Complexation of rhodium(II) tetracarboxylates with aliphatic diamines in solution: 1H and 13C NMR and DFT investigations.

PubMed

Jaźwiński, Jarosław; Sadlej, Agnieszka

2013-10-01

The complexation of rhodium(II) tetraacetate, tetrakistrifluoroaceate and tetrakisoctanoate with a set of diamines (ethane-1,diamine, propane-1,3-diamine and nonane-1,9-diamine) and their N,N'-dimethyl and N,N,N',N'-tetramethyl derivatives in chloroform solution has been investigated by (1) H and (13) C NMR spectroscopy and density functional theory (DFT) modelling. A combination of two bifunctional reagents, diamines and rhodium(II) tetracarboxylates, yielded insoluble coordination polymers as main products of complexation and various adducts in the solution, being in equilibrium with insoluble material. All diamines initially formed the 2 : 1 (blue), (1 : 1)n oligomeric (red) and 1 : 2 (red) axial adducts in solution, depending on the reagents' molar ratio. Adducts of primary and secondary diamines decomposed in the presence of ligand excess, the former via unstable equatorial complexes. The complexation of secondary diamines slowed down the inversion at nitrogen atoms in NH(CH3 ) functional groups and resulted in the formation of nitrogenous stereogenic centres, detectable by NMR. Axial adducts of tertiary diamines appeared to be relatively stable. The presence of long aliphatic chains in molecules (adducts of nonane-1,9-diamines or rhodium(II) tetrakisoctanoate) increased adduct solubility. Hypothetical structures of the equatorial adduct of rhodium(II) tetraacetate with ethane-1,2-diamine and their NMR parameters were explored by means of DFT calculations. Copyright © 2013 John Wiley & Sons, Ltd.

Comparison of discrete Fourier transform (DFT) and principal component analysis/DFT as forecasting tools for absorbance time series received by UV-visible probes installed in urban sewer systems.

PubMed

Plazas-Nossa, Leonardo; Torres, Andrés

2014-01-01

The objective of this work is to introduce a forecasting method for UV-Vis spectrometry time series that combines principal component analysis (PCA) and discrete Fourier transform (DFT), and to compare the results obtained with those obtained by using DFT. Three time series for three different study sites were used: (i) Salitre wastewater treatment plant (WWTP) in Bogotá; (ii) Gibraltar pumping station in Bogotá; and (iii) San Fernando WWTP in Itagüí (in the south part of Medellín). Each of these time series had an equal number of samples (1051). In general terms, the results obtained are hardly generalizable, as they seem to be highly dependent on specific water system dynamics; however, some trends can be outlined: (i) for UV range, DFT and PCA/DFT forecasting accuracy were almost the same; (ii) for visible range, the PCA/DFT forecasting procedure proposed gives systematically lower forecasting errors and variability than those obtained with the DFT procedure; and (iii) for short forecasting times the PCA/DFT procedure proposed is more suitable than the DFT procedure, according to processing times obtained.

Numerical Nuclear Second Derivatives on a Computing Grid: Enabling and Accelerating Frequency Calculations on Complex Molecular Systems.

PubMed

Yang, Tzuhsiung; Berry, John F

2018-06-04

The computation of nuclear second derivatives of energy, or the nuclear Hessian, is an essential routine in quantum chemical investigations of ground and transition states, thermodynamic calculations, and molecular vibrations. Analytic nuclear Hessian computations require the resolution of costly coupled-perturbed self-consistent field (CP-SCF) equations, while numerical differentiation of analytic first derivatives has an unfavorable 6 N ( N = number of atoms) prefactor. Herein, we present a new method in which grid computing is used to accelerate and/or enable the evaluation of the nuclear Hessian via numerical differentiation: NUMFREQ@Grid. Nuclear Hessians were successfully evaluated by NUMFREQ@Grid at the DFT level as well as using RIJCOSX-ZORA-MP2 or RIJCOSX-ZORA-B2PLYP for a set of linear polyacenes with systematically increasing size. For the larger members of this group, NUMFREQ@Grid was found to outperform the wall clock time of analytic Hessian evaluation; at the MP2 or B2LYP levels, these Hessians cannot even be evaluated analytically. We also evaluated a 156-atom catalytically relevant open-shell transition metal complex and found that NUMFREQ@Grid is faster (7.7 times shorter wall clock time) and less demanding (4.4 times less memory requirement) than an analytic Hessian. Capitalizing on the capabilities of parallel grid computing, NUMFREQ@Grid can outperform analytic methods in terms of wall time, memory requirements, and treatable system size. The NUMFREQ@Grid method presented herein demonstrates how grid computing can be used to facilitate embarrassingly parallel computational procedures and is a pioneer for future implementations.

Using DFT Methods to Study Activators in Optical Materials

DOE PAGES

Du, Mao-Hua

2015-08-17

Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns 2 ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, and can be used to search for newmore » materials. DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn 4+ activated red phosphors, scintillators activated by Ce 3+, Eu 2+, Tl +, and excitons are shown as examples of using DFT calculations in phosphor and scintillator research.« less

A DFT Investigation of the Mechanism of Propene Ammoxidation over α-Bismuth Molybdate

DOE PAGES

Licht, Rachel B.; Bell, Alexis T.

2016-11-17

We investigated the mechanisms and energetics for the propene oxidation and ammoxidation occurring on the (010) surface of Bi 2 Mo 3 O 12 using density functional theory (DFT). An energetically feasible sequence of elementary steps for propene oxidation to acrolein, propene ammoxidation to acrylonitrile, and acrolein ammoxidation to acrylonitrile is proposed. Consistent with experimental findings, the rate-limiting step for both propene oxidation and ammoxidation is the initial hydrogen abstraction from the methyl group of propene, which is calculated to have an apparent activation energy of 27.3 kcal/mol. The allyl species produced in this reaction is stabilized as an allylmore » alkoxide, which can then undergo hydrogen abstraction to form acrolein or react with ammonia adsorbed on under-coordinated surface Bi 3+ cations to form allylamine. Dehydrogenation of allylamine is shown to produce acrylonitrile, whereas reaction with additional adsorbed ammonia leads to the formation of acetonitrile and hydrogen cyanide. The dehydrogenation of allyalkoxide species is found to have a significantly higher activation barrier than reaction with adsorbed ammonia, consistent with the observation that very little acrolein is produced when ammonia is present. Finally, we found that rapid reoxidation of the catalyst surface to release wate the driving force for all reactions involving the cleavage of C-H or N-H bonds, because practically all of these steps are endothermic. (Chemical Equation Presented).« less

A DFT investigation on interactions between asymmetric derivatives of cisplatin and nucleobase guanine

NASA Astrophysics Data System (ADS)

Tai, Truong Ba; Nhat, Pham Vu

2017-07-01

The interactions of hydrolysis products of cisplatin and its asymmetric derivatives cis- and trans-[PtCl2(iPram)(Mepz)] with guanine were studied using DFT methods. These interactions are dominated by electrostatic effects, namely hydrogen bond contributions and there exists a charge flow from H-atoms of ligands to the O-atoms of guanine. The replacement of NH3 moieties by larger functional groups accompanies with a moderate reaction between PtII and guanine molecule, diminishing the cytotoxicity of the drug. The asymmetric and symmetric NH2 stretching modes of complexes having strong hydrogen bond interactions are red shifted importantly as compared to complexes without presence of hydrogen bond interactions.

Synthesis, crystal structure investigation, spectroscopic characterizations and DFT computations on a novel 1-(2-chloro-4-phenylquinolin-3-yl)ethanone

NASA Astrophysics Data System (ADS)

Murugavel, S.; Stephen, C. S. Jacob Prasanna; Subashini, R.; Reddy, H. Raveendranatha; AnanthaKrishnan, Dhanabalan

2016-10-01

The title compound 1-(2-chloro-4-phenylquinolin-3-yl)ethanone (CPQE) was synthesised effectively by chlorination of 3-acetyl-4-phenylquinolin-2(1H)-one (APQ) using POCl3 reagent. Structural and vibrational spectroscopic studies were performed by utilizing single crystal X-ray diffraction, FTIR and NMR spectral analysis along with DFT method utilizing GAUSSIAN‧ 03 software. Veda program has been employed to perform a detailed interpretation of vibrational spectra. Mulliken population analyses on atomic charges, MEP, HOMO-LUMO, NBO, Global chemical reactivity descriptors and thermodynamic properties have been examined by (DFT/B3LYP) method with the 6-311G(d,p) basis set level.

Optical characterization of shock-induced chemistry in the explosive nitromethane using DFT and time-dependent DFT

NASA Astrophysics Data System (ADS)

Pellouchoud, Lenson; Reed, Evan

2014-03-01

With continual improvements in ultrafast optical spectroscopy and new multi-scale methods for simulating chemistry for hundreds of picoseconds, the opportunity is beginning to exist to connect experiments with simulations on the same timescale. We compute the optical properties of the liquid phase energetic material nitromethane (CH3NO2) for the first 100 picoseconds behind the front of a simulated shock at 6.5km/s, close to the experimentally observed detonation shock speed. We utilize molecular dynamics trajectories computed using the multi-scale shock technique (MSST) for time-resolved optical spectrum calculations based on both linear response time-dependent DFT (TDDFT) and the Kubo-Greenwood (KG) formula within Kohn-Sham DFT. We find that TDDFT predicts optical conductivities 25-35% lower than KG-based values and provides better agreement with the experimentally measured index of refraction of unreacted nitromethane. We investigate the influence of electronic temperature on the KG spectra and find no significant effect at optical wavelengths. With all methods, the spectra evolve non-monotonically in time as shock-induced chemistry takes place. We attribute the time-resolved absorption at optical wavelengths to time-dependent populations of molecular decomposition products, including NO, CNO, CNOH, H2O, and larger molecules. Supported by NASA Space Technology Research Fellowship (NSTRF) #NNX12AM48H.

DFT and TD-DFT computation of charge transfer complex between o-phenylenediamine and 3,5-dinitrosalicylic acid

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

Afroz, Ziya; Zulkarnain,; Ahmad, Afaq, E-mail: afaqahmad3@gmail.com

2016-05-23

DFT and TD-DFT studies of o-phenylenediamine (PDA), 3,5-dinitrosalicylic acid (DNSA) and their charge transfer complex have been carried out at B3LYP/6-311G(d,p) level of theory. Molecular geometry and various other molecular properties like natural atomic charges, ionization potential, electron affinity, band gap, natural bond orbital (NBO) and frontier molecular analysis have been presented at same level of theory. Frontier molecular orbital and natural bond orbital analysis show the charge delocalization from PDA to DNSA.

Spectroscopic investigation on structure (monomer and dimer), molecular characteristics and comparative study on vibrational analysis of picolinic and isonicotinic acids using experimental and theoretical (DFT & IVP) methods

NASA Astrophysics Data System (ADS)

Ramesh, Gaddam; Reddy, Byru Venkatram

2018-05-01

In this investigation, the monomeric structure is determined for picolinic and isonicotinic acids based on geometry optimization for one of the four possible conformers and intramolecular hydrogen bond of Osbnd H⋯O using density functional theory (DFT) employing B3LYP functional supplemented with 6-311++G(d,p) basis set. Using this optimized monomeric form, the dimer structure is determined based on minimum energy and length of hydrogen bonds obtained for two possible dimeric forms yielded due to head-to-tail intermolecular Osbnd H⋯N hydrogen bond (dimer 1) linkage and tail-to -tail intermolecular Osbnd H⋯O hydrogen bond (dimer 2) linkage between pyridine ring and carboxyl group. The structure parameters obtained for monomer and dimer forms are in good agreement with the experimental literature values. The vibrational assignments have been made unambiguously for all the vibrations from FTIR and FT-Raman spectra based on the potential energy distribution (PED) and eigen vectors obtained in DFT and inverse vibrational problem (IVP) computations. The rms error between the observed and scaled frequencies is 7.7 and 9.4 cm-1 for PIA and INA, respectively. A 74-element modified valence force field is derived by Wilson's GF matrix method using 58 experimental frequencies of the two molecules in overlay least-squares technique. The average error between observed and computed frequencies by this method is calculated to be 10.39 cm-1. The results of both DFT and IVP computations yielded good agreement between observed and calculated frequencies. The NLO behaviour using hyperpolarizability values; and HOMO and LUMO energies; of the two molecules are investigated by DFT. Charge density distribution and site of chemical reactivity of the molecules are studied by molecular electrostatic surface potential (MESP). Stability of the molecules arising from hyper conjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO

Synthesis and spectroscopical study of rhodanine derivative using DFT approaches

NASA Astrophysics Data System (ADS)

Anbarasan, R.; Dhandapani, A.; Manivarman, S.; Subashchandrabose, S.; Saleem, H.

2015-07-01

The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of (E)-5-benzylidene-2-thioxothiazolidine-4-one (E5BTTO) have been investigated experimentally and theoretically based on Density Functional Theory (DFT) approach. The FT-Raman and FT-IR spectra of E5BTTO were recorded in solid phase. Theoretical calculations were performed at the DFT level using the Gaussian 03 program. The experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumber by their Total Energy Distribution (TED). The results of the calculation were applied to simulate infrared and raman spectra of the title compound which showed good agreement with the observed spectra. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Stability arising from hyperconjugative interactions leading to its NLO activity and charge delocalization were analyzed using Natural Bond Orbital (NBO) analysis.

Structural investigation of (2E)-2-(ethoxycarbonyl)-3-[(4-methoxyphenyl)amino]prop-2-enoic acid: X-ray crystal structure, spectroscopy and DFT

NASA Astrophysics Data System (ADS)

Venkatesan, Perumal; Rajakannan, Venkatachalam; Venkataramanan, Natarajan S.; Ilangovan, Andivelu; Sundius, Tom; Thamotharan, Subbiah

2016-09-01

The title compound, (2E)-2-(ethoxycarbonyl)-3-[(4-methoxyphenyl)amino]prop-2-enoic acid is characterized by means of X-ray crystallography, spectroscopic methods and quantum chemical calculations. The title compound crystallizes in centrosymmetric space group P21/c. Moreover, the crystal structure is primarily stabilized through intramolecular Nsbnd H⋯O and Osbnd H⋯O and intermolecular Nsbnd H⋯O and Csbnd H⋯O interactions along with carbonyl⋯carbonyl and Csbnd H⋯C contacts. These intermolecular interactions are analysed and quantified by using Hirshfeld surface analysis, PIXEL energy, NBO, AIM and DFT calculations. The overall lattice energies of the title and parent compounds suggest that the title compound is stabilized by a 4.5 kcal mol-1 higher energy than the parent compound. The additional stabilization force comes from the methoxy substitution on the title molecule, which is evident since the methoxy group is involved in the intermolecular Csbnd H⋯O interaction as an acceptor. The vibrational modes of the interacting groups are investigated using both experimental and theoretical FT-IR and FT-Raman spectra. The experimental and theoretical UV-Vis spectra agree well. The time dependent DFT spectra show that the ligand-to-ligand charge transfer is responsible for the intense absorbance of the compound.

A DFT and structural investigation of the conformations of Fischer carbene complexes

NASA Astrophysics Data System (ADS)

Landman, Marilé

2015-09-01

A set of different Fischer carbene complexes of group VI and VII metals, with varied heteroatom and heteroaromatic substituents on the carbene carbon atom, was studied. Density functional theory as well as single crystal diffraction techniques were employed to investigated the most stable conformation of these complexes. The complexes studied, [M(CO)4L{C(X)Z}], with L = PPh3 or CO, X = ethoxy (-OCH2CH3) or amino (-NH2 or NHCy) substituents as the heteroatom carbene substituents, Z = 2-furyl (-C4H3O), 2-thienyl (-C4H3S), 2-(N-methyl)pyrrolyl (-C4H3NCH3) as the second carbene substituent had their substituents varied systematically to give all the possible conformations of these complexes. The conformations of the complexes, in particular the relative orientations of the heteroatoms in the molecule (syn vs. anti), E/Z isomerism in the aminocarbene complexes and cis/trans isomerism in the ligand substituted complexes as well as various combinations of these aspects, were studied. In general, it was found that the most stable conformation theoretically as well as in the solid state for most of the complexes preferred the syn conformation. The Z-isomer is generally preferred over the E isomer while the cis is more predominant than the trans isomer. Using DFT and NBO calculations, explanations for the preferred conformations were explored. It was concluded that both steric and electronic factors influence the conformations of the carbene complexes, with the extent of contribution of these two factors varying for each of the different carbene substituents.

Plane-Wave DFT Methods for Chemistry

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

Bylaska, Eric J.

A detailed description of modern plane-wave DFT methods and software (contained in the NWChem package) are described that allow for both geometry optimization and ab initio molecular dynamics simulations. Significant emphasis is placed on aspects of these methods that are of interest to computational chemists and useful for simulating chemistry, including techniques for calculating charged systems, exact exchange (i.e. hybrid DFT methods), and highly efficient AIMD/MM methods. Sample applications on the structure of the goethite+water interface and the hydrolysis of nitroaromatic molecules are described.

NMR shielding calculations across the periodic table: diamagnetic uranium compounds. 2. Ligand and metal NMR.

PubMed

Schreckenbach, Georg

2002-12-16

In this and a previous article (J. Phys. Chem. A 2000, 104, 8244), the range of application for relativistic density functional theory (DFT) is extended to the calculation of nuclear magnetic resonance (NMR) shieldings and chemical shifts in diamagnetic actinide compounds. Two relativistic DFT methods are used, ZORA ("zeroth-order regular approximation") and the quasirelativistic (QR) method. In the given second paper, NMR shieldings and chemical shifts are calculated and discussed for a wide range of compounds. The molecules studied comprise uranyl complexes, [UO(2)L(n)](+/-)(q); UF(6); inorganic UF(6) derivatives, UF(6-n)Cl(n), n = 0-6; and organometallic UF(6) derivatives, UF(6-n)(OCH(3))(n), n = 0-5. Uranyl complexes include [UO(2)F(4)](2-), [UO(2)Cl(4)](2-), [UO(2)(OH)(4)](2-), [UO(2)(CO(3))(3)](4-), and [UO(2)(H(2)O)(5)](2+). For the ligand NMR, moderate (e.g., (19)F NMR chemical shifts in UF(6-n)Cl(n)) to excellent agreement [e.g., (19)F chemical shift tensor in UF(6) or (1)H NMR in UF(6-n)(OCH(3))(n)] has been found between theory and experiment. The methods have been used to calculate the experimentally unknown (235)U NMR chemical shifts. A large chemical shift range of at least 21,000 ppm has been predicted for the (235)U nucleus. ZORA spin-orbit appears to be the most accurate method for predicting actinide metal chemical shifts. Trends in the (235)U NMR chemical shifts of UF(6-n)L(n) molecules are analyzed and explained in terms of the calculated electronic structure. It is argued that the energy separation and interaction between occupied and virtual orbitals with f-character are the determining factors.

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

Predicting the properties of the lead alloys from DFT calculations

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

Buimaga-Iarinca, L., E-mail: luiza.iarinca@itim-cj.ro; Calborean, A.

2015-12-23

We provide qualitative results for the physical properties of the lead alloys at atomic scale by using DFT calculations. Our approach is based on the two assumptions: (i) the geometric structure of lead atoms provides a matrix where the alloying elements can take their positions in the structure as substitutions and (ii) there is a small probability of a direct interaction between the alloying elements, thus the interactions of each alloying element may be approximated by the interactions to the lead matrix. DFT calculations are used to investigate the interaction between several types of impurities and the lead matrix formore » low concentrations of the alloying element. We report results such as the enthalpy of formation, charge transfer and mechanical stress induced by the impurities in the lead matrix; these results can be used as qualitative guide in tuning the physico-chemical properties of the lead alloys.« less

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.

DFT-GGA errors in NO chemisorption energies on (111) transition metal surfaces

NASA Astrophysics Data System (ADS)

Huang, Xu; Mason, Sara E.

2014-03-01

We investigate whether well-known DFT-GGA errors in predicting the chemisorption energy (Echem) of CO on transition metal surfaces manifest in analogous NO chemisorption systems. While widely investigated in the case of CO/metal, analogous DFT-GGA errors have long been claimed to be absent in NO/metal chemisorption. Here, we provide theoretical evidence of systematic enhanced back-donation in NO/metal chemisorption at the DFT-GGA level. We use electronic structure analysis to show that the partially filled molecular NO 2π* orbital rehybridizes with the transition metal d-band to form new bonding and anti-bonding states. We relate the back-donation charge transfer associated with chemisorption to the promotion of an electron from the 5σ orbital to the 2π* orbital in the gas-phase NO G2Σ- ← X2Π excitation. We establish linear relationships between Echem and ΔEG ← X and formulate an Echem correction scheme in the style of Mason et al. [Physical Review B 69, 161401(R)]. We apply the NO Echem correction method to the (111) surfaces of Pt, Pd, Rh, and Ir, with NO chemisorption modeled at a coverage of 0.25 ML. We note that the slope of Echemvs. ΔEG ← X and the dipole moment depend strongly on adsorption site for each metal, and we construct an approximate correction scheme which we test using NO/Pt(100) chemisorption.

Electromechanical and Chemical Sensing at the Nanoscale: DFT and Transport Modeling

NASA Astrophysics Data System (ADS)

Maiti, Amitesh

Of the many nanoelectronic applications proposed for near to medium-term commercial deployment, sensors based on carbon nanotubes (CNT) and metal-oxide nanowires are receiving significant attention from researchers. Such devices typically operate on the basis of the changes of electrical response characteristics of the active component (CNT or nanowire) when subjected to an externally applied mechanical stress or the adsorption of a chemical or bio-molecule. Practical development of such technologies can greatly benefit from quantum chemical modeling based on density functional theory (DFT), and from electronic transport modeling based on non-equilibrium Green's function (NEGF). DFT can compute useful quantities like possible bond-rearrangements, binding energy, charge transfer, and changes to the electronic structure, while NEGF can predict changes in electronic transport behavior and contact resistance. Effects of surrounding medium and intrinsic structural defects can also be taken into account. In this work we review some recent DFT and transport investigations on (1) CNT-based nano-electromechanical sensors (NEMS) and (2) gas-sensing properties of CNTs and metal-oxide nanowires. We also briefly discuss our current understanding of CNT-metal contacts which, depending upon the metal, the deposition technique, and the masking method can have a significant effect on device performance.

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.

A gauge-independent zeroth-order regular approximation to the exact relativistic Hamiltonian—Formulation and applications

NASA Astrophysics Data System (ADS)

Filatov, Michael; Cremer, Dieter

2005-01-01

A simple modification of the zeroth-order regular approximation (ZORA) in relativistic theory is suggested to suppress its erroneous gauge dependence to a high level of approximation. The method, coined gauge-independent ZORA (ZORA-GI), can be easily installed in any existing nonrelativistic quantum chemical package by programming simple one-electron matrix elements for the quasirelativistic Hamiltonian. Results of benchmark calculations obtained with ZORA-GI at the Hartree-Fock (HF) and second-order Møller-Plesset perturbation theory (MP2) level for dihalogens X2 (X=F,Cl,Br,I,At) are in good agreement with the results of four-component relativistic calculations (HF level) and experimental data (MP2 level). ZORA-GI calculations based on MP2 or coupled-cluster theory with single and double perturbations and a perturbative inclusion of triple excitations [CCSD(T)] lead to accurate atomization energies and molecular geometries for the tetroxides of group VIII elements. With ZORA-GI/CCSD(T), an improved estimate for the atomization energy of hassium (Z=108) tetroxide is obtained.

Understanding density functional theory (DFT) and completing it in practice

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

Bagayoko, Diola

2014-12-15

We review some salient points in the derivation of density functional theory (DFT) and of the local density approximation (LDA) of it. We then articulate an understanding of DFT and LDA that seems to be ignored in the literature. We note the well-established failures of many DFT and LDA calculations to reproduce the measured energy gaps of finite systems and band gaps of semiconductors and insulators. We then illustrate significant differences between the results from self consistent calculations using single trial basis sets and those from computations following the Bagayoko, Zhao, and Williams (BZW) method, as enhanced by Ekuma andmore » Franklin (BZW-EF). Unlike the former, the latter calculations verifiably attain the absolute minima of the occupied energies, as required by DFT. These minima are one of the reasons for the agreement between their results and corresponding, experimental ones for the band gap and a host of other properties. Further, we note predictions of DFT BZW-EF calculations that have been confirmed by experiment. Our subsequent description of the BZW-EF method ends with the application of the Rayleigh theorem in the selection, among the several calculations the method requires, of the one whose results have a full, physics content ascribed to DFT. This application of the Rayleigh theorem adds to or completes DFT, in practice, to preserve the physical content of unoccupied, low energy levels. Discussions, including implications of the method, and a short conclusion follow the description of the method. The successive augmentation of the basis set in the BZW-EF method, needed for the application of the Rayleigh theorem, is also necessary in the search for the absolute minima of the occupied energies, in practice.« less

Charge transfer complex between 2,3-diaminopyridine with chloranilic acid. Synthesis, characterization and DFT, TD-DFT computational studies

NASA Astrophysics Data System (ADS)

Al-Ahmary, Khairia M.; Habeeb, Moustafa M.; Al-Obidan, Areej H.

2018-05-01

New charge transfer complex (CTC) between the electron donor 2,3-diaminopyridine (DAP) with the electron acceptor chloranilic (CLA) acid has been synthesized and characterized experimentally and theoretically using a variety of physicochemical techniques. The experimental work included the use of elemental analysis, UV-vis, IR and 1H NMR studies to characterize the complex. Electronic spectra have been carried out in different hydrogen bonded solvents, methanol (MeOH), acetonitrile (AN) and 1:1 mixture from AN-MeOH. The molecular composition of the complex was identified to be 1:1 from Jobs and molar ratio methods. The stability constant was determined using minimum-maximum absorbances method where it recorded high values confirming the high stability of the formed complex. The solid complex was prepared and characterized by elemental analysis that confirmed its formation in 1:1 stoichiometric ratio. Both IR and NMR studies asserted the existence of proton and charge transfers in the formed complex. For supporting the experimental results, DFT computations were carried out using B3LYP/6-31G(d,p) method to compute the optimized structures of the reactants and complex, their geometrical parameters, reactivity parameters, molecular electrostatic potential map and frontier molecular orbitals. The analysis of DFT results strongly confirmed the high stability of the formed complex based on existing charge transfer beside proton transfer hydrogen bonding concordant with experimental results. The origin of electronic spectra was analyzed using TD-DFT method where the observed λmax are strongly consisted with the computed ones. TD-DFT showed the contributed states for various electronic transitions.

Paramagnetic species on catalytic surfaces--DFT investigations into structure sensitivity of the hyperfine coupling constants.

PubMed

Sojka, Zbigniew; Pietrzyk, Piotr

2004-05-01

Structure sensitivity of the hyperfine coupling constants was investigated by means of DFT calculations for selected surface paramagnetic species. A *CH2OH radical trapped on silica and intrazeolite copper nitrosyl adducts encaged in ZSM-5 were taken as the examples. The surface of amorphous silica was modeled with a [Si5O8H10] cluster, whereas the zeolite hosting sites were epitomized by [Si4AlO5(OH)10]- cluster. Three different coordination modes of the *CH2OH radical were considered and the isotropic 13C and 1H hyperfine constants of the resultant van der Waals complexes, calculated with B3LYP/6-311G(d), were discussed in terms of the angular deformations caused by hydrogen bonds with the cluster. The magnetic parameters of the eta1-N[CuNO]11 and eta1-O[CuNO]11 linkage isomers were calculated at the BPW91/LanL2DZ and 6-311G(df) level. For the most stable eta1-N adduct a clear dependence of the spin density distribution within the Cu-NO moiety on changes in the Cu-N-O angle and the Cu-N bond distance was observed and accounted for by varying spin polarization and delocalization contributions.

The Guanine Cation Radical: Investigation of Deprotonation States by ESR and DFT

PubMed Central

Adhikary, Amitava; Kumar, Anil; Becker, David; Sevilla, Michael D.

2008-01-01

This work reports ESR studies that identify the favored site of deprotonation of the guanine cation radical (G•+) in an aqueous medium at 77 K. Using ESR and UV-visible spectroscopy, one-electron oxidized guanine is investigated in frozen aqueous D2O solutions of 2′-deoxyguanosine (dGuo) at low temperatures at various pHs at which the guanine cation, G•+ (pH 3–5), singly deprotonated species, G(-H)• (pH 7–9) and doubly deprotonated species, G(-2H)•− (pH>11) are found. C-8-deuteration of dGuo to give 8-D-dGuo removes the major proton hyperfine coupling at C-8. This isolates the anisotropic nitrogen couplings for each of the three species and aids our analyses. These anisotropic nitrogen couplings were assigned to specific nitrogen sites by use of 15N substituted derivatives at N1, N2 N3 atoms in dGuo. Both ESR and UV-visible spectra are reported for each of the species: G•+, G(-H)•, and G(-2H)•−. The experimental anisotropic ESR hyperfine couplings are compared to those obtained from DFT calculations for the various tautomers of G(-H)•. Using the B3LYP/6–31G(d) method, the geometries and energies of G•+ and its singly deprotonated state in its two tautomeric forms, G(N1-H)• and G(N2-H)•, were investigated. In a non-hydrated state G(N2-H)• is found to be more stable than G(N1-H)• but on hydration with 7 water molecules G(N1-H)• is found to be more stable than G(N2-H)•. The theoretically calculated hyperfine coupling constants (HFCC) of G•+, G(N1-H)• and G(-2H)•− match the experimentally observed HFCCs best on hydration with 7 or more waters. For G(-2H)•−, the hyperfine coupling constant (HFCC) at the exocyclic nitrogen atom (N2) is especially sensitive to the number of hydrating water molecules; good agreement with experiment is not obtained until 9 or 10 waters of hydration are included. PMID:17125389

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.

Muon contact hyperfine field in metals: A DFT calculation

NASA Astrophysics Data System (ADS)

Onuorah, Ifeanyi John; Bonfà, Pietro; De Renzi, Roberto

2018-05-01

In positive muon spin rotation and relaxation spectroscopy it is becoming customary to take advantage of density functional theory (DFT) based computational methods to aid the experimental data analysis. DFT-aided muon site determination is especially useful for measurements performed in magnetic materials, where large contact hyperfine interactions may arise. Here we present a systematic analysis of the accuracy of the ab initio estimation of muon's hyperfine contact field on elemental transition metals, performing state-of-the-art spin-polarized plane-wave DFT and using the projector-augmented pseudopotential approach, which allows one to include the core state effects due to the spin ordering. We further validate this method in not-so-simple, noncentrosymmetric metallic compounds, presently of topical interest for their spiral magnetic structure giving rise to skyrmion phases, such as MnSi and MnGe. The calculated hyperfine fields agree with experimental values in all cases, provided the spontaneous spin magnetization of the metal is well reproduced within the approach. To overcome the known limits of the conventional mean-field approximation of DFT on itinerant magnets, we adopt the so-called reduced Stoner theory [L. Ortenzi et al., Phys. Rev. B 86, 064437 (2012), 10.1103/PhysRevB.86.064437]. We establish the accuracy of the estimated muon contact field in metallic compounds with DFT and our results show improved agreement with experiments compared to those of earlier publications.

DFT simulation, quantum chemical electronic structure, spectroscopic and structure-activity investigations of 2-benzothiazole acetonitrile.

PubMed

Arjunan, V; Thillai Govindaraja, S; Jose, Sujin P; Mohan, S

2014-07-15

The Fourier transform infrared and FT-Raman spectra of 2-benzothiazole acetonitrile (BTAN) have been recorded in the range 4000-450 and 4000-100 cm(-1) respectively. The conformational analysis of the compound has been carried out to obtain the stable geometry of the compound. The complete vibrational assignment and analysis of the fundamental modes of the compound are carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The experimental vibrational frequencies are compared with the wavenumbers derived theoretically by B3LYP gradient calculations employing the standard 6-31G(**), high level 6-311++G(**) and cc-pVTZ basis sets. The structural parameters, thermodynamic properties and vibrational frequencies of the normal modes obtained from the B3LYP methods are in good agreement with the experimental data. The (1)H (400 MHz; CDCl3) and (13)C (100 MHz;CDCl3) nuclear magnetic resonance (NMR) spectra are also recorded. The electronic properties, the energies of the highest occupied and lowest unoccupied molecular orbitals are measured by DFT approach. The kinetic stability of the molecule has been determined from the frontier molecular orbital energy gap. The charges of the atoms and the structure-chemical reactivity relations of the compound are determined by its chemical potential, global hardness, global softness, electronegativity, electrophilicity and local reactivity descriptors by conceptual DFT methods. The non-linear optical properties of the compound have been discussed by measuring the polarisability and hyperpolarisability tensors. Copyright © 2014 Elsevier B.V. All rights reserved.

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).

A computational DFT study of structural transitions in textured solid-fluid interfaces

NASA Astrophysics Data System (ADS)

Yatsyshin, Petr; Parry, Andrew O.; Kalliadasis, Serafim

2015-11-01

Fluids adsorbed at walls, in capillary pores and slits, and in more exotic, sculpted geometries such as grooves and wedges can exhibit many new phase transitions, including wetting, pre-wetting, capillary-condensation and filling, compared to their bulk counterparts. As well as being of fundamental interest to the modern statistical mechanical theory of inhomogeneous fluids, these are also relevant to nanofluidics, chemical- and bioengineering. In this talk we will show using a microscopic Density Functional Theory (DFT) for fluids how novel, continuous, interfacial transitions associated with the first-order prewetting line, can occur on steps, in grooves and in wedges, that are sensitive to both the range of the intermolecular forces and interfacial fluctuation effects. These transitions compete with wetting, filling and condensation producing very rich phase diagrams even for relatively simple geometries. We will also discuss practical aspects of DFT calculations, and demonstrate how this statistical-mechanical framework is capable of yielding complex fluid structure, interfacial tensions, and regions of thermodynamic stability of various fluid configurations. As a side note, this demonstrates that DFT is an excellent tool for the investigations of complex multiphase systems. We acknowledge financial support from the European Research Council via Advanced Grant No. 247031.

DFT investigation of the interaction of gold nanoclusters with poly(amidoamine) PAMAM G0 dendrimer

NASA Astrophysics Data System (ADS)

Camarada, M. B.

2016-06-01

The interaction between PAMAM G0 and gold nanoclusters Aun (n = 2, 4, 6, and 8) was studied theoretically at DFT level. Different coordination sites were explored, including internal and superficial coordination. All stable complexes exhibited external interaction with the amine or carbonyl site, while the core site coordination was not favored. The more stable binding of Aun was registered with the terminal amine group, while the binding at the amide site was relatively weaker. The vertical first ionization potential, electron affinity, Fermi level, and the HOMO-LUMO gap of PAMAM and Aun-PAMAM G0 complexes were also analyzed.

DFT investigation on the adsorption behavior of dimethyl and trimethyl amine molecules on borophene nanotube

NASA Astrophysics Data System (ADS)

Bhuvaneswari, R.; Chandiramouli, R.

2018-06-01

The electronic properties of borophene nanotube (BNT) are witnessed and the adsorption properties of dimethyl amine (DMA) and trimethyl amine (TMA) molecules on borophene nanotube are explored through non-equilibrium Green's function (NEGF) and density functional theory (DFT) method. The device density of states spectrum interprets the change in peak maxima, thus indicating the electron transition between DMA, TMA molecules and BNT base material. I-V characteristics strengthen the adsorption property of DMA and TMA on BNT by pointing out the variation in the current. The present work assures that borophene nanotube (BNT) can be employed as DMA and TMA sensor.

Charge Transfer Enhancement in the D-π-A Type Porphyrin Dyes: A Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) Study.

PubMed

Kang, Guo-Jun; Song, Chao; Ren, Xue-Feng

2016-11-25

The electronic geometries and optical properties of two D-π-A type zinc porphyrin dyes (NCH₃-YD2 and TPhe-YD) were systematically investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to reveal the origin of significantly altered charge transfer enhancement by changing the electron donor of the famous porphyrin-based sensitizer YD2-o-C8. The molecular geometries and photophysical properties of dyes before and after binding to the TiO₂ cluster were fully investigated. From the analyses of natural bond orbital (NBO), extended charge decomposition analysis (ECDA), and electron density variations (Δρ) between the excited state and ground state, it was found that the introduction of N(CH₃)₂ and 1,1,2-triphenylethene groups enhanced the intramolecular charge-transfer (ICT) character compared to YD2-o-C8. The absorption wavelength and transition possess character were significantly influenced by N(CH₃)₂ and 1,1,2-triphenylethene groups. NCH₃-YD2 with N(CH₃)₂ groups in the donor part is an effective way to improve the interactions between the dyes and TiO₂ surface, light having efficiency (LHE), and free energy change (ΔG inject ), which is expected to be an efficient dye for use in dye-sensitized solar cells (DSSCs).

NSAIDs as potential treatment option for preventing amyloid β toxicity in Alzheimer's disease: an investigation by docking, molecular dynamics, and DFT studies.

PubMed

Azam, Faizul; Alabdullah, Nada Hussin; Ehmedat, Hadeel Mohammed; Abulifa, Abdullah Ramadan; Taban, Ismail; Upadhyayula, Sreedevi

2018-06-01

Aggregation of amyloid beta (Aβ) protein considered as one of contributors in development of Alzheimer's disease (AD). Several investigations have identified the importance of non-steroidal anti-inflammatory drugs (NSAIDs) as Aβ aggregation inhibitors. Here, we have examined the binding interactions of 24 NSAIDs belonging to eight different classes, with Aβ fibrils by exploiting docking and molecular dynamics studies. Minimum energy conformation of the docked NSAIDs were further optimized by density functional theory (DFT) employing Becke's three-parameter hybrid model, Lee-Yang-Parr (B3LYP) correlation functional method. DFT-based global reactivity descriptors, such as electron affinity, hardness, softness, chemical potential, electronegativity, and electrophilicity index were calculated to inspect the expediency of these descriptors for understanding the reactive nature and sites of the molecules. Few selected NSAID-Aβ fibrils complexes were subjected to molecular dynamics simulation to illustrate the stability of these complexes and the most prominent interactions during the simulated trajectory. All of the NSAIDs exhibited potential activity against Aβ fibrils in terms of predicted binding affinity. Sulindac was found to be the most active compound underscoring the contribution of indene methylene substitution, whereas acetaminophen was observed as least active NSAID. General structural requirements for interaction of NSAIDs with Aβ fibril include: aryl/heteroaryl aromatic moiety connected through a linker of 1-2 atoms to a distal aromatic group. Considering these structural requirements and electronic features, new potent agents can be designed and developed as potential Aβ fibril inhibitors for the treatment of AD.

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.

Conformational, spectroscopic and nonlinear optical investigations on 1-(4-chlorophenyl)-3-(4-chlorophenyl)-2-propen-1-one: a DFT study

NASA Astrophysics Data System (ADS)

Altürk, Sümeyye; Boukabcha, Nourdine; Benhalima, Nadia; Tamer, Ömer; Chouaih, Abdelkader; Avcı, Davut; Atalay, Yusuf; Hamzaoui, Fodil

2017-05-01

The density functional theory calculations on 1-(4-chlorophenyl)-3-(4-chlorophenyl)-2-propen-1-one (CPCPP) are performed by using B3LYP and HSEh1PBE levels. These methods along with 6-311++G(d,p) basis set have been used to determine optimized molecular geometries, vibrational frequencies, electronic absorption wavelengths and bonding features of CPCPP. The solvent effect on the electronic absorption properties of CPCPP is examined at polar (ethanol and water) and nonpolar (toluene and n-hexane) solvents. In order to find the most stable conformers, conformational analysis is carried out by using B3LYP level. The computed small energy gaps between HOMO and LUMO energies show that the charge transfers occur within CPCPP. DFT calculations have been also performed to investigate the dipole moment (μ), mean polarizability (α), anisotropy of polarizability (Δα), first order static hyperpolarizability (β) for CPCPP. The obtained values show that CPCPP is an excellent candidate to nonlinear optical materials. NBO analysis has been used to investigate the bond strengths, molecular stability, hyperconjugative interactions and intramolecular charge transfer (ICT).

Methyl cation affinities of neutral and anionic maingroup-element hydrides: trends across the periodic table and correlation with proton affinities.

PubMed

Mulder, R Joshua; Guerra, Célia Fonseca; Bickelhaupt, F Matthias

2010-07-22

We have computed the methyl cation affinities in the gas phase of archetypal anionic and neutral bases across the periodic table using ZORA-relativistic density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. The main purpose of this work is to provide the methyl cation affinities (and corresponding entropies) at 298 K of all anionic (XH(n-1)(-)) and neutral bases (XH(n)) constituted by maingroup-element hydrides of groups 14-17 and the noble gases (i.e., group 18) along the periods 2-6. The cation affinity of the bases decreases from H(+) to CH(3)(+). To understand this trend, we have carried out quantitative bond energy decomposition analyses (EDA). Quantitative correlations are established between the MCA and PA values.

An EQT-cDFT approach to determine thermodynamic properties of confined fluids.

PubMed

Mashayak, S Y; Motevaselian, M H; Aluru, N R

2015-06-28

We present a continuum-based approach to predict the structure and thermodynamic properties of confined fluids at multiple length-scales, ranging from a few angstroms to macro-meters. The continuum approach is based on the empirical potential-based quasi-continuum theory (EQT) and classical density functional theory (cDFT). EQT is a simple and fast approach to predict inhomogeneous density and potential profiles of confined fluids. We use EQT potentials to construct a grand potential functional for cDFT. The EQT-cDFT-based grand potential can be used to predict various thermodynamic properties of confined fluids. In this work, we demonstrate the EQT-cDFT approach by simulating Lennard-Jones fluids, namely, methane and argon, confined inside slit-like channels of graphene. We show that the EQT-cDFT can accurately predict the structure and thermodynamic properties, such as density profiles, adsorption, local pressure tensor, surface tension, and solvation force, of confined fluids as compared to the molecular dynamics simulation results.

Equation of state of mixtures: density functional theory (DFT) simulations and experiments on Sandia's Z machine

NASA Astrophysics Data System (ADS)

Magyar, R. J.; Root, S.; Haill, T. A.; Schroen, D. G.; Mattsson, T. R.; Flicker, D. G.; Sandia National Laboratories Collaboration

2011-06-01

Mixtures of materials are expected to behave quite differently from their isolated constituents, particularly when the constituents atomic numbers differ significantly. To investigate the mixture behavior, we performed density functional theory (DFT) calculations on xenon/hydrogen, xenon/ethane, and platinum/hydrocarbon mixtures. In addition, we performed shock compression experiments on platinum-doped hydrocarbon foams up to 480 GPa using the Sandia Z-accelerator. Since the DFT simulations treat electrons and nuclei generically, simulations of pure and mix systems are expected to be of comparable accuracy. The DFT and experimental results are compared to hydrodynamic simulations using different mixing models in the equation of state. The role of de-mixing and the relative contributions of the enthalpy of mixing are explored. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of the Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Critical analysis of fragment-orbital DFT schemes for the calculation of electronic coupling values

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

Schober, Christoph; Reuter, Karsten; Oberhofer, Harald, E-mail: harald.oberhofer@ch.tum.de

2016-02-07

We present a critical analysis of the popular fragment-orbital density-functional theory (FO-DFT) scheme for the calculation of electronic coupling values. We discuss the characteristics of different possible formulations or “flavors” of the scheme which differ by the number of electrons in the calculation of the fragments and the construction of the Hamiltonian. In addition to two previously described variants based on neutral fragments, we present a third version taking a different route to the approximate diabatic state by explicitly considering charged fragments. In applying these FO-DFT flavors to the two molecular test sets HAB7 (electron transfer) and HAB11 (hole transfer),more » we find that our new scheme gives improved electronic couplings for HAB7 (−6.2% decrease in mean relative signed error) and greatly improved electronic couplings for HAB11 (−15.3% decrease in mean relative signed error). A systematic investigation of the influence of exact exchange on the electronic coupling values shows that the use of hybrid functionals in FO-DFT calculations improves the electronic couplings, giving values close to or even better than more sophisticated constrained DFT calculations. Comparing the accuracy and computational cost of each variant, we devise simple rules to choose the best possible flavor depending on the task. For accuracy, our new scheme with charged-fragment calculations performs best, while numerically more efficient at reasonable accuracy is the variant with neutral fragments.« less

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.

Design Techniques for Uniform-DFT, Linear Phase Filter Banks

NASA Technical Reports Server (NTRS)

Sun, Honglin; DeLeon, Phillip

1999-01-01

Uniform-DFT filter banks are an important class of filter banks and their theory is well known. One notable characteristic is their very efficient implementation when using polyphase filters and the FFT. Separately, linear phase filter banks, i.e. filter banks in which the analysis filters have a linear phase are also an important class of filter banks and desired in many applications. Unfortunately, it has been proved that one cannot design critically-sampled, uniform-DFT, linear phase filter banks and achieve perfect reconstruction. In this paper, we present a least-squares solution to this problem and in addition prove that oversampled, uniform-DFT, linear phase filter banks (which are also useful in many applications) can be constructed for perfect reconstruction. Design examples are included illustrate the methods.

Experimental and DFT study of thiol-stabilized Pt/CNTs catalysts.

PubMed

Li, L; Chen, S G; Wei, Z D; Qi, X Q; Xia, M R; Wang, Y Q

2012-12-28

Using a combination of experiments and density functional theory (DFT) calculations, we explored the mechanisms of the stabilization effect of the thiolized (-SH) group on the Pt/SH-CNTs catalyst. Pt particles supported on the hydroxyl functionalized CNTs (Pt/OH-CNTs) are synthesized as a baseline for comparison. Experimentally, the platinum on OH-CNTs has a stronger tendency for aggregation than that on SH-CNTs. The differences in the oxidation resistance, migration activation energy, and corrosion resistance between the Pt/SH-CNTs and Pt/OH-CNTs are calculated using DFT. The DFT calculations indicate that the -SH group enhances the oxidation resistance of the Pt cluster and CNTs and restricts Pt migration on the CNTs. DFT calculations also suggest that the enhanced stability of Pt/SH-CNTs originates from the increased interaction between Pt and SH-CNTs and the depressed d-band center of the Pt NPs. Thus, the functional groups on the CNTs used for stabilization of supported Pt NPs should provide a deposit and anchor site for Pt NPs and maintain the perfect structure of CNTs rather than destroying it.

GW quasiparticle bandgaps of anatase TiO2 starting from DFT + U.

PubMed

Patrick, Christopher E; Giustino, Feliciano

2012-05-23

We investigate the quasiparticle band structure of anatase TiO(2), a wide gap semiconductor widely employed in photovoltaics and photocatalysis. We obtain GW quasiparticle energies starting from density-functional theory (DFT) calculations including Hubbard U corrections. Using a simple iterative procedure we determine the value of the Hubbard parameter yielding a vanishing quasiparticle correction to the fundamental bandgap of anatase TiO(2). The bandgap (3.3 eV) calculated using this optimal Hubbard parameter is smaller than the value obtained by applying many-body perturbation theory to standard DFT eigenstates and eigenvalues (3.7 eV). We extend our analysis to the rutile polymorph of TiO(2) and reach similar conclusions. Our work highlights the role of the starting non-interacting Hamiltonian in the calculation of GW quasiparticle energies in TiO(2) and suggests an optimal Hubbard parameter for future calculations.

Water Adsorption and Dissociation on Ceria-Supported Single-Atom Catalysts: A First-Principles DFT+U Investigation.

PubMed

Han, Zhong-Kang; Gao, Yi

2016-02-01

Single-atom catalysts have attracted wide attention owing to their extremely high atom efficiency and activities. In this paper, we applied density functional theory with the inclusion of the on-site Coulomb interaction (DFT+U) to investigate water adsorption and dissociation on clean CeO 2 (111) surfaces and single transition metal atoms (STMAs) adsorbed on the CeO 2 (111) surface. It is found that the most stable water configuration is molecular adsorption on the clean CeO 2 (111) surface and dissociative adsorption on STMA/CeO 2 (111) surfaces, respectively. In addition, our results indicate that the more the electrons that transfer from STMA to the ceria substrate, the stronger the binding energies between the STMA and ceria surfaces. A linear relationship is identified between the water dissociation barriers and the d band centers of STMA, known as the generalized Brønsted-Evans-Polanyi principle. By combining the oxygen spillovers, single-atom dispersion stabilities, and water dissociation barriers, Zn, Cr, and V are identified as potential candidates for the future design of ceria-supported single-atom catalysts for reactions in which the dissociation of water plays an important role, such as the water-gas shift reaction. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Water dissociation and CO oxidation over Au/anatase catalyst. A DFT-D2 study

NASA Astrophysics Data System (ADS)

Saqlain, Muhammad Adnan; Hussain, Akhtar; Siddiq, Muhammad; Leitão, Alexandre A.

2018-03-01

With the help of DFT-D2 methodology, we have investigated the adsorption of water on clean anatase(001) and Au/anatase(001). In the former case, adsorption energies of H2O differ to small extent computed employing GGA = PW91 and DFT-D2 methods. While the GGA = PW91 predicts that water would desorb close to 650 K on the TiO2 surface, the DFT-D2 predicts that desorption is most likely to occur above 700 K. A comparison of water adsorption on TiO2 and Au/TiO2 surfaces shows that the TiO2 prefers dimer adsorption whereas the Au/TiO2 prefers monomer adsorption. We found that the diffusion of surface hydroxyls on to the Au cluster from the Au/TiO2 periphery is unlikely and it seems that the CO oxidation would occur at the Au/TiO2 boundary. The results show that water dissociation and CO oxidation steps occur easily on Au/TiO2 indicating that this could be good alternative catalyst for water gas shift reaction industry.

FAST TRACK COMMUNICATION A DFT + DMFT approach for nanosystems

NASA Astrophysics Data System (ADS)

Turkowski, Volodymyr; Kabir, Alamgir; Nayyar, Neha; Rahman, Talat S.

2010-11-01

We propose a combined density-functional-theory-dynamical-mean-field-theory (DFT + DMFT) approach for reliable inclusion of electron-electron correlation effects in nanosystems. Compared with the widely used DFT + U approach, this method has several advantages, the most important of which is that it takes into account dynamical correlation effects. The formalism is illustrated through different calculations of the magnetic properties of a set of small iron clusters (number of atoms 2 <= N <= 5). It is shown that the inclusion of dynamical effects leads to a reduction in the cluster magnetization (as compared to results from DFT + U) and that, even for such small clusters, the magnetization values agree well with experimental estimations. These results justify confidence in the ability of the method to accurately describe the magnetic properties of clusters of interest to nanoscience.

Conformational, vibrational, NMR and DFT studies of N-methylacetanilide.

PubMed

Arjunan, V; Santhanam, R; Rani, T; Rosi, H; Mohan, S

2013-03-01

A detailed conformational, vibrational, NMR and DFT studies of N-methylacetanilide have been carried out. In DFT, B3LYP method have been used with 6-31G(**), 6-311++G(**) and cc-pVTZ basis sets. The vibrational frequencies were calculated resulting in IR and Raman frequencies together with intensities and Raman depolarisation ratios. The dipole moment derivatives were computed analytically. Owing to the complexity of the molecule, the potential energy distributions of the vibrational modes of the compound are also calculated. Isoelectronic molecular electrostatic potential surface (MEP) and electron density surface were examined. (1)H and (13)C NMR isotropic chemical shifts were calculated and the assignments made are compared with the experimental values. The energies of important MO's of the compound were also determined from TD-DFT method. Copyright © 2012 Elsevier B.V. All rights reserved.

Experimental demonstration of OFDM/OQAM transmission with DFT-based channel estimation for visible laser light communications

NASA Astrophysics Data System (ADS)

He, Jing; Shi, Jin; Deng, Rui; Chen, Lin

2017-08-01

Recently, visible light communication (VLC) based on light-emitting diodes (LEDs) is considered as a candidate technology for fifth-generation (5G) communications, VLC is free of electromagnetic interference and it can simplify the integration of VLC into heterogeneous wireless networks. Due to the data rates of VLC system limited by the low pumping efficiency, small output power and narrow modulation bandwidth, visible laser light communication (VLLC) system with laser diode (LD) has paid more attention. In addition, orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) is currently attracting attention in optical communications. Due to the non-requirement of cyclic prefix (CP) and time-frequency domain well-localized pulse shapes, it can achieve high spectral efficiency. Moreover, OFDM/OQAM has lower out-of-band power leakage so that it increases the system robustness against inter-carrier interference (ICI) and frequency offset. In this paper, a Discrete Fourier Transform (DFT)-based channel estimation scheme combined with the interference approximation method (IAM) is proposed and experimentally demonstrated for VLLC OFDM/OQAM system. The performance of VLLC OFDM/OQAM system with and without DFT-based channel estimation is investigated. Moreover, the proposed DFT-based channel estimation scheme and the intra-symbol frequency-domain averaging (ISFA)-based method are also compared for the VLLC OFDM/OQAM system. The experimental results show that, the performance of EVM using the DFT-based channel estimation scheme is improved about 3dB compared with the conventional IAM method. In addition, the DFT-based channel estimation scheme can resist the channel noise effectively than that of the ISFA-based method.

Synthesis and DFT calculations of some 2-aminothiazoles

NASA Astrophysics Data System (ADS)

Rezania, Jafar; Behzadi, Hadi; Shockravi, Abbas; Ehsani, Morteza; Akbarzadeh, Elahe

2018-04-01

A series of 2-aminothiazole derivatives have been synthesized by the reaction of acetyl compounds with thiourea and iodine as catalyst under solvent-free condition, a green chemistry method. The quantum chemical calculations at the DFT/B3LYP level of theory in gas phase were carried out for starting acetyl derivatives. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and related reactivity descriptor of acetyl derivatives, as well as, enthalpy of reactions are calculated in order to investigate the reaction properties of acetyl compounds and yields of the reactions. The calculated reactivity descriptors are well correlated to activity of different acetyl derivatives.

Implementation of DFT application on ternary optical computer

NASA Astrophysics Data System (ADS)

Junjie, Peng; Youyi, Fu; Xiaofeng, Zhang; Shuai, Kong; Xinyu, Wei

2018-03-01

As its characteristics of huge number of data bits and low energy consumption, optical computing may be used in the applications such as DFT etc. which needs a lot of computation and can be implemented in parallel. According to this, DFT implementation methods in full parallel as well as in partial parallel are presented. Based on resources ternary optical computer (TOC), extensive experiments were carried out. Experimental results show that the proposed schemes are correct and feasible. They provide a foundation for further exploration of the applications on TOC that needs a large amount calculation and can be processed in parallel.

The structural and spectroscopic investigation of 2-chloro-3-methylquinoline by DFT method and UV-Vis, NMR and vibrational spectral techniques combined with molecular docking analysis

NASA Astrophysics Data System (ADS)

Kose, Etem; Atac, Ahmet; Bardak, Fehmi

2018-07-01

This study comprises the structural and spectroscopic evaluation of a quinoline derivative, 2-chloro-3-methylquinoline (2Cl3MQ), via UV-Vis, 1H and 13C NMR, FT-IR and FT-Raman techniques experimentally, theoretically with DFT and TD-DFT quantum chemical calculations at B3LYP/6-311++G (d, p) level of theory, and investigation of the in silico pharmaceutical potent of 2Cl3MQ in comparison to 2ClnMQ (n = 3,4,7,8,9,10) substituted quinolines. The experimental measurements were recorded as follows; UV-vis spectra were obtained in the range of 200-400 nm in the water and ethanol solvents. 1H and 13C NMR spectra were recorded in CDCl3. Vibrational spectra were obtained in the region of 4000-400 cm-1 and 3500-10 cm-1 for FT-IR and FT-Raman spectra, respectively. Structural and spectroscopic features obtained through theoretical evaluations include: electrostatic features, atomic charges and molecular electrostatic potential surface, the frontier molecular orbital characteristics, the density of states and their overlapping nature, the electronic transition properties, thermodynamical and nonlinear optical characteristics, and predicted UV-Vis, 1H and 13C NMR, FT-IR and FT-Raman spectra. Ligand-enzyme interactions of 2ClnMQ (n = 3,4,7,8,9,10) substituted quinolines with Malate Synthase from Mycobacterium Tuberculosis (MtbMS) were investigated via molecular docking. The role of position of methyl substitution on the inhibitor character of the ligands was discussed on the basis of noncovalent interaction profiles.

Why is MP2-Water "Cooler" and "Denser" than DFT-Water?

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

Willow, Soohaeng Y.; Zeng, Xiao Cheng; Xantheas, Sotiris S.

To maintain water in the liquid phase at the correct (1 g/cm3) density during first-principles simulations, density-functional theory (DFT) with a dispersionless generalized-gradient-approximation (GGA) functional requires a much higher temperature and pressure than the ambient conditions. Conversely, ab initio second-order many-body perturbation (MP2) calculations of liquid water performed by Del Ben et al. [J. Chem. Phys. Lett. 4, 3753 (2013); J. Chem. Phys. 143, 054506 (2015)] and by us [Willow et al., Sci. Rep. 5, 14358 (2015)] required a lower temperature and a negative pressure than DFT to keep water liquid. Here, we present a unifying explanation of these trendsmore » derived from classical water simulations using a polarizable force field with different sets of parameters. We show that the calculated temperature and pressure of the liquid phase are strongly correlated with the polarizability of water and the dispersion interaction, respectively. In DFT/GGA, the polarizability and thus the induced dipole moments and the hydrogen-bond strength are all overestimated. This hinders the rotational motion of molecules and requires a higher temperature for water to be liquid. In MP2 and DFT/GGA, the dispersion interaction is stronger and weaker (or lacking), respectively. This explains why liquid water contracts uniformly and becomes too dense in MP2, whereas the opposite is the case for dispersionless DFT/GGA.« 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.

On the number of multiplications necessary to compute a length-2 exp n DFT

NASA Technical Reports Server (NTRS)

Heideman, M. T.; Burrus, C. S.

1986-01-01

The number of multiplications necessary and sufficient to compute a length-2 exp n DFT is determined. The method of derivation is shown to apply to the multiplicative complexity results of Winograd (1980, 1981) for a length-p exp n DFT, for p an odd prime number. The multiplicative complexity of the one-dimensional DFT is summarized for many possible lengths.

Adaptive DFT-based Interferometer Fringe Tracking

NASA Technical Reports Server (NTRS)

Wilson, Edward; Pedretti, Ettore; Bregman, Jesse; Mah, Robert W.; Traub, Wesley A.

2004-01-01

An automatic interferometer fringe tracking system has been developed, implemented, and tested at the Infrared Optical Telescope Array (IOTA) observatory at Mt. Hopkins, Arizona. The system can minimize the optical path differences (OPDs) for all three baselines of the Michelson stellar interferometer at IOTA. Based on sliding window discrete Fourier transform (DFT) calculations that were optimized for computational efficiency and robustness to atmospheric disturbances, the algorithm has also been tested extensively on off-line data. Implemented in ANSI C on the 266 MHz PowerPC processor running the VxWorks real-time operating system, the algorithm runs in approximately 2.0 milliseconds per scan (including all three interferograms), using the science camera and piezo scanners to measure and correct the OPDs. The adaptive DFT-based tracking algorithm should be applicable to other systems where there is a need to detect or track a signal with an approximately constant-frequency carrier pulse.

Theoretical investigation of structures and energetics of sodium adatom and its dimer on graphene: DFT study

NASA Astrophysics Data System (ADS)

Kaur, Gagandeep; Gupta, Shuchi; Rani, Pooja; Dharamvir, Keya

2015-11-01

Extensive ab initio calculations have been performed to study the energetics of a sodium (Na) atom and its dimer adsorbed on graphene using the SIESTA package Soler et al. (2002) [1] which works within a DFT(density functional theory)-GGA (generalized gradient approximation) pseudopotential framework. The adsorption energy, geometry, charge transfer, ionization potential and density of states (DOS), partial density states (PDOS) of adatom/dimer-graphene system have been calculated. After considering various sites for adsorption of Na on graphene, the center of a hexagonal ring of carbon atoms is found to be the preferred site of adsorption while the Na2 dimer prefers to rest parallel to the graphene sheet. We find insignificant energy differences among adsorption configurations involving different possible sites in parallel orientation, which implies high mobility of the dimer on the graphene sheet. We also notice only a slight distortion of the graphene sheet perpendicular to its plane upon adatom adsorption. However, some lateral displacements seen are more perceptible. Summary The adsorption energy, geometry, charge transfer, ionization potential and density of states (DOS) and PDOS of adatom/dimer-graphene system have been calculated using SIESTA package Soler et al. (2002) [1] which works within a DFT(density functional theory)-GGA (generalized gradient approximation) pseudopotential framework. Preferred site for adsorption of a sodium atom on graphene is the hollow site. For the Na dimer adsorption, we found that horizontal orientation is favored over the vertical one. From DOS plots, it is clear that graphene's states are nearly unaffected by the adsorption of Na adatom and Interaction between sodium and graphene is predominantly ionic

Embedding multiple watermarks in the DFT domain using low- and high-frequency bands

NASA Astrophysics Data System (ADS)

Ganic, Emir; Dexter, Scott D.; Eskicioglu, Ahmet M.

2005-03-01

Although semi-blind and blind watermarking schemes based on Discrete Cosine Transform (DCT) or Discrete Wavelet Transform (DWT) are robust to a number of attacks, they fail in the presence of geometric attacks such as rotation, scaling, and translation. The Discrete Fourier Transform (DFT) of a real image is conjugate symmetric, resulting in a symmetric DFT spectrum. Because of this property, the popularity of DFT-based watermarking has increased in the last few years. In a recent paper, we generalized a circular watermarking idea to embed multiple watermarks in lower and higher frequencies. Nevertheless, a circular watermark is visible in the DFT domain, providing a potential hacker with valuable information about the location of the watermark. In this paper, our focus is on embedding multiple watermarks that are not visible in the DFT domain. Using several frequency bands increases the overall robustness of the proposed watermarking scheme. Specifically, our experiments show that the watermark embedded in lower frequencies is robust to one set of attacks, and the watermark embedded in higher frequencies is robust to a different set of attacks.

Absorption and emission spectroscopic characteristics of dipterex and its molecularly imprinted recognition: A TD-DFT investigation

NASA Astrophysics Data System (ADS)

Cheng, Xueli; Li, Liqing; Zhao, Yanyun; Wang, Chang'an

2016-05-01

By using G09 program package, the absorption and fluorescence/phosphorescence spectra of dipterex were explored, and its spectroscopic characters were altered by methacrylic acid (MAA) as the imprinted molecule. The TD-DFT results revealed that: (1) All absorption and emission excitations of dipterex are assigned to the nσ∗ transition; (2) without MAA as imprinted molecule, one of the dipterex Csbnd Cl bonds is extended significantly and dipterex is almost destroyed in transition states; (3) dipterex is connected to methacrylic acid via two hydrogen bonds; (4) for the dipterex-MAA complex, the electronic excitation (ππ∗ excitation) in absorption spectra is dominated by the configuration HOMO → LUMO.

Structure-activity relations of 2-(methylthio)benzimidazole by FTIR, FT-Raman, NMR, DFT and conceptual DFT methods.

PubMed

Arjunan, V; Raj, Arushma; Ravindran, P; Mohan, S

2014-01-24

The vibrational fundamental modes of 2-(methylthio)benzimidazole (2MTBI) have been analysed by combining FTIR, FT-Raman and quantum chemical calculations. The structural parameters of the compound are determined from the optimised geometry by B3LYP with 6-31G(∗∗), 6-311++G(∗∗) and cc-pVTZ basis sets and giving energies, harmonic vibrational frequencies, depolarisation ratios, IR intensities and Raman activities. (1)H and (13)C NMR spectra have been analysed and (1)H and (13)C nuclear magnetic resonance chemical shifts are calculated using the gauge independent atomic orbital (GIAO) method. The structure-activity relationship of the compound is also investigated by conceptual DFT methods. The chemical reactivity and site selectivity of the molecule has been determined with the help of global and local reactivity descriptors. Copyright © 2013 Elsevier B.V. All rights reserved.

Benchmarking Hydrogen and Carbon NMR Chemical Shifts at HF, DFT, and MP2 Levels.

PubMed

Flaig, Denis; Maurer, Marina; Hanni, Matti; Braunger, Katharina; Kick, Leonhard; Thubauville, Matthias; Ochsenfeld, Christian

2014-02-11

An extensive study of error distributions for calculating hydrogen and carbon NMR chemical shifts at Hartree-Fock (HF), density functional theory (DFT), and Møller-Plesset second-order perturbation theory (MP2) levels is presented. Our investigation employs accurate CCSD(T)/cc-pVQZ calculations for providing reference data for 48 hydrogen and 40 carbon nuclei within an extended set of chemical compounds covering a broad range of the NMR scale with high relevance to chemical applications, especially in organic chemistry. Besides the approximations of HF, a variety of DFT functionals, and conventional MP2, we also present results with respect to a spin component-scaled MP2 (GIAO-SCS-MP2) approach. For each method, the accuracy is analyzed in detail for various basis sets, allowing identification of efficient combinations of method and basis set approximations.

A fast D.F.T. algorithm using complex integer transforms

NASA Technical Reports Server (NTRS)

Reed, I. S.; Truong, T. K.

1978-01-01

Winograd (1976) has developed a new class of algorithms which depend heavily on the computation of a cyclic convolution for computing the conventional DFT (discrete Fourier transform); this new algorithm, for a few hundred transform points, requires substantially fewer multiplications than the conventional FFT algorithm. Reed and Truong have defined a special class of finite Fourier-like transforms over GF(q squared), where q = 2 to the p power minus 1 is a Mersenne prime for p = 2, 3, 5, 7, 13, 17, 19, 31, 61. In the present paper it is shown that Winograd's algorithm can be combined with the aforementioned Fourier-like transform to yield a new algorithm for computing the DFT. A fast method for accurately computing the DFT of a sequence of complex numbers of very long transform-lengths is thus obtained.

Relationship between Solvation Thermodynamics from IST and DFT Perspectives.

PubMed

Levy, Ronald M; Cui, Di; Zhang, Bin W; Matubayasi, Nobuyuki

2017-04-20

Inhomogeneous solvation theory (IST) and classical density functional theory (DFT) each provide a framework for relating distribution functions of solutions to their thermodynamic properties. As reviewed in this work, both IST and DFT can be formulated in a way that use two "end point" simulations, one of the pure solvent and the other of the solution, to determine the solute chemical potential and other thermodynamic properties of the solution and of subvolumes in regions local to the solute containing hydrating waters. In contrast to IST, where expressions for the excess energy and entropy of solution are the object of analysis, in the DFT end point formulation of the problem, the solute-solvent potential of mean force (PMF) plays a central role. The indirect part of the PMF corresponds to the lowest order (1-body) truncation of the IST expression. Because the PMF is a free energy function, powerful numerical methods can be used to estimate it. We show that the DFT expressions for the solute excess chemical potential can be written in a form which is local, involving integrals only over regions proximate to the solute. The DFT end point route to estimating solvation free energies provides an alternative path to that of IST for analyzing solvation effects on molecular recognition and conformational changes in solution, which can lead to new insights. In order to illustrate the kind of information that is contained in the solute-solvent PMF, we have carried out simulations of β-cyclodextrin in water. This solute is a well studied "host" molecule to which "guest" molecules bind; host-guest systems serve as models for molecular recognition. We illustrate the range of values the direct and indirect parts of the solute-solvent PMF can have as a water molecule is brought to the interface of β-cyclodextrin from the bulk; we discuss the "competition" between these two terms, and the role it plays in molecular recognition.

First example of a high-level correlated calculation of the indirect spin-spin coupling constants involving tellurium: tellurophene and divinyl telluride.

PubMed

Rusakov, Yury Yu; Krivdin, Leonid B; Østerstrøm, Freja F; Sauer, Stephan P A; Potapov, Vladimir A; Amosova, Svetlana V

2013-08-21

This paper documents the very first example of a high-level correlated calculation of spin-spin coupling constants involving tellurium taking into account relativistic effects, vibrational corrections and solvent effects for medium sized organotellurium molecules. The (125)Te-(1)H spin-spin coupling constants of tellurophene and divinyl telluride were calculated at the SOPPA and DFT levels, in good agreement with experimental data. A new full-electron basis set, av3z-J, for tellurium derived from the "relativistic" Dyall's basis set, dyall.av3z, and specifically optimized for the correlated calculations of spin-spin coupling constants involving tellurium was developed. The SOPPA method shows a much better performance compared to DFT, if relativistic effects calculated within the ZORA scheme are taken into account. Vibrational and solvent corrections are next to negligible, while conformational averaging is of prime importance in the calculation of (125)Te-(1)H spin-spin couplings. Based on the performed calculations at the SOPPA(CCSD) level, a marked stereospecificity of geminal and vicinal (125)Te-(1)H spin-spin coupling constants originating in the orientational lone pair effect of tellurium has been established, which opens a new guideline in organotellurium stereochemistry.

Secure Image Transmission over DFT-precoded OFDM-VLC systems based on Chebyshev Chaos scrambling

NASA Astrophysics Data System (ADS)

Wang, Zhongpeng; Qiu, Weiwei

2017-08-01

This paper proposes a physical layer image secure transmission scheme for discrete Fourier transform (DFT) precoded OFDM-based visible light communication systems by using Chebyshev chaos maps. In the proposed scheme, 256 subcarriers and QPSK modulation are employed. The transmitted digital signal of the image is encrypted with a Chebyshev chaos sequence. The encrypted signal is then transformed by a DFT precoding matrix to reduce the PAPR of the OFDM signal. After that, the encrypted and DFT-precoded OFDM are transmitted over a VLC channel. The simulation results show that the proposed image security transmission scheme can not only protect the DFT-precoded OFDM-based VLC from eavesdroppers but also improve BER performance.

Spectroscopic (FT-IR and UV-Vis) and theoretical (HF and DFT) investigation of 2-Ethyl-N-[(5-nitrothiophene-2-yl)methylidene]aniline

NASA Astrophysics Data System (ADS)

Ceylan, Ümit; Tarı, Gonca Özdemir; Gökce, Halil; Ağar, Erbil

2016-04-01

Crystal structure of the title compound, 2-Ethyl-N-[(5-nitrothiophene-2-yl)methylidene]aniline, C13H12N2O2S, has been synthesized and characterized by FT-IR and UV-Vis spectrum. The compound crystallized in the monoclinic space group P 21/c with a = 11.3578 (4) Å, b = 7.4923 (2) Å, c = 14.9676 (6) Å and β = 99.589 (3)° and Z = 4 in the unit cell. The molecular geometry was also calculated using the Gaussian 03 software and structure was optimized using the HF and DFT/B3LYP methods with the 6-311++G(d,p) basis set in ground state. Using the TD-DFT method, the electronic absorption spectra of the title compound was computed in both the gas phase and ethanol solvent. The harmonic vibrational frequencies of the title compound were calculated using the same methods with the 6-311++G(d,p) basis set. The calculated results were compared with the experimental determination results of the compound. It was seen that the optimized structure was in excellent agreement with the X-ray crystal structure. The energetic behaviors of the title compound in solvent media were examined using the HF and DFT/B3LYP methods with the 6-311++G(d,p) basis set applying the polarizable continuum model (PCM). In addition, the molecular orbitals (FMOs) analysis, molecular electrostatic potential (MEP), nonlinear optical and thermodynamic properties of the title compound were performed using the same methods with the 6-311++G(d,p) basis set.

Computational study of AuSi{sub n} (n=1-9) nanoalloy clusters invoking DFT based descriptors

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

Ranjan, Prabhat; Kumar, Ajay; Chakraborty, Tanmoy, E-mail: tanmoy.chakraborty@jaipur.manipal.edu, E-mail: tanmoychem@gmail.com

2016-04-13

Nanoalloy clusters formed between Au and Si are topics of great interest today from both scientific and technological point of view. Due to its remarkable catalytic, electronic, mechanical and magnetic properties Au-Si nanoalloy clusters have extensive applications in the field of microelectronics, catalysis, biomedicine, and jewelry industry. Density Functional Theory (DFT) is a new paradigm of quantum mechanics, which is very much popular to study the electronic properties of materials. Conceptual DFT based descriptors have been invoked to correlate the experimental properties of nanoalloy clusters. In this venture, we have systematically investigated AuSi{sub n} (n=1-9) nanoalloy clusters in the theoreticalmore » frame of the B3LYP exchange correlation. The experimental properties of AuSi{sub n} (n=1-9) nanoalloy clusters are correlated in terms of DFT based descriptors viz. HOMO-LUMO gap, Electronegativity (χ), Global Hardness (η), Global Softness (S) and Electrophilicity Index (ω). The calculated HOMO-LUMO gap exhibits interesting odd-even alteration behaviour, indicating that even numbered clusters possess higher stability as compare to their neighbour odd numbered clusters. This study also reflects a very well agreement between experimental bond length and computed data.« less

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.

Relativistic calculation of nuclear magnetic shielding using normalized elimination of the small component

NASA Astrophysics Data System (ADS)

Kudo, K.; Maeda, H.; Kawakubo, T.; Ootani, Y.; Funaki, M.; Fukui, H.

2006-06-01

The normalized elimination of the small component (NESC) theory, recently proposed by Filatov and Cremer [J. Chem. Phys. 122, 064104 (2005)], is extended to include magnetic interactions and applied to the calculation of the nuclear magnetic shielding in HX (X =F,Cl,Br,I) systems. The NESC calculations are performed at the levels of the zeroth-order regular approximation (ZORA) and the second-order regular approximation (SORA). The calculations show that the NESC-ZORA results are very close to the NESC-SORA results, except for the shielding of the I nucleus. Both the NESC-ZORA and NESC-SORA calculations yield very similar results to the previously reported values obtained using the relativistic infinite-order two-component coupled Hartree-Fock method. The difference between NESC-ZORA and NESC-SORA results is significant for the shieldings of iodine.

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.

Synthesis, molecular structure, FT-IR and XRD investigations of 2-(4-chlorophenyl)-2-oxoethyl 2-chlorobenzoate: a comparative DFT study.

PubMed

Chidan Kumar, C S; Fun, Hoong Kun; Tursun, Mahir; Ooi, Chin Wei; Chandraju, Siddegowda; Quah, Ching Kheng; Parlak, Cemal

2014-04-24

2-(4-Chlorophenyl)-2-oxoethyl 2-chlorobenzoate has been synthesized, its structural and vibrational properties have been reported using FT-IR and single-crystal X-ray diffraction (XRD) studies. The conformational analysis, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of the synthesized compound (C15H10Cl2O3) have been examined by means of Becke-3-Lee-Yang-Parr (B3LYP) density functional theory (DFT) method together with 6-31++G(d,p) basis set. Furthermore, reliable conformational investigation and vibrational assignments have been made by the potential energy surface (PES) and potential energy distribution (PED) analyses, respectively. Calculations are performed with two possible conformations. The title compound crystallizes in orthorhombic space group Pbca with the unit cell dimensions a=12.312(5) Å, b=8.103(3) Å, c=27.565(11) Å, V=2750.0(19) Å(3). B3LYP method provides satisfactory evidence for the prediction of vibrational wavenumbers and structural parameters. Copyright © 2014 Elsevier B.V. All rights reserved.

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

Accurate Energies and Orbital Description in Semi-Local Kohn-Sham DFT

NASA Astrophysics Data System (ADS)

Lindmaa, Alexander; Kuemmel, Stephan; Armiento, Rickard

2015-03-01

We present our progress on a scheme in semi-local Kohn-Sham density-functional theory (KS-DFT) for improving the orbital description while still retaining the level of accuracy of the usual semi-local exchange-correlation (xc) functionals. DFT is a widely used tool for first-principles calculations of properties of materials. A given task normally requires a balance of accuracy and computational cost, which is well achieved with semi-local DFT. However, commonly used semi-local xc functionals have important shortcomings which often can be attributed to features of the corresponding xc potential. One shortcoming is an overly delocalized representation of localized orbitals. Recently a semi-local GGA-type xc functional was constructed to address these issues, however, it has the trade-off of lower accuracy of the total energy. We discuss the source of this error in terms of a surplus energy contribution in the functional that needs to be accounted for, and offer a remedy for this issue which formally stays within KS-DFT, and, which does not harshly increase the computational effort. The end result is a scheme that combines accurate total energies (e.g., relaxed geometries) with an improved orbital description (e.g., improved band structure).

Adaptive DFT-Based Interferometer Fringe Tracking

NASA Astrophysics Data System (ADS)

Wilson, Edward; Pedretti, Ettore; Bregman, Jesse; Mah, Robert W.; Traub, Wesley A.

An automatic interferometer fringe tracking system has been developed, implemented, and tested at the Infrared Optical Telescope Array (IOTA) Observatory at Mount Hopkins, Arizona. The system can minimize the optical path differences (OPDs) for all three baselines of the Michelson stellar interferometer at IOTA. Based on sliding window discrete Fourier-transform (DFT) calculations that were optimized for computational efficiency and robustness to atmospheric disturbances, the algorithm has also been tested extensively on offline data. Implemented in ANSI C on the 266 MHz PowerPC processor running the VxWorks real-time operating system, the algorithm runs in approximately 2.0 milliseconds per scan (including all three interferograms), using the science camera and piezo scanners to measure and correct the OPDs. The adaptive DFT-based tracking algorithm should be applicable to other systems where there is a need to detect or track a signal with an approximately constant-frequency carrier pulse. One example of such an application might be to the field of thin-film measurement by ellipsometry, using a broadband light source and a Fourier-transform spectrometer to detect the resulting fringe patterns.

Structure, electronic and magnetic properties of Mn{sub n} (n=2-8) clusters: A DFT investigation

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

Kumar, Vipin; Roy, Debesh R., E-mail: drr@ashd.svnit.ac.in

2016-05-06

A detail studyon the stability, electronic and magnetic properties of Mn{sub n} (n=2-8) cluster series is performed under the utilization ofdensity functional theory (DFT). The binding energy (B.E.), HOMO-LUMO energy gap (HLG), chemical hardness (η), ionization potential (I.P.), electron affinity (E.A)and electronegativity (χ) of these clusters are predicted. We have also studied the magnetic moments associated with the stable cluster isomers. The lowest energy structures for each cluster sizes aredetermined with a systematic search imposing all possible initial magnetic configuration on the cluster. All the calculations are carried out using a popular GGA functional PBE as proposed by Pardew, Burkemore » and Ernzerhof and implemented in the VASP program.« less

Quantitative structure-activity relationships of the antimalarial agent artemisinin and some of its derivatives - a DFT approach.

PubMed

Rajkhowa, Sanchaita; Hussain, Iftikar; Hazarika, Kalyan K; Sarmah, Pubalee; Deka, Ramesh Chandra

2013-09-01

Artemisinin form the most important class of antimalarial agents currently available, and is a unique sesquiterpene peroxide occurring as a constituent of Artemisia annua. Artemisinin is effectively used in the treatment of drug-resistant Plasmodium falciparum and because of its rapid clearance of cerebral malaria, many clinically useful semisynthetic drugs for severe and complicated malaria have been developed. However, one of the major disadvantages of using artemisinins is their poor solubility either in oil or water and therefore, in order to overcome this difficulty many derivatives of artemisinin were prepared. A comparative study on the chemical reactivity of artemisinin and some of its derivatives is performed using density functional theory (DFT) calculations. DFT based global and local reactivity descriptors, such as hardness, chemical potential, electrophilicity index, Fukui function, and local philicity calculated at the optimized geometries are used to investigate the usefulness of these descriptors for understanding the reactive nature and reactive sites of the molecules. Multiple regression analysis is applied to build up a quantitative structure-activity relationship (QSAR) model based on the DFT based descriptors against the chloroquine-resistant, mefloquine-sensitive Plasmodium falciparum W-2 clone.

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.

PubMed

Bendjabeur, Seyfeddine; Zouaghi, Razika; Zouchoune, Bachir; Sehili, Tahar

2018-02-05

TiO 2 -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 (365nm) and UV-C (254nm) light alone and UV-A in the presence of TiO 2 ·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 (254nm) was found better than under UV-A 365nm. 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. Copyright © 2017. Published by Elsevier B.V.

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.

Ethane and Xenon mixing: density functional theory (DFT) simulations and experiments on Sandia's Z machine

NASA Astrophysics Data System (ADS)

Magyar, Rudolph; Root, Seth; Mattsson, Thomas; Cochrane, Kyle

2012-02-01

The combination of ethane and xenon is one of the simplest binary mixtures in which bond breaking is expected to play a role under shock conditions. At cryogenic conditions, xenon is often understood to mix with alkanes such as Ethane as if it were also an alkane, but this model is expected to break down at higher temperatures and pressures. To investigate the breakdown, we have performed density functional theory (DFT) calculations on several xenon/ethane mixtures. Additionally, we have performed shock compression experiments on Xenon-Ethane using the Sandia Z - accelerator. The DFT and experimental results are compared to hydrodynamic simulations using different mixing models in the equation of state. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of the Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Analyzing the errors of DFT approximations for compressed water systems

NASA Astrophysics Data System (ADS)

Alfè, D.; Bartók, A. P.; Csányi, G.; Gillan, M. J.

2014-07-01

We report an extensive study of the errors of density functional theory (DFT) approximations for compressed water systems. The approximations studied are based on the widely used PBE and BLYP exchange-correlation functionals, and we characterize their errors before and after correction for 1- and 2-body errors, the corrections being performed using the methods of Gaussian approximation potentials. The errors of the uncorrected and corrected approximations are investigated for two related types of water system: first, the compressed liquid at temperature 420 K and density 1.245 g/cm3 where the experimental pressure is 15 kilobars; second, thermal samples of compressed water clusters from the trimer to the 27-mer. For the liquid, we report four first-principles molecular dynamics simulations, two generated with the uncorrected PBE and BLYP approximations and a further two with their 1- and 2-body corrected counterparts. The errors of the simulations are characterized by comparing with experimental data for the pressure, with neutron-diffraction data for the three radial distribution functions, and with quantum Monte Carlo (QMC) benchmarks for the energies of sets of configurations of the liquid in periodic boundary conditions. The DFT errors of the configuration samples of compressed water clusters are computed using QMC benchmarks. We find that the 2-body and beyond-2-body errors in the liquid are closely related to similar errors exhibited by the clusters. For both the liquid and the clusters, beyond-2-body errors of DFT make a substantial contribution to the overall errors, so that correction for 1- and 2-body errors does not suffice to give a satisfactory description. For BLYP, a recent representation of 3-body energies due to Medders, Babin, and Paesani [J. Chem. Theory Comput. 9, 1103 (2013)] gives a reasonably good way of correcting for beyond-2-body errors, after which the remaining errors are typically 0.5 mEh ≃ 15 meV/monomer for the liquid and the

Analyzing the errors of DFT approximations for compressed water systems

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

Alfè, D.; London Centre for Nanotechnology, UCL, London WC1H 0AH; Thomas Young Centre, UCL, London WC1H 0AH

We report an extensive study of the errors of density functional theory (DFT) approximations for compressed water systems. The approximations studied are based on the widely used PBE and BLYP exchange-correlation functionals, and we characterize their errors before and after correction for 1- and 2-body errors, the corrections being performed using the methods of Gaussian approximation potentials. The errors of the uncorrected and corrected approximations are investigated for two related types of water system: first, the compressed liquid at temperature 420 K and density 1.245 g/cm{sup 3} where the experimental pressure is 15 kilobars; second, thermal samples of compressed watermore » clusters from the trimer to the 27-mer. For the liquid, we report four first-principles molecular dynamics simulations, two generated with the uncorrected PBE and BLYP approximations and a further two with their 1- and 2-body corrected counterparts. The errors of the simulations are characterized by comparing with experimental data for the pressure, with neutron-diffraction data for the three radial distribution functions, and with quantum Monte Carlo (QMC) benchmarks for the energies of sets of configurations of the liquid in periodic boundary conditions. The DFT errors of the configuration samples of compressed water clusters are computed using QMC benchmarks. We find that the 2-body and beyond-2-body errors in the liquid are closely related to similar errors exhibited by the clusters. For both the liquid and the clusters, beyond-2-body errors of DFT make a substantial contribution to the overall errors, so that correction for 1- and 2-body errors does not suffice to give a satisfactory description. For BLYP, a recent representation of 3-body energies due to Medders, Babin, and Paesani [J. Chem. Theory Comput. 9, 1103 (2013)] gives a reasonably good way of correcting for beyond-2-body errors, after which the remaining errors are typically 0.5 mE{sub h} ≃ 15 meV/monomer for the

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.

Phenothiazine-anthraquinone donor-acceptor molecules: synthesis, electronic properties and DFT-TDDFT computational study.

PubMed

Zhang, Wen-Wei; Mao, Wei-Li; Hu, Yun-Xia; Tian, Zi-Qi; Wang, Zhi-Lin; Meng, Qing-Jin

2009-09-17

Two donor-acceptor molecules with different pi-electron conjugative units, 1-((10-methyl-10H-phenothiazin-3-yl)ethynyl)anthracene-9,10-dione (AqMp) and 1,1'-(10-methyl-10H-phenothiazine-3,7-diyl)bis(ethyne-2,1-diyl)dianthracene-9,10-dione (Aq2Mp), have been synthesized and investigated for their photochemical and electrochemical properties. Density functional theory (DFT) calculations provide insights into their molecular geometry, electronic structures, and properties. These studies satisfactorily explain the electrochemistry of the two compounds and indicate that larger conjugative effect leads to smaller HOMO-LUMO gap (Eg) in Aq2Mp. Both compounds show ICT and pi --> pi* transitions in the UV-visible range in solution, and Aq2Mp has a bathochromic shift and shows higher oscillator strength of the absorption, which has been verified by time-dependent DFT (TDDFT) calculations. The differences between AqMp and Aq2Mp indicate that the structural and conjugative effects have great influence on the electronic properties of the molecules.

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.

Vibrational spectroscopy (FT-IR and FT-Raman) investigation, and hybrid computational (HF and DFT) analysis on the structure of 2,3-naphthalenediol.

PubMed

Shoba, D; Periandy, S; Karabacak, M; Ramalingam, S

2011-12-01

The FT-IR and FT-Raman vibrational spectra of 2,3-naphthalenediol (C(10)H(8)O(2)) have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1) in solid phase. A detailed vibrational spectral analysis has been carried out and the assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-Fock (HF) and DFT (LSDA and B3LYP) methods with 6-31+G(d,p) and 6-311+G(d,p) basis sets. There are three conformers, C1, C2 and C3 for this molecule. The computational results diagnose the most stable conformer of title molecule as the C1 form. The isotropic computational analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by HF and DFT methods. Comparison of the simulated spectra provides important information about the capability of computational method to describe the vibrational modes. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and Frontier molecular orbital energies, are performed by time dependent DFT approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated. The statistical thermodynamic properties (standard heat capacities, standard entropies, and standard enthalpy changes) and their correlations with temperature have been obtained from the theoretical vibrations. Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

The solvent effects on dimethyl phthalate investigated by FTIR characterization, solvent parameter correlation and DFT computation

NASA Astrophysics Data System (ADS)

Chen, Yi; Zhang, Hui; Zhou, Wenzhao; Deng, Chao; Liao, Jian

2018-06-01

This study set out with the aim of investigating the solvent effects on dimethyl phthalate (DMP) using FTIR characterization, solvent parameter correlation and DFT calculation. DMP exposed to 17 organic solvents manifested varying shift in the carbonyl stretching vibration frequency (νCdbnd O). Non-alkanols induced Band I and alkanols produced Band I and Band II. Through correlating the νCdbnd O with the empirical solvent scales including acceptor parameter (AN), Schleyer's linear free energy parameter (G), and linear free salvation energy relationships (LSER), Band I was mainly ascribed to non-specific effects from either non-alkanols or alkanol polymers ((alkanol)n). νCdbnd O of the latter indicated minor red shift and less variability compared to the former. An assumption was made and validated about the sequestering of hydroxyl group by the bulky hydrophobic chain in (alkanol)n, creating what we refer to as "screening effects". Ab initio calculation, on the other hand, provided insights for possible hydrogen binding between DMP and (ethanol)n or between ethanol monomers. The two components of Band I observed in inert solvents were assigned to the two Cdbnd O groups adopting differentiated conformations. This in turn prompted our consideration that hydrogen binding was highly selective in favor of lowly associated (alkanol)n and the particular Cdbnd O group having relatively less steric hindrance and stronger electron-donating capacity. Band II was therefore believed to derive from hydrogen-bond interactions mainly in manner of 1:1 and 1:2 DMP-(alkanol)n complexes.

Nuclear magnetic resonance shielding constants and chemical shifts in linear 199Hg compounds: a comparison of three relativistic computational methods.

PubMed

Arcisauskaite, Vaida; Melo, Juan I; Hemmingsen, Lars; Sauer, Stephan P A

2011-07-28

We investigate the importance of relativistic effects on NMR shielding constants and chemical shifts of linear HgL(2) (L = Cl, Br, I, CH(3)) compounds using three different relativistic methods: the fully relativistic four-component approach and the two-component approximations, linear response elimination of small component (LR-ESC) and zeroth-order regular approximation (ZORA). LR-ESC reproduces successfully the four-component results for the C shielding constant in Hg(CH(3))(2) within 6 ppm, but fails to reproduce the Hg shielding constants and chemical shifts. The latter is mainly due to an underestimation of the change in spin-orbit contribution. Even though ZORA underestimates the absolute Hg NMR shielding constants by ∼2100 ppm, the differences between Hg chemical shift values obtained using ZORA and the four-component approach without spin-density contribution to the exchange-correlation (XC) kernel are less than 60 ppm for all compounds using three different functionals, BP86, B3LYP, and PBE0. However, larger deviations (up to 366 ppm) occur for Hg chemical shifts in HgBr(2) and HgI(2) when ZORA results are compared with four-component calculations with non-collinear spin-density contribution to the XC kernel. For the ZORA calculations it is necessary to use large basis sets (QZ4P) and the TZ2P basis set may give errors of ∼500 ppm for the Hg chemical shifts, despite deceivingly good agreement with experimental data. A Gaussian nucleus model for the Coulomb potential reduces the Hg shielding constants by ∼100-500 ppm and the Hg chemical shifts by 1-143 ppm compared to the point nucleus model depending on the atomic number Z of the coordinating atom and the level of theory. The effect on the shielding constants of the lighter nuclei (C, Cl, Br, I) is, however, negligible. © 2011 American Institute of Physics

GW/Bethe-Salpeter calculations for charged and model systems from real-space DFT

NASA Astrophysics Data System (ADS)

Strubbe, David A.

GW and Bethe-Salpeter (GW/BSE) calculations use mean-field input from density-functional theory (DFT) calculations to compute excited states of a condensed-matter system. Many parts of a GW/BSE calculation are efficiently performed in a plane-wave basis, and extensive effort has gone into optimizing and parallelizing plane-wave GW/BSE codes for large-scale computations. Most straightforwardly, plane-wave DFT can be used as a starting point, but real-space DFT is also an attractive starting point: it is systematically convergeable like plane waves, can take advantage of efficient domain parallelization for large systems, and is well suited physically for finite and especially charged systems. The flexibility of a real-space grid also allows convenient calculations on non-atomic model systems. I will discuss the interfacing of a real-space (TD)DFT code (Octopus, www.tddft.org/programs/octopus) with a plane-wave GW/BSE code (BerkeleyGW, www.berkeleygw.org), consider performance issues and accuracy, and present some applications to simple and paradigmatic systems that illuminate fundamental properties of these approximations in many-body perturbation theory.

SU-C-204-03: DFT Calculations of the Stability of DOTA-Based-Radiopharmaceuticals

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

Khabibullin, A.R.; Woods, L.M.; Karolak, A.

2016-06-15

Purpose: Application of the density function theory (DFT) to investigate the structural stability of complexes applied in cancer therapy consisting of the 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelated to Ac225, Fr221, At217, Bi213, and Gd68 radio-nuclei. Methods: The possibility to deliver a toxic payload directly to tumor cells is a highly desirable aim in targeted alpha particle therapy. The estimation of bond stability between radioactive atoms and the DOTA chelating agent is the key element in understanding the foundations of this delivery process. Thus, we adapted the Vienna Ab-initio Simulation Package (VASP) with the projector-augmented wave method and a plane-wave basis setmore » in order to study the stability and electronic properties of DOTA ligand chelated to radioactive isotopes. In order to count for the relativistic effect of radioactive isotopes we included Spin-Orbit Coupling (SOC) in the DFT calculations. Five DOTA complex structures were represented as unit cells, each containing 58 atoms. The energy optimization was performed for all structures prior to calculations of electronic properties. Binding energies, electron localization functions as well as bond lengths between atoms were estimated. Results: Calculated binding energies for DOTA-radioactive atom systems were −17.792, −5.784, −8.872, −13.305, −18.467 eV for Ac, Fr, At, Bi and Gd complexes respectively. The displacements of isotopes in DOTA cages were estimated from the variations in bond lengths, which were within 2.32–3.75 angstroms. The detailed representation of chemical bonding in all complexes was obtained with the Electron Localization Function (ELF). Conclusion: DOTA-Gd, DOTA-Ac and DOTA-Bi were the most stable structures in the group. Inclusion of SOC had a significant role in the improvement of DFT calculation accuracy for heavy radioactive atoms. Our approach is found to be proper for the investigation of structures with DOTA

ERBB3: A potential serum biomarker for early detection and therapeutic target for devil facial tumour 1 (DFT1)

PubMed Central

Kunde, Dale A.; Taylor, Robyn L.; Pyecroft, Stephen B.; Sohal, Sukhwinder Singh; Snow, Elizabeth T.

2017-01-01

Devil Facial Tumour 1 (DFT1) is one of two transmissible neoplasms of Tasmanian devils (Sarcophilus harrisii) predominantly affecting their facial regions. DFT1’s cellular origin is that of Schwann cell lineage where lesions are evident macroscopically late in the disease. Conversely, the pre-clinical timeframe from cellular transmission to appearance of DFT1 remains uncertain demonstrating the importance of an effective pre-clinical biomarker. We show that ERBB3, a marker expressed normally by the developing neural crest and Schwann cells, is immunohistohemically expressed by DFT1, therefore the potential of ERBB3 as a biomarker was explored. Under the hypothesis that serum ERBB3 levels may increase as DFT1 invades local and distant tissues our pilot study determined serum ERBB3 levels in normal Tasmanian devils and Tasmanian devils with DFT1. Compared to the baseline serum ERBB3 levels in unaffected Tasmanian devils, Tasmanian devils with DFT1 showed significant elevation of serum ERBB3 levels. Interestingly Tasmanian devils with cutaneous lymphoma (CL) also showed elevation of serum ERBB3 levels when compared to the baseline serum levels of Tasmanian devils without DFT1. Thus, elevated serum ERBB3 levels in otherwise healthy looking devils could predict possible DFT1 or CL in captive or wild devil populations and would have implications on the management, welfare and survival of Tasmanian devils. ERBB3 is also a therapeutic target and therefore the potential exists to consider modes of administration that may eradicate DFT1 from the wild. PMID:28591206

A VLSI pipeline design of a fast prime factor DFT on a finite field

NASA Technical Reports Server (NTRS)

Truong, T. K.; Hsu, I. S.; Shao, H. M.; Reed, I. S.; Shyu, H. C.

1986-01-01

A conventional prime factor discrete Fourier transform (DFT) algorithm is used to realize a discrete Fourier-like transform on the finite field, GF(q sub n). A pipeline structure is used to implement this prime factor DFT over GF(q sub n). This algorithm is developed to compute cyclic convolutions of complex numbers and to decode Reed-Solomon codes. Such a pipeline fast prime factor DFT algorithm over GF(q sub n) is regular, simple, expandable, and naturally suitable for VLSI implementation. An example illustrating the pipeline aspect of a 30-point transform over GF(q sub n) is presented.

DFT Study of Optical Properties of Pt-based Complexes

NASA Astrophysics Data System (ADS)

Oprea, Corneliu I.; Dumbravǎ, Anca; Moscalu, Florin; Nicolaides, Atnanassios; Gîrţu, Mihai A.

2010-01-01

We report Density Functional Theory (DFT) calculations providing the geometrical and electronic structures, as well as the vibrational and optical properties of the homologous series of Pt-pyramidalized olefin complexes (CH2)n-(C8H10)Pt(PH3)2, where n = 0, 1, and 2, in their neutral and oxidized states. All complexes were geometry optimized for the singlet ground state in vacuum using DFT methods with B3LYP exchange-correlation functional and the Effective Core Potential LANL2DZ basis set, within the frame of Gaussian03 quantum chemistry package. We find the coordination geometry of Pt to be distorted square planar, with dihedral angles ranging from 0°, for n = 0 and 1, which have C2V symmetry to 3.4°, for n = 2 with C2 symmetry. The Mulliken charge analysis allows a discussion of the oxidation state of the Pt ion. Electronic transitions were calculated at the same level of theory by means of Time Dependant-DFT. For n = 2 the electronic absorption bands are located in the UV region of the spectrum, the transitions being assigned to metal to ligand charge transfers. The relevance of these Pt-based compounds as possible pigments for dye-sensitized solar cells is discussed.

Adaptive DFT-Based Interferometer Fringe Tracking

NASA Astrophysics Data System (ADS)

Wilson, Edward; Pedretti, Ettore; Bregman, Jesse; Mah, Robert W.; Traub, Wesley A.

2005-12-01

An automatic interferometer fringe tracking system has been developed, implemented, and tested at the Infrared Optical Telescope Array (IOTA) Observatory at Mount Hopkins, Arizona. The system can minimize the optical path differences (OPDs) for all three baselines of the Michelson stellar interferometer at IOTA. Based on sliding window discrete Fourier-transform (DFT) calculations that were optimized for computational efficiency and robustness to atmospheric disturbances, the algorithm has also been tested extensively on offline data. Implemented in ANSI C on the 266 MHz PowerPC processor running the VxWorks real-time operating system, the algorithm runs in approximately [InlineEquation not available: see fulltext.] milliseconds per scan (including all three interferograms), using the science camera and piezo scanners to measure and correct the OPDs. The adaptive DFT-based tracking algorithm should be applicable to other systems where there is a need to detect or track a signal with an approximately constant-frequency carrier pulse. One example of such an application might be to the field of thin-film measurement by ellipsometry, using a broadband light source and a Fourier-transform spectrometer to detect the resulting fringe patterns.

Comparative study of DFT+U functionals for non-collinear magnetism

NASA Astrophysics Data System (ADS)

Ryee, Siheon; Han, Myung Joon

2018-07-01

We performed comparative analysis for DFT+U functionals to better understand their applicability to non-collinear magnetism. Taking LiNiPO4 and Sr2IrO4 as examples, we investigated the results out of two formalisms based on charge-only density and spin density functional plus U calculations. Our results show that the ground state spin order in terms of tilting angle is strongly dependent on Hund J. In particular, the opposite behavior of canting angles as a function of J is found for LiNiPO4. The dependence on the other physical parameters such as Hubbard U and Slater parameterization is investigated. We also discuss the formal aspects of these functional dependences as well as parameter dependences. The current study provides useful information and important intuition for the first-principles calculation of non-collinear magnetic materials.

Chemisorption of Hydroxide on 2D Materials from DFT Calculations: Graphene versus Hexagonal Boron Nitride.

PubMed

Grosjean, Benoit; Pean, Clarisse; Siria, Alessandro; Bocquet, Lydéric; Vuilleumier, Rodolphe; Bocquet, Marie-Laure

2016-11-17

Recent nanofluidic experiments revealed strongly different surface charge measurements for boron-nitride (BN) and graphitic nanotubes when in contact with saline and alkaline water (Nature 2013, 494, 455-458; Phys. Rev. Lett. 2016, 116, 154501). These observations contrast with the similar reactivity of a graphene layer and its BN counterpart, using density functional theory (DFT) framework, for intact and dissociative adsorption of gaseous water molecules. Here we investigate, by DFT in implicit water, single and multiple adsorption of anionic hydroxide on single layers. A differential adsorption strength is found in vacuum for the first ionic adsorption on the two materials-chemisorbed on BN while physisorbed on graphene. The effect of implicit solvation reduces all adsorption values, resulting in a favorable (nonfavorable) adsorption on BN (graphene). We also calculate a pK a ≃ 6 for BN in water, in good agreement with experiments. Comparatively, the unfavorable results for graphene in water echo the weaker surface charge measurements but point to an alternative scenario.

Chemisorption of Hydroxide on 2D Materials From DFT Calculations: Graphene Versus Hexagonal Boron Nitride

PubMed Central

Grosjean, Benoit; Pean, Clarisse; Siria, Alessandro; Bocquet, Lyderic; Vuilleumier, Rodolphe; Bocquet, Marie-Laure

2017-01-01

Recent nanofluidic measurements revealed strongly different surface charge measurements for boron-nitride and graphitic nanotubes when in contact with saline and alkaline water. 1,2 These observations contrast with the similar reactivity of a graphene layer and its boron nitride counterpart, using Density Functional Theory (DFT) framework, for intact and dissociative adsorption of gaseous water molecules. Here, we investigate, by DFT in implicit water, single and multiple adsorption of anionic hydroxide on single layers. A differential adsorption strength is found in vacuum for the first ionic adsorption on the two materials – chemisorbed on BN while physisorbed on graphene. The effect of implicit solvation reduces all adsorption values resulting in a favorable (non-favorable) adsorption on BN (graphene). We also calculate a pKa ≃ 6 for BN in water, in good agreement with experiments. Comparatively, the unfavorable results for graphene in water echoes the weaker surface charge measurements, but points to an alternative scenario. PMID:27809540

SeO2 adsorption on CaO surface: DFT and experimental study on the adsorption of multiple SeO2 molecules

NASA Astrophysics Data System (ADS)

Fan, Yaming; Zhuo, Yuqun; Li, Liangliang

2017-10-01

SeO2 adsorption mechanisms on CaO surface were firstly investigated by both density functional theory (DFT) calculations and adsorption experiments. Adsorption of multiple SeO2 on the CaO (001) surface was investigated using slab model. Based on the results of adsorption energy and surface property, a double-layer adsorption mechanisms were proposed. In experiments, the SeO2 adsorption products were prepared in a U-shaped quartz reactor at 200 °C. The surface morphology was investigated by field emission scanning electron microscopy (FE-SEM). The superficial and total SeO2 mass fractions were measured by X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively. The surface valence state and bulk structure are determined by XPS and X-Ray Diffraction (XRD). The experimental results are in good agreement with the DFT results. In conclusion, the fundamental SeO2 chemisorption mechanisms on CaO surface were suggested.

Modeling Excited States in TiO2 Nanoparticles: On the Accuracy of a TD-DFT Based Description

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

Berardo, Enrico; Hu, Hanshi; Shevlin, S. A.

2014-03-11

We have investigated the suitability of Time-Dependent Density Functional Theory (TD-DFT) to describe vertical low-energy excitations in naked and hydrated titanium dioxide nanoparticles through a comparison with results from Equation-of-Motion Coupled Cluster (EOM-CC) quantum chemistry methods. We demonstrate that for most TiO2 nanoparticles TD-DFT calculations with commonly used exchange-correlation (XC-)potentials (e.g. B3LYP) and EOM-CC methods give qualitatively similar results. Importantly, however, we also show that for an important subset of structures, TD-DFT gives qualitatively different results depending upon the XC-potential used and that in this case only TD-CAM-B3LYP and TD-BHLYP calculations yield results that are consistent with those obtained usingmore » EOM-CC theory. Moreover, we demonstrate that the discrepancies for such structures arise from a particular combination of defects, excitations involving which are charge-transfer excitations and hence are poorly described by XC-potentials that contain no or low fractions of Hartree-Fock like exchange. Finally, we discuss that such defects are readily healed in the presence of ubiquitously present water and that as a result the description of vertical low-energy excitations for hydrated TiO2 nanoparticles is hence non-problematic.« less

Conformational, electronic, and spectroscopic characterization of isophthalic acid (monomer and dimer structures) experimentally and by DFT

NASA Astrophysics Data System (ADS)

Bardak, F.; Karaca, C.; Bilgili, S.; Atac, A.; Mavis, T.; Asiri, A. M.; Karabacak, M.; Kose, E.

2016-08-01

Isophthalic acid (C6H4(CO2H)2) is a noteworthy organic compound widely used in coating and synthesis of resins and the production of commercially important polymers such as drink plastic bottles. The effects of isophthalic acid (IPA) on human health, toxicology, and biodegradability are the main focus of many researchers. Because structural and spectroscopic investigation of molecules provides a deep understanding of interactional behaviors of compounds, this study stands for exploring those features. Therefore, the spectroscopic, structural, electronic, and thermodynamical properties of IPA were thoroughly studied in this work experimentally using UV-Vis, 1H and 13C NMR, FT-IR, FT-Raman and theoretically via DFT and TD-DFT calculations. The UV-Vis absorption spectrum in water was taken in the region 200-400 nm. The NMR chemical shifts (1H and 13C) were recorded in DMSO solution. The infrared and Raman spectra of the solid IPA were recorded in the range of 4000-400 cm- 1 and 3500-50 cm- 1, respectively. DFT and TD-DFT calculations were performed at the level of B3LYP/6-311++G(d,p) in determination of geometrical structure, electronic structure analysis and normal mode. The 13C and 1H nuclear magnetic resonance (NMR) spectra were estimated by using the gauge-invariant atomic orbital (GIAO) method. The scaled quantum mechanics (SQM) method was used to determine the total energy distribution (TED) to assign the vibrational modes accurately. Weak interactions such as hydrogen bonding and Van der Walls were analyzed via reduced density gradient (RDG) analysis in monomeric and dimeric forms. Furthermore, the excitation energies, density of state (DOS) diagram, thermodynamical properties, molecular electro-static potential (MEP), and nonlinear optical (NLO) properties were obtained.

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.

TD-DFT Insight into Photodissociation of Co-C Bond in Coenzyme B12

NASA Astrophysics Data System (ADS)

Kozlowski, Pawel; Liu, Hui; Kornobis, Karina; Lodowski, Piotr; Jaworska, Maria

2013-12-01

Coenzyme B12 (AdoCbl) is one of the most biologically active forms of vitamin B12, and continues to be a topic of active research interest. The mechanism of Co-C bond cleavage in AdoCbl, and the corresponding enzymatic reactions are however, not well understood at the molecular level. In this work, time-dependent density functional theory (TD-DFT) has been applied to investigate the photodissociation of coenzyme B12. To reduce computational cost, while retaining the major spectroscopic features of AdoCbl, a truncated model based on ribosylcobalamin (RibCbl) was used to simulate Co-C photodissociation. Equilibrium geometries of RibCbl were obtained by optimization at the DFT/BP86/TZVP level of theory, and low-lying excited states were calculated by TD-DFT using the same functional and basis set. The calculated singlet states, and absorption spectra were simulated in both the gas phase, and water, using the polarizable continuum model (PCM). Both spectra were in reasonable agreement with experimental data, and potential energy curves based on vertical excitations were plotted to explore the nature of Co-C bond dissociation. It was found that a repulsive 3(σCo-C → σ*Co-C) triplet state became dissociative at large Co-C bond distance, similar to a previous observation for methylcobalamin (MeCbl). Furthermore, potential energy surfaces (PESs) obtained as a function of both Co-CRib and Co-NIm distances, identify the S1 state as a key intermediate generated during photoexcitation of RibCbl, attributed to a mixture of a MLCT (metal-to-ligand charge transfer) and a σ bonding-ligand charge transfer (SBLCT) states.

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.

Error compensation of IQ modulator using two-dimensional DFT

NASA Astrophysics Data System (ADS)

Ohshima, Takashi; Maesaka, Hirokazu; Matsubara, Shinichi; Otake, Yuji

2016-06-01

It is important to precisely set and keep the phase and amplitude of an rf signal in the accelerating cavity of modern accelerators, such as an X-ray Free Electron Laser (XFEL) linac. In these accelerators an acceleration rf signal is generated or detected by an In-phase and Quadrature (IQ) modulator, or a demodulator. If there are any deviations of the phase and the amplitude from the ideal values, crosstalk between the phase and the amplitude of the output signal of the IQ modulator or the demodulator arises. This causes instability of the feedback controls that simultaneously stabilize both the rf phase and the amplitude. To compensate for such deviations, we developed a novel compensation method using a two-dimensional Discrete Fourier Transform (DFT). Because the observed deviations of the phase and amplitude of an IQ modulator involve sinusoidal and polynomial behaviors on the phase angle and the amplitude of the rf vector, respectively, the DFT calculation with these basis functions makes a good approximation with a small number of compensation coefficients. Also, we can suppress high-frequency noise components arising when we measure the deviation data. These characteristics have advantages compared to a Look Up Table (LUT) compensation method. The LUT method usually demands many compensation elements, such as about 300, that are not easy to treat. We applied the DFT compensation method to the output rf signal of a C-band IQ modulator at SACLA, which is an XFEL facility in Japan. The amplitude deviation of the IQ modulator after the DFT compensation was reduced from 15.0% at the peak to less than 0.2% at the peak for an amplitude control range of from 0.1 V to 0.9 V (1.0 V full scale) and for a phase control range from 0 degree to 360 degrees. The number of compensation coefficients is 60, which is smaller than that of the LUT method, and is easy to treat and maintain.

Synthesis, FTIR, FT-Raman, UV-visible, ab initio and DFT studies on benzohydrazide.

PubMed

Arjunan, V; Rani, T; Mythili, C V; Mohan, S

2011-08-01

A systematic vibrational spectroscopic assignment and analysis of benzohydrazide (BH) has been carried out by using FTIR and FT-Raman spectral data. The vibrational analysis were aided by electronic structure calculations--ab initio (RHF) and hybrid density functional methods (B3LYP and B3PW91) performed with 6-31G(d,p) and 6-311++G(d,p) basis sets. Molecular equilibrium geometries, electronic energies, IR intensities, harmonic vibrational frequencies, depolarization ratios and Raman activities have been computed. Potential energy distribution (PED) and normal mode analysis have also been performed. The assignments proposed based on the experimental IR and Raman spectra have been reviewed and complete assignment of the observed spectra have been proposed. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and λ(max) were determined by time-dependent DFT (TD-DFT) method. The geometrical, thermodynamical parameters and absorption wavelengths were compared with the experimental data. The interactions of carbonyl and hydrazide groups on the benzene ring skeletal modes were investigated. Copyright © 2011 Elsevier B.V. All rights reserved.

Supramolecular architecture of 5-bromo-7-methoxy-1-methyl-1H-benzoimidazole.3H2O: Synthesis, spectroscopic investigations, DFT computation, MD simulations and docking studies

NASA Astrophysics Data System (ADS)

Murthy, P. Krishna; Smitha, M.; Sheena Mary, Y.; Armaković, Stevan; Armaković, Sanja J.; Rao, R. Sreenivasa; Suchetan, P. A.; Giri, L.; Pavithran, Rani; Van Alsenoy, C.

2017-12-01

Crystal and molecular structure of newly synthesized compound 5-bromo-7-methoxy-1-methyl-1H-benzoimidazole (BMMBI) has been authenticated by single crystal X-ray diffraction, FT-IR, FT-Raman, 1H NMR, 13C NMR and UV-Visible spectroscopic techniques; compile both experimental and theoretical results which are performed by DFT/B3LYP/6-311++G(d,p) method at ground state in gas phase. Visualize nature and type of intermolecular interactions and crucial role of these interactions in supra-molecular architecture has been investigated by use of a set of graphical tools 3D-Hirshfeld surfaces and 2D-fingerprint plots analysis. The title compound stabilized by strong intermolecular hydrogen bonds N⋯Hsbnd O and O⋯Hsbnd O, which are envisaged by dark red spots on dnorm mapped surfaces and weak Br⋯Br contacts envisaged by red spot on dnorm mapped surface. The detailed fundamental vibrational assignments of wavenumbers were aid by with help of Potential Energy distribution (PED) analysis by using GAR2PED program and shows good agreement with experimental values. Besides frontier orbitals analysis, global reactivity descriptors, natural bond orbitals and Mullikan charges analysis were performed by same basic set at ground state in gas phase. Potential reactive sites of the title compound have been identified by ALIE, Fukui functions and MEP, which are mapped to the electron density surfaces. Stability of BMMBI have been investigated from autoxidation process and pronounced interaction with water (hydrolysis) by using bond dissociation energies (BDE) and radial distribution functions (RDF), respectively after MD simulations. In order to identify molecule's most important reactive spots we have used a combination of DFT calculations and MD simulations. Reactivity study encompassed calculations of a set of quantities such as: HOMO-LUMO gap, MEP and ALIE surfaces, Fukui functions, bond dissociation energies and radial distribution functions. To confirm the potential

Solid-state (185/187)Re NMR and GIPAW DFT study of perrhenates and Re2(CO)10: chemical shift anisotropy, NMR crystallography, and a metal-metal bond.

PubMed

Widdifield, Cory M; Perras, Frédéric A; Bryce, David L

2015-04-21

provided for NH4ReO4, NaReO4 and RbReO4. These calculations are able to reproduce many of the experimental trends in rhenium δiso values and EFG tensor magnitudes. Using KReO4 as a prototypical perrhenate-containing system, we establish a correlation between the tetrahedral shear strain parameter (|ψ|) and the nuclear electric quadrupolar coupling constant (CQ), which enables the refinement of the structure of ND4ReO4. Shortcomings in traditional DFT approaches, even when including relativistic effects via the zeroth-order regular approximation (ZORA), for calculating rhenium NMR tensor parameters are identified for Re2(CO)10.

Structural, vibrational and nuclear magnetic resonance investigations of 4-bromoisoquinoline by experimental and theoretical DFT methods.

PubMed

Arjunan, V; Thillai Govindaraja, S; Jayapraksh, A; Mohan, S

2013-04-15

Quantum chemical calculations of energy, structural parameters and vibrational wavenumbers of 4-bromoisoquinoline (4BIQ) were carried out by using B3LYP method using 6-311++G(**), cc-pVTZ and LANL2DZ basis sets. The optimised geometrical parameters obtained by DFT calculations are in good agreement with electron diffraction data. Interpretations of the experimental FTIR and FT-Raman spectra have been reported with the aid of the theoretical wavenumbers. The differences between the observed and scaled wavenumber values of most of the fundamentals are very small. The thermodynamic parameters have also been computed. Electronic properties of the molecule were discussed through the molecular electrostatic potential surface, HOMO-LUMO energy gap and NBO analysis. To provide precise assignments of (1)H and (13)CNMR spectra, isotropic shielding and chemical shifts were calculated with the Gauge-Invariant Atomic Orbital (GIAO) method. Copyright © 2013 Elsevier B.V. All rights reserved.

Application of DFT Filter Banks and Cosine Modulated Filter Banks in Filtering

NASA Technical Reports Server (NTRS)

Lin, Yuan-Pei; Vaidyanathan, P. P.

1994-01-01

None given. This is a proposal for a paper to be presented at APCCAS '94 in Taipei, Taiwan. (From outline): This work is organized as follows: Sec. II is devoted to the construction of the new 2m channel under-decimated DFT filter bank. Implementation and complexity of this DFT filter bank are discussed therein. IN a similar manner, the new 2m channel cosine modulated filter bank is discussed in Sec. III. Design examples are given in Sec. IV.

Benchmarks and Reliable DFT Results for Spin Gaps of Small Ligand Fe(II) Complexes

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

Song, Suhwan; Kim, Min-Cheol; Sim, Eunji

2017-05-01

All-electron fixed-node diffusion Monte Carlo provides benchmark spin gaps for four Fe(II) octahedral complexes. Standard quantum chemical methods (semilocal DFT and CCSD(T)) fail badly for the energy difference between their high- and low-spin states. Density-corrected DFT is both significantly more accurate and reliable and yields a consistent prediction for the Fe-Porphyrin complex

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.

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.

Understanding Density Functional Theory (DFT) and Completing it in Practice

NASA Astrophysics Data System (ADS)

Bagayoko, Diola

2015-03-01

A brief review of the seminal article by Hohenberg and Kohn leads to two conditions that have to be met by electronic structure calculations in order for their results to represent the physics content of DFT. One of these conditions is often the verifiable attainment of the absolute minima of the occupied energies. Using the second Hohenberg Kohn theorem, we show that results of calculations that do not meet this condition, when it applies, do not necessarily represent DFT findings. We illustrate this fact with over 100 calculated band gaps that are much smaller than corresponding, measured ones; in contrast, we list calculations that strictly adhered to the aforementioned conditions and whose results are in excellent agreement with experiment. We describe two crucial steps in the latter calculations that add to or complete DFT in practice. Some implications of our findings for academia, industry, and program package developers will be discussed. Acknowledgments: This work was funded in part by the National Science Foundation (NSF) and the Louisiana Board of Regents, through LASiGMA [Award Nos. EPS- 1003897, NSF (2010-15)-RII-SUBR] and NSF HRD-1002541, the US Department of Energy - National, Nuclear Security Administration (NNSA) (Award Nos. DE-NA0001861 and DE- NA0002630), LaSPACE, and LONI-SUBR.

Ab initio DFT+U study of He atom incorporation into UO(2) crystals.

PubMed

Gryaznov, Denis; Heifets, Eugene; Kotomin, Eugene

2009-09-07

We present and discuss results of the density functional theory (DFT) for perfect UO(2) crystals with He atoms in octahedral interstitial positions therein. We have calculated basic bulk crystal properties and He incorporation energies into the low temperature anti-ferromagnetic UO(2) phase using several exchange-correlation functionals within the spin-polarized local density (LDA) and generalized gradient (GGA) approximations. In all DFT calculations we included the on-site correlation corrections using the Hubbard model (DFT+U approach). We analysed a potential crystalline symmetry reduction from tetragonal down to orthorhombic structure and confirmed the presence of the Jahn-Teller effect in a perfect UO(2). We discuss also the problem of a conducting electronic state arising when He is placed into a tetragonal antiferromagnetic phase of UO(2) commonly used in defect modelling. Consequently, we found a specific monoclinic lattice distortion which allowed us to restore the semiconducting state and properly estimate He incorporation energies. Unlike the bulk properties, the He incorporation energy strongly depends on several factors, including the supercell size, the use of spin polarization, the exchange-correlation functionals and on-site correlation corrections. We compare our results for the He incorporation with the previous shell model and ab initio DFT calculations.

DFT studies of hydrocarbon combustion on metal surfaces.

PubMed

Arya, Mina; Mirzaei, Ali Akbar; Davarpanah, Abdol Mahmood; Barakati, Seyed Masoud; Atashi, Hossein; Mohsenzadeh, Abas; Bolton, Kim

2018-02-02

Catalytic combustion of hydrocarbons is an important technology to produce energy. Compared to conventional flame combustion, the catalyst enables this process to operate at lower temperatures; hence, reducing the energy required for efficient combustion. The reaction and activation energies of direct combustion of hydrocarbons (CH → C + H) on a series of metal surfaces were investigated using density functional theory (DFT). The data obtained for the Ag, Au, Al, Cu, Rh, Pt, and Pd surfaces were used to investigate the validity of the Brønsted-Evans-Polanyi (BEP) and transition state scaling (TSS) relations for this reaction on these surfaces. These relations were found to be valid (R 2  = 0.94 for the BEP correlation and R 2  = 1.0 for the TSS correlation) and were therefore used to estimate the energetics of the combustion reaction on Ni, Co, and Fe surfaces. It was found that the estimated transition state and activation energies (E TS  = -69.70 eV and E a  = 1.20 eV for Ni, E TS  = -87.93 eV and E a  = 1.08 eV for Co and E TS  = -92.45 eV and E a  = 0.83 eV for Fe) are in agreement with those obtained by DFT calculations (E TS  = -69.98 eV and E a  = 1.23 eV for Ni, E TS  = -87.88 eV and E a  = 1.08 eV for Co and E TS  = -92.57 eV and E a  = 0.79 eV for Fe). Therefore, these relations can be used to predict energetics of this reaction on these surfaces without doing the time consuming transition state calculations. Also, the calculations show that the activation barrier for CH dissociation decreases in the order Ag ˃ Au ˃ Al ˃ Cu ˃ Pt ˃ Pd ˃ Ni > Co > Rh > Fe.

Insufficient Hartree–Fock Exchange in Hybrid DFT Functionals Produces Bent Alkynyl Radical Structures

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

Oyeyemi, Victor B.; Keith, John A.; Pavone, Michele

2012-01-11

Density functional theory (DFT) is often used to determine the electronic and geometric structures of molecules. While studying alkynyl radicals, we discovered that DFT exchange-correlation (XC) functionals containing less than ~22% Hartree–Fock (HF) exchange led to qualitatively different structures than those predicted from ab initio HF and post-HF calculations or DFT XCs containing 25% or more HF exchange. We attribute this discrepancy to rehybridization at the radical center due to electron delocalization across the triple bonds of the alkynyl groups, which itself is an artifact of self-interaction and delocalization errors. Inclusion of sufficient exact exchange reduces these errors and suppressesmore » this erroneous delocalization; we find that a threshold amount is needed for accurate structure determinations. Finally, below this threshold, significant errors in predicted alkyne thermochemistry emerge as a consequence.« less

Effective empirical corrections for basis set superposition error in the def2-SVPD basis: gCP and DFT-C

NASA Astrophysics Data System (ADS)

Witte, Jonathon; Neaton, Jeffrey B.; Head-Gordon, Martin

2017-06-01

With the aim of mitigating the basis set error in density functional theory (DFT) calculations employing local basis sets, we herein develop two empirical corrections for basis set superposition error (BSSE) in the def2-SVPD basis, a basis which—when stripped of BSSE—is capable of providing near-complete-basis DFT results for non-covalent interactions. Specifically, we adapt the existing pairwise geometrical counterpoise (gCP) approach to the def2-SVPD basis, and we develop a beyond-pairwise approach, DFT-C, which we parameterize across a small set of intermolecular interactions. Both gCP and DFT-C are evaluated against the traditional Boys-Bernardi counterpoise correction across a set of 3402 non-covalent binding energies and isomerization energies. We find that the DFT-C method represents a significant improvement over gCP, particularly for non-covalently-interacting molecular clusters. Moreover, DFT-C is transferable among density functionals and can be combined with existing functionals—such as B97M-V—to recover large-basis results at a fraction of the cost.

DFT modeling of chemistry on the Z machine

NASA Astrophysics Data System (ADS)

Mattsson, Thomas

2013-06-01

Density Functional Theory (DFT) has proven remarkably accurate in predicting properties of matter under shock compression for a wide-range of elements and compounds: from hydrogen to xenon via water. Materials where chemistry plays a role are of particular interest for many applications. For example the deep interiors of Neptune, Uranus, and hundreds of similar exoplanets are composed of molecular ices of carbon, hydrogen, oxygen, and nitrogen at pressures of several hundred GPa and temperatures of many thousand Kelvin. High-quality thermophysical experimental data and high-fidelity simulations including chemical reaction are necessary to constrain planetary models over a large range of conditions. As examples of where chemical reactions are important, and demonstration of the high fidelity possible for these both structurally and chemically complex systems, we will discuss shock- and re-shock of liquid carbon dioxide (CO2) in the range 100 to 800 GPa, shock compression of the hydrocarbon polymers polyethylene (PE) and poly(4-methyl-1-pentene) (PMP), and finally simulations of shock compression of glow discharge polymer (GDP) including the effects of doping with germanium. Experimental results from Sandia's Z machine have time and again validated the DFT simulations at extreme conditions and the combination of experiment and DFT provide reliable data for evaluating existing and constructing future wide-range equations of state models for molecular compounds like CO2 and polymers like PE, PMP, and GDP. 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.

Appropriate description of intermolecular interactions in the methane hydrates: an assessment of DFT methods.

PubMed

Liu, Yuan; Zhao, Jijun; Li, Fengyu; Chen, Zhongfang

2013-01-15

Accurate description of hydrogen-bonding energies between water molecules and van der Waals interactions between guest molecules and host water cages is crucial for study of methane hydrates (MHs). Using high-level ab initio MP2 and CCSD(T) results as the reference, we carefully assessed the performance of a variety of exchange-correlation functionals and various basis sets in describing the noncovalent interactions in MH. The functionals under investigation include the conventional GGA, meta-GGA, and hybrid functionals (PBE, PW91, TPSS, TPSSh, B3LYP, and X3LYP), long-range corrected functionals (ωB97X, ωB97, LC-ωPBE, CAM-B3LYP, and LC-TPSS), the newly developed Minnesota class functionals (M06-L, M06-HF, M06, and M06-2X), and the dispersion-corrected density functional theory (DFT) (DFT-D) methods (B97-D, ωB97X-D, PBE-TS, PBE-Grimme, and PW91-OBS). We found that the conventional functionals are not suitable for MH, notably, the widely used B3LYP functional even predicts repulsive interaction between CH(4) and (H(2)O)(6) cluster. M06-2X is the best among the M06-Class functionals. The ωB97X-D outperforms the other DFT-D methods and is recommended for accurate first-principles calculations of MH. B97-D is also acceptable as a compromise of computational cost and precision. Considering both accuracy and efficiency, B97-D, ωB97X-D, and M06-2X functional with 6-311++G(2d,2p) basis set without basis set superposition error (BSSE) correction are recommended. Though a fairly large basis set (e.g., aug-cc-pVTZ) and BSSE correction are necessary for a reliable MP2 calculation, DFT methods are less sensitive to the basis set and BSSE correction if the basis set is sufficient (e.g., 6-311++G(2d,2p)). These assessments provide useful guidance for choosing appropriate methodology of first-principles simulation of MH and related systems. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.

DFT and ENDOR Study of Bixin Radical Cations and Neutral Radicals on Silica-Alumina.

PubMed

Tay-Agbozo, Sefadzi S; Krzyaniak, Matthew D; Bowman, Michael K; Street, Shane; Kispert, Lowell D

2015-06-18

Bixin, a carotenoid found in annatto (Bixa orellana), is unique among natural carotenoids by being water-soluble. We stabilized free radicals from bixin on the surface of silica-alumina (Si-Al) and characterized them by pulsed electron-nuclear double resonance (ENDOR). DFT calculations of unpaired electron spin distribution for various bixin radicals predict the EPR hyperfine couplings. Least-square fitting of experimental ENDOR spectra by spectra calculated from DFT hyperfine couplings characterized the radicals trapped on Si-Al. DFT predicts that the trans bixin radical cation is more stable than the cis bixin radical cation by 1.26 kcal/mol. This small energy difference is consistent with the 26% trans and 23% cis radical cations in the ENDOR spectrum. The remainder of the ENDOR spectrum is due to several neutral radicals formed by loss of a H(+) ion from the 9, 9', 13, or 13' methyl group, a common occurrence in all water-insoluble carotenoids previously studied. Although carboxyl groups of bixin strongly affect its solubility relative to other natural carotenoids, they do not alter properties of its free radicals based on DFT calculations and EPR measurements which remain similar to typical water-insoluble carotenoids.

Theoretical investigation of M@Pb122- and M@Sn122- Zintl clusters (M = Lrn+, Lun+, La3+, Ac3+ and n = 0, 1, 2, 3).

PubMed

Joshi, Meenakshi; Chandrasekar, Aditi; Ghanty, Tapan K

2018-06-06

The positions of lawrencium (Lr), lutetium (Lu), actinium (Ac) and lanthanum (La) in the periodic table have been a controversial topic for quite some time. According to studies carried out by different groups with their justifications, these elements may potentially be placed in the d-block, p-block or all four in a 15 element f-block. The present work looks into this issue from a new perspective, which involves encapsulation of these four elements into Zintl ion clusters, Pb122- and Sn122-, followed by the determination of the structural, thermodynamic and electronic properties of these endohedral M@Pb122- and M@Sn122- clusters (M = Lrn+, Lun+ with n = 0, 1, 2, 3) using first principles based density functional theory (DFT). These parameters are compared with similar clusters encapsulated La3+ and Ac3+ ions in order to seek out similarities and differences to draw conclusions about their placement in the periodic table. For the first time the structural, energetic, and electronic properties of these metal atom/ion encapsulated Pb122- and Sn122- clusters have been investigated thoroughly. Structural parameters such as bond distances, geometry and symmetry, electronic properties viz. the density of states, the molecular orbital ordering, the electron localization function, bond critical point properties and charge distributions have been analyzed. Additionally, the thermodynamic property of the binding energy during the encapsulation process has also been calculated. All M@Pb12+ and M@Sn12+ (M = Lr and Lu) clusters form stable 18 bonding electron magic number systems with shell closing. They show negative values of binding energy and relatively large HOMO-LUMO energy gaps indicating the stability of such clusters. All the calculated parameters for Lr encapsulated clusters closely match with the corresponding calculated parameters of Lu encapsulated clusters, confirming the similarity between Lr and Lu metal atoms in various oxidation states, though their atomic

DFT treatment of transport through Anderson junction: exact results and approximations

NASA Astrophysics Data System (ADS)

Burke, Kieron

2012-02-01

Since the pioneering break-junction experiments of Reed and Tour measuring the conductance of dithiolated benzene between gold leads, many researchers in physics and chemistry have been calculating conductance for such systems using density functional theory (DFT). Off resonance, the predicted current is often 10-100 times larger than that measured. This error is often ascribed to the application of ground-state DFT to a non-equilibrium problem. I will argue that, in fact, this is largely due to errors in the density functional approximations in popular use, rather than necessarily errors in the methodology. A stark illustration of this principle is the ability of DFT to reproduce the exact transmission through an Anderson junction at zero-temperature and weak bias, including the Kondo plateau, but only if the exact ground-state density functional is used. In fact, this case can be used to reverse-engineer the exact functional for this problem. Popular approximations can also be tested, including both smooth and discontinuous functionals of the density, as well as symmetry-broken approaches. [4pt] [1] Kondo effect given exactly by density functional theory, J. P. Bergfield, Z. Liu, K. Burke, and C. A. Stafford, arXiv:1106.3104; [0pt] [2] Broadening of the Derivative Discontinuity in Density Functional Theory, F. Evers, and P. Schmitteckert, arXiv:1106.3658; [0pt] [3] DFT-based transport calculations, Friedel's sum rule and the Kondo effect, P. Tr"oster, P. Schmitteckert, and F. Evers, arXiv:1106.3669; [0pt] [4] Towards a description of the Kondo effect using time-dependent density functional theory, G. Stefanucci, and S. Kurth, arXiv:1106.3728.

Synthesis and antibacterial activity of sulfonamides. SAR and DFT studies

NASA Astrophysics Data System (ADS)

Boufas, Wahida; Dupont, Nathalie; Berredjem, Malika; Berrezag, Kamel; Becheker, Imène; Berredjem, Hajira; Aouf, Nour-Eddine

2014-09-01

A series of substituted sulfonamide derivatives were synthesized from chlorosulfonyl isocyanate (CSI) in tree steps (carbamoylation, sulfamoylation and deprotection). Antibacterial activity in vitro of some newly formed compounds investigated against clinical strains Gram-positive and Gram-negative: Escherichia coli and Staphylococcus aureus applying the method of dilution and minimal inhibition concentration (MIC) methods. These compounds have significant bacteriostatic activity with totalities of bacterial strains used. DFT calculations with B3LYP/6-31G(d) level have been used to analyze the electronic and geometric characteristics deduced for the stable structure of three compounds presenting conjugation between a nitrogen atom N through its lone pair and an aromatic ring next to it. The principal quantum chemical descriptors have been correlated with the antibacterial activity.

Interaction of water with (silico)aluminophosphate zeotypes: a comparative investigation using dispersion-corrected DFT.

PubMed

Fischer, Michael

2016-06-21

Porous aluminophosphates (AlPOs) and silicoaluminophosphates (SAPOs) with zeolite-like structures have received considerable attention as potential adsorbents for heat transformation applications using water adsorption/desorption cycles. Since a detailed experimental characterisation of the water adsorption properties has only been performed for some of these materials, such as AlPO-18 (AEI topology) and SAPO-34 (CHA topology), more systematic insights regarding the influence of the pore topology and (for SAPOs) the arrangement of the framework protons on the affinity towards water are lacking. To study the relationships between structure and properties in more detail, the interaction of water with six structurally different AlPOs (with AEI, AFX, CHA, ERI, GIS, RHO topologies) and their SAPO analogues was investigated using dispersion-corrected density-functional theory (DFT-D) calculations. Different possible locations of silicon atoms and charge-balancing protons were considered for the SAPO systems. The calculations for SAPOs at low water loadings (one H2O molecule per framework proton) revealed that the interaction energies exhibit a considerable variation, ranging from -75 to -100 kJ mol(-1) (per water molecule). The differences in interaction energy were rationalised with the different structural environment of the framework protons at which the water molecules are adsorbed. At high water uptakes (near saturation), interaction energies in the range of -65 kJ mol(-1) were obtained for all AlPOs, and there was no evidence for a marked influence of pore size and/or topology on the interaction strength. The interaction of water with SAPOs was found to be approximately 5 kJ mol(-1) stronger than for AlPOs due to an increased contribution of electrostatic interactions. An analysis of the structural changes upon water adsorption revealed striking differences between the distinct topologies, with the materials with GIS and RHO topologies being distorted much more

First evidence for the production of OH radicals by carbonyl oxides in solution phase A DFT investigation

NASA Astrophysics Data System (ADS)

Cremer, Dieter; Kraka, Elfi; Sosa, Carlos

2001-03-01

Dimesitylketone O-oxide ( 1) rearranges in solution to yield the alcohol 2-methylhydroxy-pentamethylbenzophenone ( 5) and dimesitylketone ( 6). DFT-B3LYP/cc-pVTZ calculations reveal that H migration from an o-methyl group to the terminal O atom of the COO unit of 1 rather than the isomerization of 1 is energetically the most favorable process. Calculated activation enthalpies (gas phase: 12.8 kcal/mol; CH 3CN solution: 12.4 kcal/mol) are in excellent agreement with measured activation enthalpies (CFCl 3 solution: 13.2±0.2 kcal/mol; CH 3CN solution: 12.5±0.3 kcal/mol). The hydroperoxide formed by H migration decomposes to a OH and a benzyl radical. Recombination in the solvent cage leads to alcohol 5 while diffusion of OH out of the solvent cage yields 6.

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.

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.

The structure of N2 adsorbed on the rumpled NaCl(100) surface—A combined LEED and DFT-D study

NASA Astrophysics Data System (ADS)

Vogt, Jochen

2012-11-01

The structure of N2 physisorbed on the NaCl(100) single crystal surface is investigated by means of quantitative low-energy electron diffraction (LEED) in combination with dispersion corrected density functional theory (DFT-D). In the temperature range between 20 K and 45 K, a p(1 × 1) structure is observed in the LEED experiment. According to the structure analysis based on the measured diffraction spot intensity profiles, the N2 molecules are adsorbed over the topmost Na+ ions. The experimental distance of the lower nitrogen to the Na+ ion underneath is (2.55 ± 0.07) Å; the corresponding DFT-D value is 2.65 Å. The axes of the molecules are tilted (26 ± 3)° with respect to the surface normal, while in the zero Kelvin optimum structure from DFT-D, the molecules have a perpendicular orientation. The experimental monolayer heat of adsorption, deduced from a Fowler-Guggenheim kinetic model of adsorption is -(13.6 ± 1.6) kJ mol-1, including a lateral molecule-molecule interaction energy of -(2.0 ± 0.4) kJ mol-1. The zero Kelvin adsorption energy from DFT-D, including zero point energy correction, is -15.6 kJ mol-1; the molecule-molecule interaction is -2.4 kJ mol-1. While the rumpling of the NaCl(100) surface is unchanged upon adsorption of nitrogen, the best-fit root mean square thermal displacements of the ions in the topmost substrate layer are significantly reduced.

FT-Raman, FT-IR spectroscopic and DFT studies of hexaphenoxycyclotriphosphazene

NASA Astrophysics Data System (ADS)

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

2016-07-01

The FTIR and FT Raman measurements of zero Gc0‧ -H and first Gc1‧ -H generations of phosphorus dendrimer built from cyclotriphosphazene core with phenoxy and deuterophenoxy terminal groups have been performed. In order to evaluate how much the frequencies, shift when changing the electronics of the system the FTIR and FT Raman spectra of phosphorus‒containing dendron with five terminal oxybenzaldehyde and one ester function Gci‧ have been also studied. Structural optimization and normal mode analysis were obtained for Gc0‧ -H and Gc0‧ -D by the density functional theory (DFT). It is discovered that dendrimer molecule exists in a stable conformation with six phenoxy terminal groups spaced above and below the flat cyclotriphosphazene core. Optimized geometric bond length and angles obtained by DFT show good agreement with a previously-published X-ray study. The phenoxy terminal groups are characterized by the well-defined line at 993 cm-1 in the experimental Raman spectrum of Gc0‧ -H and by line at 960 cm-1 in the Raman spectrum of Gc0‧ -D. Relying on DFT calculations a complete vibrational assignment is proposed for the studied dendrimers. The frequencies and relative intensity of the bands at 1589, 1487 cm-1 in the IR spectra show marked difference in dependence of the substituents on the aromatic ring.

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.

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.

Why use DFT methods in the study of carbohydrates?

USDA-ARS?s Scientific Manuscript database

The recent advances in density functional theory (DFT) and computer technology allow us to study systems with more than 100 atoms routinely. This makes it feasible to study large carbohydrate molecules via quantum mechanical methods, whereas in the past, studies of carbohydrates were restricted to ...

Understanding the Relativistic Generalization of Density Functional Theory (DFT) and Completing it in Practice

NASA Astrophysics Data System (ADS)

Bagayoko, Diola

In 2014, 50 years following the introduction of density functional theory (DFT), a rigorous understanding of it was published [AIP Advances, 4, 127104 (2014)]. This understanding included necessary steps ab initio electronic structure calculations have to take if their results are to possess the full physical content of DFT. These steps guarantee the fulfillment of conditions of validity of DFT; not surprisingly, they have led to accurate descriptions of several dozens of semiconductors, from first principle, without invoking derivative discontinuity or self-interaction correction. This presentation shows the mathematically and physically rigorous understanding of the relativistic extension of DFT by Rajagopal and Callaway {Phys. Rev. B 7, 1912 (1973)]. As in the non-relativistic case, the attainment of the absolute minima of the occupied energies is a necessary condition for the corresponding current density to be that of the ground state of the system and for computational results to agree with corresponding, experimental ones. Acknowledgments:This work was funded in part by the US National Science Foundation [NSF, Award Nos. EPS-1003897, NSF (2010-2015)-RII-SUBR, and HRD-1002541], the US Department of Energy, National Nuclear Security Administration (NNSA, Award No. DE-NA0002630), LaSPACE, and LONI-SUBR.

Synthesis, structural, DFT studies, docking and antibacterial activity of a xanthene based hydrazone ligand

NASA Astrophysics Data System (ADS)

Naseem, Saira; Khalid, Muhammad; Tahir, Muhammad Nawaz; Halim, Mohammad A.; Braga, Ataualpa A. C.; Naseer, Muhammad Moazzam; Shafiq, Zahid

2017-09-01

Herein, we present the synthesis of novel xanthene-based hydrazone (1). The chemical structure of 1 was resolved using spectroscopic techniques such as NMR, FT-IR, UV-VIS and X-ray crystallographic approaches. X-ray diffraction analysis shows that the compound (1) crystallizes in triclinic crystal lattice with the Pbar1 space group and diffused to form multi-layered structure due to non-covalent interactions such as intramolecular hydrogen bonding (H.B). In addition to experimental investigation, density functional theory (DFT) calculation with M06-2X/6-31G(d,p) and B3LYP/6-31G(d,p) level of theories was performed on compound (1) to obtain optimized geometry, spectroscopic and electronic properties. DFT optimized geometry shows good agreement with the experimental XRD structure. The hyper conjugative interactions and hydrogen bonding network are responsible for the stability of compound (1) as revealed by natural bond orbital (NBO) calculation. Moreover, hydrogen bonding network in the dimer is confirmed by FT-IR and thermodynamic studies showing excellent agreement with XRD and NBO findings. TD-DFT/UV-VIS analysis provides insight that maximum excitation is found in 1 which shows good agreement with experimental UV-VIS result. The global reactivity parameters are calculated using the energies of frontier molecular orbitals also disclosed that the compound is more stable might be due to hydrogen bonding network. Experimental and molecular docking studies indicated that this compound has anti-bacterial and anti-diabetic properties. The binding affinity of this compound against the multidrug efflux pump subunit AcrB OS=Escherichia coli (strain K12) and Human Pancreatic Alpha-Amylase is -9.2 and -10.00 kcal/mol which are higher than the control drugs. Pi-Pi, Pi-anaion, amide-pi and pi-alkyl bonds play key role in drug-protein complexes.

A pipeline design of a fast prime factor DFT on a finite field

NASA Technical Reports Server (NTRS)

Truong, T. K.; Hsu, In-Shek; Shao, H. M.; Reed, Irving S.; Shyu, Hsuen-Chyun

1988-01-01

A conventional prime factor discrete Fourier transform (DFT) algorithm is used to realize a discrete Fourier-like transform on the finite field, GF(q sub n). This algorithm is developed to compute cyclic convolutions of complex numbers and to decode Reed-Solomon codes. Such a pipeline fast prime factor DFT algorithm over GF(q sub n) is regular, simple, expandable, and naturally suitable for VLSI implementation. An example illustrating the pipeline aspect of a 30-point transform over GF(q sub n) is presented.

Molecular structure and spectroscopic investigation of sodium(E)-2-hydroxy-5-((4-sulfonatophenyl)diazenyl)benzoate: A DFT study

NASA Astrophysics Data System (ADS)

Shahab, Siyamak; Kumar, Rakesh; Darroudi, Mahdieh; Yousefzadeh Borzehandani, Mostafa

2015-03-01

Quantum-chemical calculations using the Density Functional Theory (DFT) approach for structural analysis of new azodye sodium(E)-2-hydroxy-5-((4-sulfonatophenyl)diazenyl) (trans isomer) is carried out using B3LYP methods with 6-31G∗ basis set. The comparison of measured UV-Vis data, IR and NMR spectra of the molecule with the experimental data were also described which allowed assignment of major spectral features of title molecule. The optimized geometrical parameters obtained by B3LYP methods show a good agreement with experimental data. On the basis of polyvinyl alcohol (PVA) and the dichroic synthesized dye polarizer absorbing in the UV region of the spectrum (λmax = 353 nm) with the effect of polarization in the absorption maximum 96% was developed. The spectral-polarization parameters of stretched PVA-films were calculated.

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.

Charge transfer properties of pentacene adsorbed on silver: DFT study

NASA Astrophysics Data System (ADS)

N, Rekha T.; Rajkumar, Beulah J. M.

2015-06-01

Charge transfer properties of pentacene adsorbed on silver is investigated using DFT methods. Optimized geometry of pentacene after adsorption on silver indicates distortion in hexagonal structure of the ring close to the silver cluster and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles. Theoretically simulated absorption spectrum has a symmetric surface plasmon resonance peak around 486nm corresponding to the transfer of charge from HOMO-2 to LUMO. Theoretical SERS confirms the process of adsorption, tilted orientation of pentacene on silver surface and the charge transfers reported. Localization of electron density arising from redistribution of electrostatic potential together with a reduced bandgap of pentacene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices.

Metal alkyls programmed to generate metal alkylidenes by α-H abstraction: prognosis from NMR chemical shift† †Electronic supplementary information (ESI) available: Experimental and computational details, NMR spectra, results of NMR calculations and NCS analysis, graphical representation of shielding tensors, molecular orbital diagrams of selected compounds, optimized structures for all calculated species. See DOI: 10.1039/c7sc05039a

PubMed Central

Gordon, Christopher P.; Yamamoto, Keishi; Searles, Keith; Shirase, Satoru

2018-01-01

Metal alkylidenes, which are key organometallic intermediates in reactions such as olefination or alkene and alkane metathesis, are typically generated from metal dialkyl compounds [M](CH2R)2 that show distinctively deshielded chemical shifts for their α-carbons. Experimental solid-state NMR measurements combined with DFT/ZORA calculations and a chemical shift tensor analysis reveal that this remarkable deshielding originates from an empty metal d-orbital oriented in the M–Cα–Cα′ plane, interacting with the Cα p-orbital lying in the same plane. This π-type interaction inscribes some alkylidene character into Cα that favors alkylidene generation via α-H abstraction. The extent of the deshielding and the anisotropy of the alkyl chemical shift tensors distinguishes [M](CH2R)2 compounds that form alkylidenes from those that do not, relating the reactivity to molecular orbitals of the respective molecules. The α-carbon chemical shifts and tensor orientations thus predict the reactivity of metal alkyl compounds towards alkylidene generation. PMID:29675237

A Systematic Theoretical Study of UC6: Structure, Bonding Nature, and Spectroscopy.

PubMed

Du, Jiguang; Jiang, Gang

2017-11-20

The study of uranium carbides has received renewed attention in recent years due to the potential use of these compounds as fuels in new generations of nuclear reactors. The isomers of the UC 6 cluster were determined by DFT and ab initio methods. The structures obtained using SC-RECP for U were generally consistent with those obtained using an all-electron basis set (ZORA-SARC). The CCSD(T) calculations indicated that two isomers had similar energies and may coexist in laser evaporation experiments. The nature of the U-C bonds in the different isomers was examined via a topological analysis of the electron density, and the results indicated that the U-C bonds are predominantly closed-shell (ionic) interactions with a certain degree of covalent character in all cases, particularly in the linear species. The IR and UV-vis spectra of the isomers were theoretically simulated to provide information that can be used to identify the isomers of UC 6 in future experiments.

Techniques for Computing the DFT Using the Residue Fermat Number Systems and VLSI

NASA Technical Reports Server (NTRS)

Truong, T. K.; Chang, J. J.; Hsu, I. S.; Pei, D. Y.; Reed, I. S.

1985-01-01

The integer complex multiplier and adder over the direct sum of two copies of a finite field is specialized to the direct sum of the rings of integers modulo Fermat numbers. Such multiplications and additions can be used in the implementation of a discrete Fourier transform (DFT) of a sequence of complex numbers. The advantage of the present approach is that the number of multiplications needed for the DFT can be reduced substantially over the previous approach. The architectural designs using this approach are regular, simple, expandable and, therefore, naturally suitable for VLSI implementation.

Optimization of auxiliary basis sets for the LEDO expansion and a projection technique for LEDO-DFT.

PubMed

Götz, Andreas W; Kollmar, Christian; Hess, Bernd A

2005-09-01

We present a systematic procedure for the optimization of the expansion basis for the limited expansion of diatomic overlap density functional theory (LEDO-DFT) and report on optimized auxiliary orbitals for the Ahlrichs split valence plus polarization basis set (SVP) for the elements H, Li--F, and Na--Cl. A new method to deal with near-linear dependences in the LEDO expansion basis is introduced, which greatly reduces the computational effort of LEDO-DFT calculations. Numerical results for a test set of small molecules demonstrate the accuracy of electronic energies, structural parameters, dipole moments, and harmonic frequencies. For larger molecular systems the numerical errors introduced by the LEDO approximation can lead to an uncontrollable behavior of the self-consistent field (SCF) process. A projection technique suggested by Löwdin is presented in the framework of LEDO-DFT, which guarantees for SCF convergence. Numerical results on some critical test molecules suggest the general applicability of the auxiliary orbitals presented in combination with this projection technique. Timing results indicate that LEDO-DFT is competitive with conventional density fitting methods. (c) 2005 Wiley Periodicals, Inc.

DFT investigation of electronic structures and magnetic properties of halides family MeHal3 (Me=Ti, Mo,Zr,Nb, Ru, Hal=Cl,Br,I) one dimensional structures

NASA Astrophysics Data System (ADS)

Kuzubov, A. A.; Kovaleva, E. A.; Popova, M. I.; Kholtobina, A. S.; Mikhaleva, N. S.; Visotin, M. A.; Fedorov, A. S.

2017-10-01

Using DFT GGA calculations, electronic structure and magnetic properties of wide family of transition metal trihalides (TMHal3) (Zr, Ti and Nb iodides, Mo, Ru, Ti and Zr bromides and Ti or Zr chlorides) are investigated. These structures consist of transition metal atoms chains surrounded by halides atoms. Chains are connected to each other by weak interactions. All TMHal3 compounds were found to be conductive along chain axis except of MoBr3 which is indirect gap semiconductor. It was shown that NbI3 and MoBr3 have large magnetic moments on metal atoms (1.17 and 1.81 μB, respectively) but other TMHal3 materials have small or zero magnetic moments. For all structures ferromagnetic and anti-ferromagnetic phases have almost the same energies. The causes of these properties are debated.

Calorimetric, FTIR and 1H NMR measurements in combination with DFT calculations for monitoring solid-state changes of dynamics of sibutramine hydrochloride.

PubMed

Pajzderska, Aleksandra; Chudoba, Dorota M; Mielcarek, Jadwiga; Wąsicki, Jan

2012-10-01

Two forms of sibutramine hydrochloride, monohydrate and anhydrous, have been investigated by calorimetric methods, Fourier transform infrared (FTIR) absorption and (1) H nuclear magnetic resonance (NMR) measurements as well as by density functional theory (DFT) of vibrational frequencies and infrared intensities, calculations of steric hindrances and Monte Carlo simulations. The results of FTIR spectra combined with DFT calculations permitted identification of the bands corresponding to the dynamics and vibrations of water molecules. NMR study and Monte Carlo simulations revealed the occurrence of reorientation jumps of the methyl groups in sibutramine cation and also revealed that the reorientation of isopropyl group is possible only in sibutramine monohydrate hydrochloride. The hydration of sibutramine hydrochloride causes a change in the conformation of sibutramine cation. Copyright © 2012 Wiley-Liss, Inc.

Nonlinear d10-ML2 Transition-Metal Complexes

PubMed Central

Wolters, Lando P; Bickelhaupt, F Matthias

2013-01-01

We have investigated the molecular geometries of a series of dicoordinated d10-transition-metal complexes ML2 (M=Co−, Rh−, Ir−, Ni, Pd, Pt, Cu+, Ag+, Au+; L=NH3, PH3, CO) using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. Not all complexes have the expected linear ligand–metal–ligand (L–M–L) angle: this angle varies from 180° to 128.6° as a function of the metal as well as the ligands. Our main objective is to present a detailed explanation why ML2 complexes can become bent. To this end, we have analyzed the bonding mechanism in ML2 as a function of the L–M–L angle using quantitative Kohn–Sham molecular orbital (MO) theory in combination with an energy decomposition analysis (EDA) scheme. The origin of bent L–M–L structures is π backdonation. In situations of strong π backdonation, smaller angles increase the overlap of the ligand’s acceptor orbital with a higher-energy donor orbital on the metal-ligand fragment, and therefore favor π backdonation, resulting in additional stabilization. The angle of the complexes thus depends on the balance between this additional stabilization and increased steric repulsion that occurs as the complexes are bent. PMID:24551547

Combining DFT, Cluster Expansions, and KMC to Model Point Defects in Alloys

NASA Astrophysics Data System (ADS)

Modine, N. A.; Wright, A. F.; Lee, S. R.; Foiles, S. M.; Battaile, C. C.; Thomas, J. C.; van der Ven, A.

In an alloy, defect energies are sensitive to the occupations of nearby atomic sites, which leads to a distribution of defect properties. When radiation-induced defects diffuse from their initially non-equilibrium locations, this distribution becomes time-dependent. The defects can become trapped in energetically favorable regions of the alloy leading to a diffusion rate that slows dramatically with time. Density Functional Theory (DFT) allows the accurate determination of ground state and transition state energies for a defect in a particular alloy environment but requires thousands of processing hours for each such calculation. Kinetic Monte-Carlo (KMC) can be used to model defect diffusion and the changing distribution of defect properties but requires energy evaluations for millions of local environments. We have used the Cluster Expansion (CE) formalism to ``glue'' together these seemingly incompatible methods. The occupation of each alloy site is represented by an Ising-like variable, and products of these variables are used to expand quantities of interest. Once a CE is fit to a training set of DFT energies, it allows very rapid evaluation of the energy for an arbitrary configuration, while maintaining the accuracy of the underlying DFT calculations. These energy evaluations are then used to drive our KMC simulations. We will demonstrate the application of our DFT/MC/KMC approach to model thermal and carrier-induced diffusion of intrinsic point defects in III-V alloys. 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.

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.

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.

Optical Gaps in Pristine and Heavily Doped Silicon Nanocrystals: DFT versus Quantum Monte Carlo Benchmarks.

PubMed

Derian, R; Tokár, K; Somogyi, B; Gali, Á; Štich, I

2017-12-12

We present a time-dependent density functional theory (TDDFT) study of the optical gaps of light-emitting nanomaterials, namely, pristine and heavily B- and P-codoped silicon crystalline nanoparticles. Twenty DFT exchange-correlation functionals sampled from the best currently available inventory such as hybrids and range-separated hybrids are benchmarked against ultra-accurate quantum Monte Carlo results on small model Si nanocrystals. Overall, the range-separated hybrids are found to perform best. The quality of the DFT gaps is correlated with the deviation from Koopmans' theorem as a possible quality guide. In addition to providing a generic test of the ability of TDDFT to describe optical properties of silicon crystalline nanoparticles, the results also open up a route to benchmark-quality DFT studies of nanoparticle sizes approaching those studied experimentally.

Geometric interpretations of the Discrete Fourier Transform (DFT)

NASA Technical Reports Server (NTRS)

Campbell, C. W.

1984-01-01

One, two, and three dimensional Discrete Fourier Transforms (DFT) and geometric interpretations of their periodicities are presented. These operators are examined for their relationship with the two sided, continuous Fourier transform. Discrete or continuous transforms of real functions have certain symmetry properties. The symmetries are examined for the one, two, and three dimensional cases. Extension to higher dimension is straight forward.

Vibrational spectral investigation and natural bond orbital analysis of pharmaceutical compound 7-Amino-2,4-dimethylquinolinium formate - DFT approach

NASA Astrophysics Data System (ADS)

Suresh, D. M.; Amalanathan, M.; Sebastian, S.; Sajan, D.; Hubert Joe, I.; Bena Jothy, V.; Nemec, Ivan

2013-11-01

The molecular geometry, the normal mode frequencies and corresponding vibrational assignments, natural bond orbital analysis and the HOMO-LUMO analysis of 7-Amino-2,4-dimethylquinolinium formate in the ground state were performed by B3LYP levels of theory using the 6-31G(d) basis set. The optimised bond lengths and bond angles are in good agreement with the X-ray data. The vibrational spectra of the title compound which is calculated by DFT method, reproduces vibrational wave numbers and intensities with an accuracy which allows reliable vibrational assignments. The possibility of N-H⋯O hydrogen bonding was identified using NBO analysis. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction.

The plane-wave DFT investigations into the structure and the 11B solid-state NMR parameters of lithium fluorooxoborates

NASA Astrophysics Data System (ADS)

Czernek, Jiří; Brus, Jiří

2016-12-01

The strategy for an application of the first-principles calculations on crystalline systems to predict the 11B solid-state NMR powder-patterns is described, and its efficacy is demonstrated for two novel lithium-containing fluorooxborates, Li2B3O4F3 and Li2B6O9F2. This strategy involves the plane-wave DFT computations of the NMR parameters, whose values are then scaled and used in the spectral simulations, and are supposed to be directly applicable in the NMR crystallography studies of boron-containing systems. In particular, the GIPAW method and the PBE, PW91, and RPBE functionals are applied. Issues specific to the signal-assignment of the two compounds are also discussed.

Synthesis, structural and vibrational investigation on 2-phenyl-N-(pyrazin-2-yl)acetamide combining XRD diffraction, FT-IR and NMR spectroscopies with DFT calculations.

PubMed

Lukose, Jilu; Yohannan Panicker, C; Nayak, Prakash S; Narayana, B; Sarojini, B K; Van Alsenoy, C; Al-Saadi, Abdulaziz A

2015-01-25

The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of 2-phenyl-N-(pyrazin-2-yl)acetamide have been investigated experimentally and theoretically using Gaussian09 software package. The title compound was optimized by using the HF/6-31G(6D,7F) and B3LYP/6-31G(6D,7F) calculations. The geometrical parameters are in agreement with the XRD data. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. Gauge-including atomic orbital (1)H-NMR chemical shifts calculations were carried out and compared with experimental data. The HOMO and LUMO analysis is used to determine the charge transfer within the molecule. Molecular electrostatic potential was performed by the DFT method. First hyperpolarizability is calculated in order to find its role in non linear optics. From the XRD data, in the crystal, molecules are held together by strong C-H⋯O and N-H⋯O intermolecular interactions. Copyright © 2014 Elsevier B.V. All rights reserved.

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

Simulated structure and imaging of NTCDI on Si(1 1 1)-7 × 7 : a combined STM, NC-AFM and DFT study

NASA Astrophysics Data System (ADS)

Jarvis, S. P.; Sweetman, A. M.; Lekkas, I.; Champness, N. R.; Kantorovich, L.; Moriarty, P.

2015-02-01

The adsorption of naphthalene tetracarboxylic diimide (NTCDI) on Si(1 1 1)-7 × 7 is investigated through a combination of scanning tunnelling microscopy (STM), noncontact atomic force microscopy (NC-AFM) and density functional theory (DFT) calculations. We show that NTCDI adopts multiple planar adsorption geometries on the Si(1 1 1)-7 × 7 surface which can be imaged with intramolecular bond resolution using NC-AFM. DFT calculations reveal adsorption is dominated by covalent bond formation between the molecular oxygen atoms and the surface silicon adatoms. The chemisorption of the molecule is found to induce subtle distortions to the molecular structure, which are observed in NC-AFM images.

Synthesis, characterization, spectroscopic properties and DFT study of a new pyridazinone family

NASA Astrophysics Data System (ADS)

Arrue, Lily; Rey, Marina; Rubilar-Hernandez, Carlos; Correa, Sebastian; Molins, Elies; Norambuena, Lorena; Zarate, Ximena; Schott, Eduardo

2017-11-01

Nitrogen compounds are widely investigated due to their pharmacological properties such as antihypertensive, antinociceptive, antibacterial, antifungal, analgesic, anticancer and inhibition activities and lately even as pesticide. In this context, we present the synthesis of new compounds: (E)-6-(3,4-dimethoxyphenyl)-3-(3-(3,4-dimethoxyphenyl)acryloyl)-1-(4-R-phenyl)- 5,6-dihydropyridazin-4(1H)-one (with R = sbnd H(1), -Cl(2), -Br(3), sbnd I(4) and sbnd COOH(5)) that was carried out by reaction of (1E, 6E)-1,7-bis(3,4-dimethoxyphenyl)hepta-1,6-diene-3,5-dione with a substituted phenylamine with general formula p-R-C6H4sbnd NH2 (R = sbnd H (1), sbnd Cl (2), -Br(3), sbnd I(4) and sbnd COOH(5)). This is the first synthesis report of a pyridazinone using as precursors a curcuminoid derivative and a diazonium salt formed in situ. All compounds were characterized by EA, FT-IR, UV-Vis, Emission,1H- and13C-NMR spectroscopy and the crystalline and molecular structure of 4 was solved by X-rays diffraction method. DFT and TD-DFT quantum chemical calculations were also employed to characterize the compounds and provide a rational explanation to the spectroscopic properties. To assess the biological activity of the systems, we focused on pesticide tests on compound 2, which showed an inhibitory effect in plant growth of Agrostis tenuis Higland.

Structure Determination of Au on Pt(111) Surface: LEED, STM and DFT Study

PubMed Central

Krupski, Katarzyna; Moors, Marco; Jóźwik, Paweł; Kobiela, Tomasz; Krupski, Aleksander

2015-01-01

Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations have been used to investigate the atomic and electronic structure of gold deposited (between 0.8 and 1.0 monolayer) on the Pt(111) face in ultrahigh vacuum at room temperature. The analysis of LEED and STM measurements indicates two-dimensional growth of the first Au monolayer. Change of the measured surface lattice constant equal to 2.80 Å after Au adsorption was not observed. Based on DFT, the distance between the nearest atoms in the case of bare Pt(111) and Au/Pt(111) surface is equal to 2.83 Å, which gives 1% difference in comparison with STM values. The first and second interlayer spacing of the clean Pt(111) surface are expanded by +0.87% and contracted by −0.43%, respectively. The adsorption energy of the Au atom on the Pt(111) surface is dependent on the adsorption position, and there is a preference for a hollow fcc site. For the Au/Pt(111) surface, the top interlayer spacing is expanded by +2.16% with respect to the ideal bulk value. Changes in the electronic properties of the Au/Pt(111) system below the Fermi level connected to the interaction of Au atoms with Pt(111) surface are observed.

DFT and ab initio study of the unimolecular decomposition of the lowest singlet and triplet states of nitromethane

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

Manaa, M.R.; Fried, L.E.

1998-11-26

The fully optimized potential energy curves for the unimolecular decomposition of the lowest singlet and triplet states of nitromethane through the C-NO{sub 2} bond dissociation pathway are calculated using various DFT and high-level ab initio electronic structure methods. The authors perform gradient corrected density functional theory (DFT) and multiconfiguration self-consistent field (MCSCF) to conclusively demonstrate that the triplet state of nitromethane is bound. The adiabatic curve of this state exhibits a 33 kcal/mol energy barrier as determined at the MCSCF level. DFT methods locate this barrier at a shorter C-N bond distance with 12--16 kcal/mol lower energy than does MCSCF.more » In addition to MCSCF and DFT, quadratic configuration interactions with single and double substitutions (QCISD) calculations are also performed for the singlet curve. The potential energy profiles of this state predicted by FT methods based on Becke`s 1988 exchange functional differ by as much as 17 kcal/mol from the predictions of MCSCF and QCISD in the vicinity of the equilibrium structure. The computational methods predict bond dissociation energies 5--9 kcal/mol lower than the experimental value. DFT techniques based on Becke`s 3-parameter exchange functional show the best overall agreement with the higher level methods.« less

Diffusion of anthracene derivatives on Cu(111) studied by STM and DFT

NASA Astrophysics Data System (ADS)

Wyrick, Jonathan; Bartels, Ludwig; Einstein, Theodore

2014-03-01

Substituted anthracenes have drawn attention due to their ability to diffuse uniaxially on a Cu(111) surface. We compare anthracene to three of its derivatives whose 9,10 hydrogens are replaced by elements of the chalcogen group that act as linkers binding the molecules to a Cu(111) substrate. DFT calculations shed light on STM imaging and diffusion studies on the three substituted species. We present an analysis of the DFT results in which energetic contributions to the diffusion barriers are partitioned among the Kohn-Sham orbitals, allowing us to make assignments as to how each orbital affects diffusion for each species and draw comparisons between them. Present address: Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD.

Investigation of synthesized new vanadium(III) complexes of ditolyldithiophosphate ligands by spectroscopic, cyclic voltammetric, DFT, antimicrobial and cytotoxic studies

NASA Astrophysics Data System (ADS)

Kumar, Sandeep; Syed, Atiya; Andotra, Savit; Kaur, Ramanpreet; Vikas; Pandey, Sushil K.

2018-02-01

Vanadium(III) complexes with sulfur donor dithiophosphate ligands corresponding to [{(ArO)2PS2}3V] and [{(ArO)2PS2}2VCl.L] (Ar = o-, m-, p-CH3C6H4 and p-Cl-m-CH3C6H3; L = NC5H5, P(C6H5)3, have been synthesized and characterized by various physico-chemical techniques like elemental analyses, magnetic studies, ESI-Mass, IR, UV and heteronuclear NMR (1H, 13C and 31P) spectral studies. These analyses have contributed to the prediction of structure: by exhibiting significant v(P-S) and v(Pdbnd S) band shifting in comparative IR spectra; shifting of resonance signal in comparative 31P NMR spectra of ligands and complexes and stability of V(III) ion in the complexed state is confirmed by magnetic and UV studies. Therefore, the six coordinated geometry stabilizing the trivalent vanadium atom in the complexes and adducts, respectively has been confirmed. The cyclic voltammetric analyses presented the redox aptitude of the complex under analysis which can be utilized as catalyst in organic synthesis. The geometry of ligands and complexes has been optimized using density functional theory (DFT). The structural parameters, vibrational bands and energy gaps of frontier orbitals (HOMO-LUMO) have also been calculated. The calculated geometric and spectral results reproduced the experimental data with well agreement. The DFT computed frontier molecular orbitals (HOMO-LUMO) and their energies suggest charge transfer occurs within the complexes. Antimicrobial screening of the complexes against two bacterial strains: Gram-positive, Enterrococcus faecalis and Gram-negative, Eischerichia coli and fungus Fusarium oxysporum have shown potential bioactivity. A preliminary cytotoxic analysis has been carried out using the cultivated human cell lines: lung adeno carcinoma cell line A-549, leukemia cell line THP-1, prostate cancer cell line PC3 and colorectal cancer cell line HCT-116.

Vibrational spectral investigation and natural bond orbital analysis of pharmaceutical compound 7-Amino-2,4-dimethylquinolinium formate - DFT approach.

PubMed

Suresh, D M; Amalanathan, M; Sebastian, S; Sajan, D; Hubert Joe, I; Bena Jothy, V; Nemec, Ivan

2013-11-01

The molecular geometry, the normal mode frequencies and corresponding vibrational assignments, natural bond orbital analysis and the HOMO-LUMO analysis of 7-Amino-2,4-dimethylquinolinium formate in the ground state were performed by B3LYP levels of theory using the 6-31G(d) basis set. The optimised bond lengths and bond angles are in good agreement with the X-ray data. The vibrational spectra of the title compound which is calculated by DFT method, reproduces vibrational wave numbers and intensities with an accuracy which allows reliable vibrational assignments. The possibility of N-H⋯O hydrogen bonding was identified using NBO analysis. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

New Pyrazole-Hydrazone Derivatives: X-ray Analysis, Molecular Structure Investigation via Density Functional Theory (DFT) and Their High In-Situ Catecholase Activity.

PubMed

Karrouchi, Khalid; Yousfi, El Bekkaye; Sebbar, Nada Kheira; Ramli, Youssef; Taoufik, Jamal; Ouzidan, Younes; Ansar, M'hammed; Mabkhot, Yahia N; Ghabbour, Hazem A; Radi, Smaail

2017-10-25

The development of low-cost catalytic systems that mimic the activity of tyrosinase enzymes (Catechol oxidase) is of great promise for future biochemistry technologic demands. Herein, we report the synthesis of new biomolecules systems based on hydrazone derivatives containing a pyrazole moiety ( L1 - L6 ) with superior catecholase activity. Crystal structures of L1 and L2 biomolecules were determined by X-ray single crystal diffraction (XRD). Optimized geometrical parameters were calculated by density functional theory (DFT) at B3LYP/6-31G (d, p) level and were found to be in good agreement with single crystal XRD data. Copper (II) complexes of the compounds ( L1 - L6 ), generated in-situ, were investigated for their catalytic activities towards the oxidation reaction of catechol to ortho -quinone with the atmospheric dioxygen, in an attempt to model the activity of the copper containing enzyme tyrosinase. The studies showed that the activities depend on four parameters: the nature of the ligand, the nature of counter anion, the nature of solvent and the concentration of ligand. The Cu(II)-ligands, given here, present the highest catalytic activity (72.920 μmol·L -1 ·min -1 ) among the catalysts recently reported in the existing literature.

Structures, mechanical properties, equations of state, and electronic properties of β-HMX under hydrostatic pressures: a DFT-D2 study.

PubMed

Peng, Qing; Rahul; Wang, Guangyu; Liu, Gui-Rong; De, Suvranu

2014-10-07

We report the hydrostatic compression studies of the β-polymorph of a cyclotetramethylene tetranitramine (HMX) energetic molecular crystal using DFT-D2, a first-principles calculation based on density functional theory (DFT) with van der Waals (vdW) corrections. The molecular structure, mechanical properties, electronic properties, and equations of state of β-HMX are investigated. For the first time, we predict the elastic constants of β-HMX using DFT-D2 studies. The equations of state under hydrostatic compression are studied for pressures up to 100 GPa. We found that the N-N bonds along the minor axis are responsible for the sensitivity of β-HMX. The analysis of the charge distribution shows that the electronic charge is transferred from hydrogen atoms to nitro groups with the amount of 0.131 and 0.064e for the nitro groups along the minor axis and major axis, respectively, when pressure changes from 0 GPa to 100 GPa. The electronic energy band gap changes from direct at a pressure of 0 GPa to indirect at a pressure of 50 GPa and higher. The band gap decreases with respect to an increase in pressure, implying that the impact sensitivity increases with compression. Our study suggests that the van der Waals interactions are critically important in modeling the mechanical properties of this molecular crystal.

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.

Chemical shielding properties for BN, BP, AlN, and AlP nanocones: DFT studies

NASA Astrophysics Data System (ADS)

Mirzaei, Mahmoud; Yousefi, Mohammad; Meskinfam, Masoumeh

2012-06-01

The properties of boron nitride (BN), boron phosphide (BP), aluminum nitride (AlN), and aluminum phosphide (AlP) nanocones were investigated by density functional theory (DFT) calculations. The investigated structures were optimized and chemical shielding (CS) properties including isotropic and anisotropic CS parameters were calculated for the atoms of the optimized structures. The magnitudes of CS parameters were observed to be mainly dependent on the bond lengths of considered atoms. The results indicated that the atoms could be divided into atomic layers due to the similarities of their CS properties for the atoms of each layer. The trend means that the atoms of each layer detect almost similar electronic environments. Moreover, the atoms at the apex and mouth of nanocones exhibit different properties with respect to the other atomic layers.

Solvatochromic benzo[h] coumarins: Synthesis, solvatochromism, NLO and DFT study

NASA Astrophysics Data System (ADS)

Warde, Umesh; Sekar, Nagaiyan

2017-10-01

Three benzo[h] coumarins were synthesized and analyzed for their potential NLOphoric properties. Coumarins were synthesized using Knoevenagel condensation method by reacting hydroxyl-naphthalene aldehyde with cyano-methylelene-benzazoles containing NH, O and S elements respectively as the active methylene compounds. The absorption maxima for the coumarins are not affected by the solvent polarity but emission maxima does. Emission solvatochromism was analyzed using various solvent polarity functions which highlights the polarity dependency of the emission profile. Coumarins showed satisfactory values for first and second hyperpolarizability which are comparable using solvatochromism and DFT. NLO properties are also compared with the limits of hyperpolarizability calculated using sum rule of quantum mechanics. Results show that the NLO properties predicted by DFT are close to the upper limits of hyperpolarizability. The functional CAM-B3LYP is proven to be suitable for predicting NLO properties for these coumarins compared to functional B3LYP. The present study highlights the importance of such molecules for incorporating in advanced NLOphores.

Accuracy of Td-DFT in the Ultraviolet and Circular Dichroism Spectra of Deoxyguanosine and Uridine.

PubMed

Miyahara, Tomoo; Nakatsuji, Hiroshi

2018-01-11

Accuracy of the time-dependent density functional theory (Td-DFT) was examined for the ultraviolet (UV) and circular dichroism (CD) spectra of deoxyguanosine (dG) and uridine, using 11 different DFT functionals and two different basis sets. The Td-DFT results of the UV and CD spectra were strongly dependent on the functionals used. The basis-set dependence was observed only for the CD spectral calculations. For the UV spectra, the B3LYP and PBE0 functionals gave relatively good results. For the CD spectra, the B3LYP and PBE0 with 6-311G(d,p) basis gave relatively permissible result only for dG. The results of other functionals were difficult to be used for the studies of the UV and CD spectra, though the symmetry adapted cluster-configuration interaction (SAC-CI) method reproduced well the experimental spectra of these molecules. To obtain valuable information from the theoretical calculations of the UV and CD spectra, the theoretical tool must be able to reproduce correctly both of the intensities and peak positions of the UV and CD spectra. Then, we can analyze the reasons of the changes of the intensity and/or the peak position to clarify the chemistry involved. It is difficult to recommend Td-DFT as such tools of science, at least from the examinations using dG and uridine.

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.

A DFT+U investigation of hydrogen adsorption on the LaFeO3(010) surface.

PubMed

Boateng, Isaac W; Tia, Richard; Adei, Evans; Dzade, Nelson Y; Catlow, C Richard A; de Leeuw, Nora H

2017-03-08

The ABO 3 perovskite lanthanum ferrite (LaFeO 3 ) is a technologically important electrode material for nickel-metal hydride batteries, energy storage and catalysis. However, the electrochemical hydrogen adsorption mechanism on LaFeO 3 surfaces remains under debate. In the present study, we have employed spin-polarized density functional theory calculations, with the Hubbard U correction (DFT+U), to unravel the adsorption mechanism of H 2 on the LaFeO 3 (010) surface. We show from our calculated adsorption energies that the preferred site for H 2 adsorption is the Fe-O bridge site, with an adsorption energy of -1.18 eV (including the zero point energy), which resulted in the formation of FeOH and FeH surface species. H 2 adsorption at the surface oxygen resulted in the formation of a water molecule, which leaves the surface to create an oxygen vacancy. The H 2 molecule is found to interact weakly with the Fe and La sites, where it is only physisorbed. The electronic structures of the surface-adsorption systems are discussed via projected density of state and Löwdin population analyses. The implications of the calculated adsorption strengths and structures are discussed in terms of the improved design of nickel-metal hydride (Ni-MH) battery prototypes based on LaFeO 3 .

The crystal structure of sulfamethoxazole, interaction with DNA, DFT calculation, and molecular docking studies

NASA Astrophysics Data System (ADS)

Das, Dipankar; Sahu, Nilima; Roy, Suman; Dutta, Paramita; Mondal, Sudipa; Torres, Elena L.; Sinha, Chittaranjan

2015-02-01

Sulfamethoxazole (SMX) [4-amino-N-(5-methyl-1,2-oxazol-3-yl)benzenesulfonamide] is structurally established by single crystal X-ray diffraction measurement. The crystal packing shows H-bonded 2D polymer through N(7)sbnd H(7A)---O(2), N(7)sbnd H(7B)---O(3), N(1)sbnd H(1)---N(2), C(5)sbnd H(5)---O(3)sbnd S(1) and N(7)sbnd (H7A)---O(2)sbnd S(1). Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) computations of optimized structure of SMX determine the electronic structure and has explained the electronic spectral transitions. The interaction of SMX with CT-DNA has been studied by absorption spectroscopy and the binding constant (Kb) is 4.37 × 104 M-1. The in silico test of SMX with DHPS from Escherichia coli and Streptococcus pneumoniae helps to understand drug metabolism and accounts the drug-molecule interactions. The molecular docking of SMX-DNA also helps to predict the interaction feature.

Combined MCD/DFT/TDDFT Study of the Electronic Structure of Axially Pyridine Coordinated Metallocorroles.

PubMed

Rhoda, Hannah M; Crandall, Laura A; Geier, G Richard; Ziegler, Christopher J; Nemykin, Victor N

2015-05-18

A series of metallocorroles were investigated by UV-vis and magnetic circular dichroism spectroscopies. The diamagnetic distorted square-pyramidal main-group corrole Ga(tpfc)py (2), the diamagnetic distorted octahedral transition-metal adduct Co(tpfc)(py)2 (3), and paramagnetic distorted octahedral transition-metal complex Fe(tpfc)(py)2 (4) [H3tpfc = tris(perfluorophenyl)corrole] were studied to investigate similarities and differences in the electronic structure and spectroscopy of the closed- and open-shell metallocorroles. Similar to the free-base H3tpfc (1), inspection of the MCD Faraday B-terms for all of the macrocycles presented in this report revealed that a ΔHOMO < ΔLUMO [ΔHOMO is the energy difference between two highest energy corrole-centered π-orbitals and ΔLUMO is the energy difference between two lowest energy corrole-centered π*-orbitals originating from ML ± 4 and ML ± 5 pairs of perimeter] condition is present for each complex, which results in an unusual sign-reversed sequence for π-π* transitions in their MCD spectra. In addition, the MCD spectra of the cobalt and the iron complexes were also complicated by a number of charge-transfer states in the visible region. Iron complex 4 also exhibits a low-energy absorption in the NIR region (1023 nm). DFT and TDDFT calculations were used to elaborate the electronic structures and provide band assignments in UV-vis and MCD spectra of the metallocorroles. DFT and TDDFT calculations predict that the orientation of the axial pyridine ligand(s) has a very minor influence on the calculated electronic structures and absorption spectra in the target systems.

Evaluation of DFT methods for computing the interaction energies of homomolecular and heteromolecular dimers of monosubstituted benzene

NASA Astrophysics Data System (ADS)

Godfrey-Kittle, Andrew; Cafiero, Mauricio

We present density functional theory (DFT) interaction energies for the sandwich and T-shaped conformers of substituted benzene dimers. The DFT functionals studied include TPSS, HCTH407, B3LYP, and X3LYP. We also include Hartree-Fock (HF) and second-order Møller-Plesset perturbation theory calculations (MP2), as well as calculations using a new functional, P3LYP, which includes PBE and HF exchange and LYP correlation. Although DFT methods do not explicitly account for the dispersion interactions important in the benzene-dimer interactions, we find that our new method, P3LYP, as well as HCTH407 and TPSS, match MP2 and CCSD(T) calculations much better than the hybrid methods B3LYP and X3LYP methods do.

Melamine derivatives as effective corrosion inhibitors for mild steel in acidic solution: Chemical, electrochemical, surface and DFT studies

NASA Astrophysics Data System (ADS)

Verma, Chandrabhan; Haque, J.; Ebenso, Eno E.; Quraishi, M. A.

2018-06-01

In present study two condensation products of melamine (triazine) and glyoxal namely, 2,2-bis(4,6-diamino-1,3,5-triazin-2-ylamino)acetaldehyde (ME-1) and (N2,N2‧E,N2,N2‧E)-N2,N2‧-(ethane-1,2-diylidene)-bis-(1,3,5-triazine-2,4,6-triamine) (ME-2) are tested as mild steel corrosion inhibitors in acidic solution (1M HCl). The inhibition efficiency of ME-1 and ME-2 increases with increase in their concentrations and maximum values of 91.47% and 94.88% were derived, respectively at 100 mgL-1 (34.20 × 10-5 M) concentration. Adsorption of ME-1 and ME-2 on the surface of metal obeyed the Langmuir adsorption isotherm. Polarization investigation revealed that ME-1 and ME-2 act as mixed type inhibitors with minor cathodic prevalence. The chemical and electrochemical analyses also supported by surface characterization methods where significant smoothness in the surface morphologies was observed in the images of SEM and AFM spectra. Several DFT indices such as EHOMO and ELUMO, ΔE, η, σ, χ, μ and ΔN were derived for both ME-1 and ME-2 molecules and correlated with experimental results. The DFT studies have also been carried out for protonated or cationic form of the inhibitor molecules by considering that in acidic medium the heteroatoms of organic inhibitors easily undergo protonation. The experimental and density functional theory (DFT) studies (neutral and protonated) were in good agreement.

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

A comparative study of DFT calculated and experimental UV/Visible spectra for thirty carboline and carbazole based compounds

NASA Astrophysics Data System (ADS)

Zara, Zeenat; Iqbal, Javed; Ayub, Khurshid; Irfan, Muhammad; Mahmood, Athar; Khera, Rasheed Ahmad; Eliasson, Bertil

2017-12-01

A comparative study of UV/Visible spectra of carboline and carbazole derivatives was conducted by employing the Density Functional Theory (DFT) approach. In this study, the geometries of ground and excited states, excitation energy and absorption spectra were estimated by using seven different DFT functional; CAM-B3LYP, B3LYP, MPW1PW91, PBE, B3PW91, WB97XD and HSE06 with 6-31G basis set. Moreover, five different basis sets 3-21G, 6-31G, DGDZVP, DGTZVP and SDD were also investigated with the CAM-B3LYP and WB97XD functional to take out the best combination of functional and basis set. CAM-B3LYP/6-31G and WB97XD/DGDZVP combination were found to have closest agreement with the experimental values of β-carboline derivatives and carbazole derivatives, respectively. This study provided an insight about the electronic characteristics of the selected compounds and provided an effective tool for developing and designing the better UV absorber compounds.

Cyclopentadienyl ruthenium-nickel catalysts for biomimetic hydrogen evolution: electrocatalytic properties and mechanistic DFT studies.

PubMed

Canaguier, Sigolène; Vaccaro, Loredana; Artero, Vincent; Ostermann, Rainer; Pécaut, Jacques; Field, Martin J; Fontecave, Marc

2009-09-21

The new dinuclear nickel-ruthenium complexes [Ni(xbsms)RuCp(L)][PF(6)] (H(2)xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene; Cp(-) = cyclopentadienyl; L = DMSO, CO, PPh(3), and PCy(3)) are reported and are bioinspired mimics of NiFe hydrogenases. These compounds were characterized by X-ray diffraction techniques and display novel structural motifs. Interestingly, [Ni(xbsms)RuCpCO][PF(6)] is stereochemically nonrigid in solution and an isomerization mechanism was derived with the help of density functional theory (DFT) calculations. Because of an increased electron density on the metal centers [Eur. J. Inorg. Chem. 2007, 18, 2613-2626] with respect to the previously described [Ni(xbsms)Ru(CO)(2)Cl(2)] and [Ni(xbsms)Ru(p-cymene)Cl](+) complexes, [Ni(xbsms)RuCp(dmso)][PF(6)] catalyzes hydrogen evolution from Et(3)NH(+) in DMF with an overpotential reduced by 180 mV and thus represents the most efficient NiFe hydrogenase functional mimic. DFT calculations were carried out with several methods to investigate the catalytic cycle and, coupled with electrochemical measurements, allowed a mechanism to be proposed. A terminal or bridging hydride derivative was identified as the active intermediate, with the structure of the bridging form similar to that of the Ni-C active state of NiFe hydrogenases.

Conformational analysis, X-ray crystallographic, FT-IR, FT-Raman, DFT, MEP and molecular docking studies on 1-(1-(3-methoxyphenyl) ethylidene) thiosemicarbazide

NASA Astrophysics Data System (ADS)

Saravanan, R. R.; Seshadri, S.; Gunasekaran, S.; Mendoza-Meroño, R.; Garcia-Granda, S.

2015-03-01

Conformational analysis, X-ray crystallographic, FT-IR, FT-Raman, DFT, MEP and molecular docking studies on 1-(1-(3-methoxyphenyl) ethylidene) thiosemicarbazide (MPET) are investigated. From conformational analysis the examination of the positions of a molecule taken and the energy changes is observed. The docking studies of the ligand MPET with target protein showed that this is a good molecule which docks well with target related to HMG-CoA. Hence MPET can be considered for developing into a potent anti-cholesterol drug. MEP assists in optimization of electrostatic interactions between the protein and the ligand. The MEP surface displays the molecular shape, size and electrostatic potential values. The optimized geometry of the compound was calculated from the DFT-B3LYP gradient calculations employing 6-31G (d, p) basis set and calculated vibrational frequencies are evaluated via comparison with experimental values.

Acylation and deacylation mechanism of Helicobacter pylori AmiF formamidase: A computational DFT study

NASA Astrophysics Data System (ADS)

He, Rongxing; Yang, Qinlei; Li, Ming

2014-04-01

The acylation and deacylation mechanisms of Helicobacter pylori AmiF formamidase were investigated using DFT method. In the constructed active site, residues Glu60, Glu141 and His167 were taken into account besides Lys133 and Cys166. Calculations provided insight on the details of mechanism and explained crucial roles played by Glu60, Glu141 and His167. For acetylation, we proposed a new stepwise mechanism in which the thiol group first attacks the carbon atom of formamide and produces tetrahedral intermediate. In deacylation, Glu60 activates a water molecule to perform nucleophilic attack and then forms an intermediate, which is different from the usually suggested mechanism.

Activation mechanism of ammonium ions on sulfidation of malachite (-201) surface by DFT study

NASA Astrophysics Data System (ADS)

Wu, Dandan; Mao, Yingbo; Deng, Jiushuai; Wen, Shuming

2017-07-01

The activation mechanism of ammonium ions on the sulfidation of malachite (-201) was determined by density functional theory (DFT) calculations. Results of DFT calculations indicated that interlayer sulfidation occurs during the sulfidation process of malachite (-201). The absorption of both the ammonium ion and sulfide ion on the malachite (-201) surface is stronger than that of sulfur ion. After sulfidation was activated with ammonium ion, the Cu 3d orbital peak is closer to the Fermi level and characterized by a stronger peak value. Therefore, the addition of ammonium ions activated the sulfidation of malachite (-201), thereby improving the flotation performance.

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

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.

FT-IR, Laser-Raman spectra and quantum chemical calculations of methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate-A DFT approach

NASA Astrophysics Data System (ADS)

Sert, Yusuf; Sreenivasa, S.; Doğan, H.; Manojkumar, K. E.; Suchetan, P. A.; Ucun, Fatih

2014-06-01

In this study the experimental and theoretical vibrational frequencies of a newly synthesized anti-tumor and anti-inflammatory agent namely, methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate 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, bond angles and torsion angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parameterized, 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.

Synthesis, electronic structure investigation of 3-pentyl-2,6-di(furan-2-yl)piperidin-4-one by FT-IR, FT-Raman and UV-Visible spectral studies and ab initio/DFT calculations.

PubMed

Arockia Doss, M; Savithiri, S; Rajarajan, G; Thanikachalam, V; Anbuselvan, C

2015-12-05

FT-IR and FT-Raman spectra of 3-pentyl-2,6-di(furan-2-yl) piperidin-4-one (3-PFPO) were recorded in the solid phase. The structural and spectroscopic analyses of 3-PFPO were made by using B3LYP/HF level with 6-311++G(d, p) basis set. The fundamental vibrations are assigned on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method and PQS program. Comparison of the observed fundamental vibrational frequencies of 3-PFPO with calculated results by HF and DFT methods indicates that B3LYP is superior to HF method for molecular vibrational problems. The electronic properties such as excitation energies, oscillator strength, wavelengths and HOMO-LUMO energies were obtained by time-dependent DFT (TD-DFT) approach. The polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. The hyperconjugative interaction energy (E((2))) and electron densities of donor (i) and acceptor (j) bonds were calculated using NBO analysis. In addition, MEP and atomic charges of carbon, nitrogen, oxygen and hydrogen were calculated using B3LYP/6-311++G(d, p) level theory. Moreover, thermodynamic properties (heat capacities, entropy and enthalpy) of the title compound at different temperatures were calculated in gas phase. Copyright © 2015 Elsevier B.V. All rights reserved.

DFT, Its Impact on Condensed Matter and on ``Materials-Genome'' Research

NASA Astrophysics Data System (ADS)

Scheffler, Matthias

About 40 years ago, two seminal works demonstrated the power of density-functional theory (DFT) for real materials. These studies by Moruzzi, Janak, and Williams on metals and Yin and Cohen on semiconductors visualized the spatial distribution of electrons, predicted the equation of state of solids, crystal stability, pressure-induced phase transitions, and more. They also stressed the importance of identifying trends by looking at many systems (e.g. the whole transition-metal series). Since then, the field has seen numerous applications of DFT to solids, liquids, defects, surfaces, and interfaces providing important descriptions and explanations as well as predictions of experimentally not yet identified systems. - ∖ ∖ About 10 years ago, G. Ceder and his group [Ref. 3 and references therein] started with high-throughput screening calculations in the spirit of what in 2011 became the ``Materials Genome Initiative''. The idea of high-throughput screening is old (a key example is the ammonia catalyst found by A. Mittasch at BASF more than 100 years ago), but it is now increasingly becoming clear that big data of materials does not only provide direct information but that the data is structured. This enables interpolation, (modest) extrapolation, and new routes towards understanding [Ref. 5 and references therein]. - ∖ ∖ The amount of data created by ``computational materials science'' is significant. For instance, the NoMaD Repository (which includes also data from other repositories, e.g. AFLOWLIB and OQMD) now holds more than 18 million total-energy calculations. In fact, the amount of data of computational materials science is steadily increasing, and about hundred million CPU core hours are nowadays used every day, worldwide, for DFT calculations for materials. - ∖ ∖ The talk will summarize this enormous impact of DFT on materials science, and it will address the next steps, e.g. the issue how to exploit big data of materials for doing forefront

Spectroscopic studies and quantum chemical investigations of (3,4-dimethoxybenzylidene) propanedinitrile

NASA Astrophysics Data System (ADS)

Gupta, Ujval; Kumar, Vinay; Singh, Vivek K.; Kant, Rajni; Khajuria, Yugal

2015-04-01

The Fourier Transform Infrared (FTIR), Ultra-Violet Visible (UV-Vis) spectroscopy and Thermogravimetric (TG) analysis of (3,4-dimethoxybenzylidene) propanedinitrile have been carried out and investigated using quantum chemical calculations. The molecular geometry, harmonic vibrational frequencies, Mulliken charges, natural atomic charges and thermodynamic properties in the ground state have been investigated by using Hartree Fock Theory (HF) and Density Functional Theory (DFT) using B3LYP functional with 6-311G(d,p) basis set. Both HF and DFT methods yield good agreement with the experimental data. Vibrational modes are assigned with the help of Vibrational Energy Distribution Analysis (VEDA) program. UV-Visible spectrum was recorded in the spectral range of 190-800 nm and the results are compared with the calculated values using TD-DFT approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results obtained from the studies of Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) are used to calculate molecular parameters like ionization potential, electron affinity, global hardness, electron chemical potential and global electrophilicity.

The electronic spectra and the structures of the individual copper(II) chloride and bromide complexes in acetonitrile according to steady-state absorption spectroscopy and DFT/TD-DFT calculations

NASA Astrophysics Data System (ADS)

Olshin, Pavel K.; Myasnikova, Olesya S.; Kashina, Maria V.; Gorbunov, Artem O.; Bogachev, Nikita A.; Kompanets, Viktor O.; Chekalin, Sergey V.; Pulkin, Sergey A.; Kochemirovsky, Vladimir A.; Skripkin, Mikhail Yu.; Mereshchenko, Andrey S.

2018-03-01

The results of spectrophotometric study and quantum chemical calculations for copper(II) chloro- and bromocomplexes in acetonitrile are reported. Electronic spectra of the individual copper(II) halide complexes were obtained in a wide spectral range 200-2200 nm. Stability constants of the individual copper(II) halide complexes in acetonitrile were calculated: log β1 = 8.5, log β2 = 15.6, log β3 = 22.5, log β4 = 25.7 for [CuCln]2-n and log β1 = 17.0, log β2 = 24.6, log β3 = 28.1, log β4 = 30.4 for [CuBrn]2-n. Structures of the studied complexes were optimized and electronic spectra were simulated using DFT and TD-DFT methodologies, respectively. According to the calculations, the more is the number of halide ligands the less is coordination number of copper ion.

Molecular vibrational investigation [FT-IR, FT-Raman, UV-Visible and NMR] on Bis(thiourea) Nickel chloride using HF and DFT calculations.

PubMed

Anand, S; Sundararajan, R S; Ramachandraraja, C; Ramalingam, S; Durga, R

2015-03-05

In the present research work, the FT-IR, FT-Raman spectra of the Bis(thiourea) Nickel chloride (BTNC) were recorded and analyzed. The observed fundamental frequencies in finger print and functional group regions were assigned according to their uniqueness region. The computational calculations were carried out by HF and DFT (B3LYP and B3PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets and the corresponding results were tabulated. The present organo-metallic compound was made up of covalent and coordination covalent bonds. The modified vibrational pattern of the complex molecule associated with ligand group was analyzed. Furthermore, the (13)C NMR and (1)H NMR spectral data were calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP/6-311++G(d,p) basis set and their spectra were simulated and the chemical shifts linked to TMS were compared. A investigation on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies were carried out. The kubo gap of the present compound was calculated related to HOMO and LUMO energies which confirm the occurring of charge transformation between the base and ligand. Besides frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) was performed. The NLO properties related to Polarizability and hyperpolarizability based on the finite-field approach were also discussed. Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.

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.

Adsorption of various types of amino acids on the graphene and boron-nitride nano-sheet, a DFT-D3 study

NASA Astrophysics Data System (ADS)

Zhiani, Rahele

2017-07-01

The binding properties of the adsorption of five different classes of amino acids, namely, alanine (Ala), arginine (Arg), asparagine (Asn), histidine (His) and cysteine (Cys) on the surface of the graphene (Gra) and the born-nitride (BN) nano-sheet structures were studied from molecular viewpoint using quantum mechanics methods. Density functional theory (DFT) and DFT-D3 calculations were carried out to investigate the electronic properties and the dispersion interaction of the amino acid/adsorbent complexes. Several parameters affecting the interactions between the amino acids and the adsorbent surfaces such as solvent effect, adsorption energy and separation distance were investigated. Findings show that Arg forms the most stable complexes with the graphene and the BN nano-sheet compare to the other amino acids used in this study. The observed frequency results which were related to the band gap energies were consistent with the above statement. Results exhibit that adsorption of the amino acids on the surface of the BN nano-sheet and the graphene accompanied with the release of the energy. Calculations show that there are no bonded interactions between the amino acids and adsorbent surfaces. The polarity of the BN nano-sheet provides the more affinity towards the amino acids. These results were proved by the quantum chemistry studies.

Photodissolution of ferrihydrite in the presence of oxalic acid: an in situ ATR-FTIR/DFT study.

PubMed

Bhandari, Narayan; Hausner, Douglas B; Kubicki, James D; Strongin, Daniel R

2010-11-02

The photodissolution of the iron oxyhydroxide, ferrihydrite, in the presence of oxalic acid was investigated with vibrational spectroscopy, density functional theory (DFT) calculations, and batch geochemical techniques that determined the composition of the solution phase during the dissolution process. Specifically, in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR- FTIR) was used to determine the structure of the adsorbed layer during the dissolution process at a solution pH of 4.5. DFT based computations were used to interpret the vibrational data associated with the surface monolayer in order to help determine the structure of the adsorbed complexes. Results showed that at pH 4.5, oxalate adsorbed on ferrihydrite adopted a mononuclear bidentate (MNBD) binding geometry. Photodissolution at pH 4.5 exhibited an induction period where the rate of Fe(II) release was limited by a low concentration of adsorbed oxalate due to the site-blocking of carbonate that was intrinsic to the surface of the ferrihydrite starting material. Oxalate displaced this initial carbonate over time, and the dissolution rate showed a corresponding increase. Irradiation of oxalate/ferrihydrite at pH 4.5 also ultimately led to the appearance of carbonate reaction product (distinct from carbonate intrinsic to the starting material) on the surface.

Structural investigation of α-LaZr2F11 by coupling X-ray powder diffraction, 19F solid state NMR and DFT calculations

NASA Astrophysics Data System (ADS)

Martineau, Charlotte; Legein, Christophe; Body, Monique; Péron, Olivier; Boulard, Brigitte; Fayon, Franck

2013-03-01

α-LaZr2F11 has been synthesized by solid state reaction. Its crystal structure has been refined from X-ray powder diffraction data (space group no. 72 Ibam, a=7.785(1) Å, b=10.086(1) Å and c=11.102(1) Å). α-LaZr2F11 contains one La, one Zr and four F inequivalent crystallographic sites. F3 and F4 are shared between one ZrF73- polyhedron and one LaF85- polyhedron, while F1 and F2 bridge two ZrF73- polyhedra. 19F 1D MAS NMR spectra of α-LaZr2F11 are in agreement with the proposed structural model. Assignment of the 19F resonances to the corresponding crystallographic sites has been performed on the basis of both their relative intensities and their correlation patterns in a 19F 2D dipolar-based double-quantum recoupling MAS NMR spectrum. DFT calculations of the 19F chemical shielding tensors have been performed using the GIPAW method implemented in the NMR-CASTEP code, for the experimental structure and two PBE-DFT geometry optimized structures of α-LaZr2F11 (atomic position optimization and full geometry optimization with rescaling of the unit cell volume to the experimental value). Computations were done with and without using a modified La pseudopotential allowing the treatment of the 4f localized empty orbitals of La3+. A relatively nice agreement between the experimental 19F isotropic and anisotropic chemical shifts and the values calculated for the proposed structural model is obtained.

Van der Waals corrected DFT study of adsorption of groups VA and VIA hydrides on graphene monoxide

NASA Astrophysics Data System (ADS)

Notash, M. Yaghoobi; Ebrahimzadeh, A. Rastkar

2016-06-01

Adsorption properties of H2O, H2S, NH3 and PH3 on graphene monoxide (GMO) nano flack are investigated using density functional theory (DFT). Calculations were carried out by van der Waals correction and general gradient approximation. The adsorption energies and charge transfer between species are obtained and discussed for the considered positions of adsorbate molecules. Charge transfer analysis show that the gas molecules act as an electron acceptor in all cases. The analysis of the adsorption energies suggest GMO can be a good candidate for the adsorption of these molecules.

A projection-free method for representing plane-wave DFT results in an atom-centered basis

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

Dunnington, Benjamin D.; Schmidt, J. R., E-mail: schmidt@chem.wisc.edu

2015-09-14

Plane wave density functional theory (DFT) is a powerful tool for gaining accurate, atomic level insight into bulk and surface structures. Yet, the delocalized nature of the plane wave basis set hinders the application of many powerful post-computation analysis approaches, many of which rely on localized atom-centered basis sets. Traditionally, this gap has been bridged via projection-based techniques from a plane wave to atom-centered basis. We instead propose an alternative projection-free approach utilizing direct calculation of matrix elements of the converged plane wave DFT Hamiltonian in an atom-centered basis. This projection-free approach yields a number of compelling advantages, including strictmore » orthonormality of the resulting bands without artificial band mixing and access to the Hamiltonian matrix elements, while faithfully preserving the underlying DFT band structure. The resulting atomic orbital representation of the Kohn-Sham wavefunction and Hamiltonian provides a gateway to a wide variety of analysis approaches. We demonstrate the utility of the approach for a diverse set of chemical systems and example analysis approaches.« less

A semi-blind logo watermarking scheme for color images by comparison and modification of DFT coefficients

NASA Astrophysics Data System (ADS)

Kusyk, Janusz; Eskicioglu, Ahmet M.

2005-10-01

Digital watermarking is considered to be a major technology for the protection of multimedia data. Some of the important applications are broadcast monitoring, copyright protection, and access control. In this paper, we present a semi-blind watermarking scheme for embedding a logo in color images using the DFT domain. After computing the DFT of the luminance layer of the cover image, the magnitudes of DFT coefficients are compared, and modified. A given watermark is embedded in three frequency bands: Low, middle, and high. Our experiments show that the watermarks extracted from the lower frequencies have the best visual quality for low pass filtering, adding Gaussian noise, JPEG compression, resizing, rotation, and scaling, and the watermarks extracted from the higher frequencies have the best visual quality for cropping, intensity adjustment, histogram equalization, and gamma correction. Extractions from the fragmented and translated image are identical to extractions from the unattacked watermarked image. The collusion and rewatermarking attacks do not provide the hacker with useful tools.

Experimental and DFT simulation study of a novel felodipine cocrystal: Characterization, dissolving properties and thermal decomposition kinetics.

PubMed

Yang, Caiqin; Guo, Wei; Lin, Yulong; Lin, Qianqian; Wang, Jiaojiao; Wang, Jing; Zeng, Yanli

2018-05-30

In this study, a new cocrystal of felodipine (Fel) and glutaric acid (Glu) with a high dissolution rate was developed using the solvent ultrasonic method. The prepared cocrystal was characterized using X-ray powder diffraction, differential scanning calorimetry, thermogravimetric (TG) analysis, and infrared (IR) spectroscopy. To provide basic information about the optimization of pharmaceutical preparations of Fel-based cocrystals, this work investigated the thermal decomposition kinetics of the Fel-Glu cocrystal through non-isothermal thermogravimetry. Density functional theory (DFT) simulations were also performed on the Fel monomer and the trimolecular cocrystal compound for exploring the mechanisms underlying hydrogen bonding formation and thermal decomposition. Combined results of IR spectroscopy and DFT simulation verified that the Fel-Glu cocrystal formed via the NH⋯OC and CO⋯HO hydrogen bonds between Fel and Glu at the ratio of 1:2. The TG/derivative TG curves indicated that the thermal decomposition of the Fel-Glu cocrystal underwent a two-step process. The apparent activation energy (E a ) and pre-exponential factor (A) of the thermal decomposition for the first stage were 84.90 kJ mol -1 and 7.03 × 10 7  min -1 , respectively. The mechanism underlying thermal decomposition possibly involved nucleation and growth, with the integral mechanism function G(α) of α 3/2 . DFT calculation revealed that the hydrogen bonding between Fel and Glu weakened the terminal methoxyl, methyl, and ethyl groups in the Fel molecule. As a result, these groups were lost along with the Glu molecule in the first thermal decomposition. In conclusion, the formed cocrystal exhibited different thermal decomposition kinetics and showed different E a , A, and shelf life from the intact active pharmaceutical ingredient. Copyright © 2018 Elsevier B.V. All rights reserved.

Simplified DFT methods for consistent structures and energies of large systems

NASA Astrophysics Data System (ADS)

Caldeweyher, Eike; Gerit Brandenburg, Jan

2018-05-01

Kohn–Sham density functional theory (DFT) is routinely used for the fast electronic structure computation of large systems and will most likely continue to be the method of choice for the generation of reliable geometries in the foreseeable future. Here, we present a hierarchy of simplified DFT methods designed for consistent structures and non-covalent interactions of large systems with particular focus on molecular crystals. The covered methods are a minimal basis set Hartree–Fock (HF-3c), a small basis set screened exchange hybrid functional (HSE-3c), and a generalized gradient approximated functional evaluated in a medium-sized basis set (B97-3c), all augmented with semi-classical correction potentials. We give an overview on the methods design, a comprehensive evaluation on established benchmark sets for geometries and lattice energies of molecular crystals, and highlight some realistic applications on large organic crystals with several hundreds of atoms in the primitive unit cell.

DFT/TD-DFT study on the electronic and spectroscopic properties of hollow cubic and hollow spherical (ZnO) m quantum dots interacting with CO, NO2 and SO3 molecules

NASA Astrophysics Data System (ADS)

Gopalakrishnan, Sankarasubramanian; Shankar, Ramasamy; Kolandaivel, Ponmalai

2018-03-01

Hollow spherical (HS) and hollow cubic (HC) (ZnO) m quantum dots (QDs) were constructed and optimized using density functional theory (DFT) method. CO, NO2 and SO3 molecules were used to interact with the HC and HS (ZnO) m QDs at the centre and on the surface of the QDs. The changes in the electronic energy levels of HC and HS (ZnO) m QDs due to the interactions of CO, NO2 and SO3 molecules have been studied. The electronic and spectroscopic properties, such as density of states, HOMO-LUMO energy gap, absorption spectra, IR and Raman spectra of HC and HS (ZnO) m QDs have been studied using DFT and Time dependent-DFT (TD-DFT) methods. The interaction energy values show that the SO3 molecule has strongly interacted with HC and HS (ZnO) m QDs than the CO and NO2 molecules. The results of the density of states show that the HC QDs have peaks that are very close to each other, whereas the same is found to be broad in the HS QDs. The HOMO-LUMO energy gap is more for the HS QDs than the HC QDs, and also it gets decreased, when the NO2 and SO3 molecules interact at the centre of the HC and HS (ZnO) m QDs. The blue and red shifts were observed in the absorption spectra of HS and HC QDs. The natural transition orbital (NTO) plot reveals that the interaction of the molecules on the surface of the QDs reduce the chance of electron-hole recombination; hence the energy gap increases for NO2 and SO3 molecular interactions on the surface of the HC and HS (ZnO) m QDs. The vibrational assignments have been made for HC and HS QDs interacting with CO, NO2 and SO3 molecules.

Thermal properties of black phosphorene and doped phosphorene (C, N & O): A DFT study

NASA Astrophysics Data System (ADS)

Devi, Anjna; Singh, Amarjeet

2018-04-01

In this work, we present the results from a DFT based computational study of pristine phosphorene and doped (C, N & O) phosphorene. We systematically investigated the lattice thermal properties of black phosphorene and the effect of doping on its thermal properties. We first determined the vibrational properties of pristine and doped phosphorene and from these results we calculated their thermal properties. We doped the phosphorene with C, N and O and observed that the structural stability of doped phosphorene decreases, while the thermal stability is increased as compared to pristine phosphorene. The presence of finite temperature effects in the doped system can contribute to acceleration of progress in future nano-scale technology.

The syntheses, molecular structure analyses and DFT studies on new benzil monohydrazone based Schiff bases

NASA Astrophysics Data System (ADS)

Elmacı, Gökhan; Duyar, Halil; Aydıner, Burcu; Seferoğlu, Nurgül; Naziri, Mir Abolfazl; Şahin, Ertan; Seferoğlu, Zeynel

2018-06-01

Benzil monohydrazone based Schiff bases were synthesized and characterized by 1H NMR, 13C NMR, HRMS as well as by single crystal X-ray diffraction. The geometries of the compounds was optimized by the DFT method and the results were compared with the X-ray diffraction data. The HOMO and LUMO energy gap and also related parameters (electronic chemical potential (μ) and global hardness (η), global electrophilicity index (ω) and softness (s)) were obtained from ground state calculations. In addition, the thermal properties of the compounds were investigated by DTA-TGA. The results showed that the compounds have good thermal properties for practical applications as optic dye.

Synthesis, structure characterization, photoluminescence properties and TD-DFT calculations for two new borates.

PubMed

Hadjadj, Nasreddine; Dems, Mohamed AbdEsselem; Merazig, Hocine; Bendjeddou, Lamia

2018-04-01

Due to their rich structural chemistry and wide variety of applications, borate materials have provided a rich area of research. In a continuation of this research, diethylammonium bis(2-oxidobenzoato-κ 2 O 1 ,O 2 )borate, C 4 H 12 N + ·BO 4 (C 7 H 4 O) 2 - , (1), and propylammonium bis(2-oxidobenzoato-κ 2 O 1 ,O 2 )borate, C 3 H 10 N + ·BO 4 (C 7 H 4 O) 2 - , (2), have been synthesized by the reaction of boric acid with salicylic acid under ambient conditions. In both structures, the B atom exhibits a slightly distorted tetrahedral environment formed by the bidentate coordination of two salicylate anions via the O atoms of the central carboxylate and oxide groups. In the crystals of salts (1) and (2), mixed cation-anion layers lying parallel to the (101) plane are formed through N-H...O, C-H...O and C-H...π/N-H...O hydrogen-bonding interactions, resulting, in each case, in a two-dimensional supramolecular architecture in the solid state. The photoluminescence properties of the salts were studied using the as-synthesized samples and reveal that salts (1) and (2) both display a strong blue-light emission, with maxima at 489 and 491 nm, respectively. In DFT/TD-DFT (time-dependent density functional theory) studies, the blue emission appears to be derived from an intramolecular charge transfer (ICT) excited state. In addition, IR and UV-Vis spectroscopies were used to investigate the title salts.

DFT+DMFT study of strain and interface effects in d1 and d2 t2 g-perovskites

NASA Astrophysics Data System (ADS)

Sclauzero, Gabriele; Dymkowski, Krzysztof; Ederer, Claude

2015-03-01

Metal-insulator transitions in thin films of early-transition metal correlated oxides are linked to both epitaxial strain and electronic reconstruction at the film/substrate interface. We separately address these two key factors for LaTiO3 and LaVO3 through density functional theory plus dynamical mean-field theory (DFT+DMFT). We find that mere epitaxial strain suffices to induce an insulator-to-metal transition in LaTiO3, but not in LaVO3, in agreement with recent experiments. We show that this difference can be explained by the combined effect of strain-induced changes in the crystal field splitting of t2 g orbitals and different orbital filling in these two materials. The role of the interface is investigated through DFT+DMFT simulations of LaVO3/SrTiO3 heterostructures with varying superlattice periodicities and substrate terminations. Our aim is to assess whether the metallicity observed at the LaVO3/SrTiO3 interface could be driven by pure electronic reconstruction effects, rather than structural or stoichiometric reasons (such as, e.g., O-related defects).

Spectroscopic and molecular structure investigation of the phosphorus-containing G‧2 dendrimer with terminal aldehyde groups using DFT method

NASA Astrophysics Data System (ADS)

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

2015-02-01

The FTIR and FT Raman spectra of the second generation dendrimer G‧2 built from thiophosphoryl core with terminal aldehyde groups have been recorded. The structural optimization and normal mode analysis were performed for model compound C, consisting of thiophosphoryl core, one branch with three repeated units, and four 4-oxybenzaldehyde terminal groups on the basis of the density functional theory (DFT) at the PBE/TZ2P level. The vibrational frequencies, infrared and Raman intensities for the t,g,g- and t,-g,g-conformers of the terminal groups were calculated. The t,g,g-conformer is 2.0 kcal/mol less stable compared to t,-g,g-conformer. A reliable assignment of the fundamental bands observed in the experimental IR and Raman spectra of dendrimer was achieved. For the low generations (G‧1 to G‧3) the disk form of studied dendrimer molecules is the most probable. For higher generations, the shape of dendrimer molecules will be that of a cauliflower.

Uranyl extraction by N,N-dialkylamide ligands studied using static and dynamic DFT simulations.

PubMed

Sieffert, Nicolas; Wipff, Georges

2015-02-14

We report DFT static and dynamic studies on uranyl complexes [UO(2)(NO(3))x(H(2)O)(y)L(z)](2-x) involved in the uranyl extraction from water to an "oil" phase (hexane) by an amide ligand L (N,N-dimethylacetamide). Static DFT results "in solution" (continuum SMD models for water and hexane) predict that the stepwise formation of [UO(2)(NO(3))(2)L(2)] from the UO(2)(H(2)O)(5)(2+) species is energetically favourable, and allow us to compare cis/trans isomers of penta- and hexa-coordinated complexes and key intermediates in the two solvents. DFT-MD simulations of [UO(2)(NO(3))(2)L(2)], [UO(2)(NO(3))(2)(H(2)O)L(2)], and [UO(2)(NO(3))(H(2)O)L(2)](+) species in explicit solvent environments (water, hexane, or the water/hexane interface) represented at the MM or full-DFT level reveal a versatile solvent dependent binding mode of nitrates, also evidenced by metadynamics simulations. In water and at the interface, the latter exchange from bi- to monodentate, via in plane rotational motions in some cases. Remarkably, structures of complexes at the interface are more "water-like" than gas phase- or hexane-like. Thus, the order of U-O(NO(3))/U-O(L) bond distances observed in the gas phase (U-O(nit) < U-OL) is inverted at the interface and in water. Overall, the results are consistent with the experimental observation of uranyl extraction from nitric acid solutions by amide analogues (bearing "fatty" substituents), and allow us to propose possible extraction mechanisms, involving complexation of L "right at the interface". They also point to the importance of the solvent environment and the dynamics on the structure and stability of the complexes.

Crystal structure, vibrational and DFT simulation studies of melaminium dihydrogen phosphite monohydrate

NASA Astrophysics Data System (ADS)

Arjunan, V.; Kalaivani, M.; Marchewka, M. K.; Mohan, S.

2013-08-01

The crystal structure investigations of melamine with phosphorous acid, namely melaminium dihydrogenphosphite monohydrate (C3N6H7·H2PO3·H2O) have been investigated by means of single crystal X-ray diffraction method. The title compound crystallizes in monoclinic crystal system, and the space group is P21/c with a = 10.069 Å, b = 21.592 Å, c = 12.409 Å and Z = 12. The vibrational assignments and analysis of melaminium dihydrogen phosphite monohydrate have also been performed by FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical simulations were performed with DFT (B3LYP) method using 6-31G**, cc-pVTZ, and 6-311++G** basis sets to determine the energy, structural, thermodynamic parameters and vibrational frequencies of melaminium dihydrogen phosphite monohydrate. The hydrogen atom from phosphorous acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak Osbnd H···O and Nsbnd H···O hydrogen bonds shows notable vibrational effects.

Analysis of the local structure around Cr3+ centers in perovskite KMgF3 using both ab initio (DFT) and semi-empirical (SPM) calculations

NASA Astrophysics Data System (ADS)

Emül, Y.; Erbahar, D.; Açıkgöz, M.

2014-11-01

The local structure around Cr3+ centers in perovskite KMgF3 crystal have been investigated through the applications of both an ab-initio, density functional theory (DFT), and a semi empirical, superposition model (SPM), analyses. A supercell approach is used for DFT calculations. All the tetragonal (Cr3+-VMg and Cr3+-Li+), trigonal (Cr3+-VK), and CrF5O cluster centers have been considered with various structural models based on the previously suggested experimental inferences. The significant structural changes around the Cr3+ centers induced by Mg2+ or K+ vacancies and the Li substitution at those vacancy sites have been determined and discussed by means of charge distribution. This study provides insight on both the roles of Mg2+ and K+ vacancies and Li+ ion in the local structural properties around Cr3+ centers in KMgF3.

Relativistic Zeroth-Order Regular Approximation Combined with Nonhybrid and Hybrid Density Functional Theory: Performance for NMR Indirect Nuclear Spin-Spin Coupling in Heavy Metal Compounds.

PubMed

Moncho, Salvador; Autschbach, Jochen

2010-01-12

A benchmark study for relativistic density functional calculations of NMR spin-spin coupling constants has been performed. The test set contained 47 complexes with heavy metal atoms (W, Pt, Hg, Tl, Pb) with a total of 88 coupling constants involving one or two heavy metal atoms. One-, two-, three-, and four-bond spin-spin couplings have been computed at different levels of theory (nonhybrid vs hybrid DFT, scalar vs two-component relativistic). The computational model was based on geometries fully optimized at the BP/TZP scalar relativistic zeroth-order regular approximation (ZORA) and the conductor-like screening model (COSMO) to include solvent effects. The NMR computations also employed the continuum solvent model. Computations in the gas phase were performed in order to assess the importance of the solvation model. The relative median deviations between various computational models and experiment were found to range between 13% and 21%, with the highest-level computational model (hybrid density functional computations including scalar plus spin-orbit relativistic effects, the COSMO solvent model, and a Gaussian finite-nucleus model) performing best.

Molecular interactions investigated with DFT calculations of QTAIM and NBO analyses: An application to dimeric structures of rice α-amylase/subtilisin inhibitor

NASA Astrophysics Data System (ADS)

Astani, Elahe K.; Hadipour, Nasser L.; Chen, Chun-Jung

2017-03-01

Characterization of the dimer interactions at the dimeric interface of the crystal structure of rice α-amylase/subtilisin inhibitor (RASI) were performed using the quantum theory of atoms in molecules (QTAIM) and natural bonding orbital (NBO) analyses at the density-functional theory (DFT) level. The results revealed that Gly27 and Arg151 of chain A are the main residues involved in hydrogen bonds, dipole-dipole, and charge-dipole interactions with Gly64, Ala66, Ala67 and Arg81 of chain B at the dimeric interface. Calcium ion of chain A plays the significant role in the stability of the dimeric structure through a strong charge-charge interaction with Ala66.

FT-IR, Laser-Raman spectra and quantum chemical calculations of methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate-A DFT approach.

PubMed

Sert, Yusuf; Sreenivasa, S; Doğan, H; Manojkumar, K E; Suchetan, P A; Ucun, Fatih

2014-06-05

In this study the experimental and theoretical vibrational frequencies of a newly synthesized anti-tumor and anti-inflammatory agent namely, methyl 4-(trifluoromethyl)-1H-pyrrole-3-carboxylate 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, bond angles and torsion angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr and DFT/M06-2X: highly parameterized, 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. Copyright © 2014 Elsevier B.V. All rights reserved.

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.

A DFT Study of Pyrrole-Isoxazole Derivatives as Chemosensors for Fluoride Anion

PubMed Central

Jin, Ruifa; Sun, Weidong; Tang, Shanshan

2012-01-01

The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F− Cl−, Br−, AcO−, and H2PO4−) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F− is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only. PMID:23109833

Spectroscopic studies and quantum chemical investigations of (3,4-dimethoxybenzylidene) propanedinitrile.

PubMed

Gupta, Ujval; Kumar, Vinay; Singh, Vivek K; Kant, Rajni; Khajuria, Yugal

2015-04-05

The Fourier Transform Infrared (FTIR), Ultra-Violet Visible (UV-Vis) spectroscopy and Thermogravimetric (TG) analysis of (3,4-dimethoxybenzylidene) propanedinitrile have been carried out and investigated using quantum chemical calculations. The molecular geometry, harmonic vibrational frequencies, Mulliken charges, natural atomic charges and thermodynamic properties in the ground state have been investigated by using Hartree Fock Theory (HF) and Density Functional Theory (DFT) using B3LYP functional with 6-311G(d,p) basis set. Both HF and DFT methods yield good agreement with the experimental data. Vibrational modes are assigned with the help of Vibrational Energy Distribution Analysis (VEDA) program. UV-Visible spectrum was recorded in the spectral range of 190-800nm and the results are compared with the calculated values using TD-DFT approach. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results obtained from the studies of Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) are used to calculate molecular parameters like ionization potential, electron affinity, global hardness, electron chemical potential and global electrophilicity. Copyright © 2014 Elsevier B.V. All rights reserved.

The study of intermolecular interactions in NLO crystal melaminium chloride hemihydrate using DFT simulation and Hirshfeld surface analysis

NASA Astrophysics Data System (ADS)

Sangeetha, K.; Kumar, V. R. Suresh; Marchewka, M. K.; Binoy, J.

2018-05-01

Since, the intermolecular interactions play a crucial role in the formation of crystalline network, its analysis throws light on structure dependent crystalline properties. In the present study, DFT based vibrational spectral investigation has been performed in the stretching region (3500 cm-1 - 2800 cm-1) of IR and Raman spectra of melaminium chloride hemihydrates. The intermolecular interaction has been investigated by analyzing the half width of the OH and NH stretching profile of the deconvoluted spectra. Correlation of vibrational spectra with Hirshfeld surface analysis and finger print plot has been contemplated and molecular docking studies has been performed on melaminium chloride hemihydrate to assess its role in the drug transport mechanism and toxicity to human body.

The Hubbard Dimer: A Complete DFT Solution to a Many-Body Problem

NASA Astrophysics Data System (ADS)

Smith, Justin; Carrascal, Diego; Ferrer, Jaime; Burke, Kieron

2015-03-01

In this work we explain the relationship between density functional theory and strongly correlated models using the simplest possible example, the two-site asymmetric Hubbard model. We discuss the connection between the lattice and real-space and how this is a simple model for stretched H2. We can solve this elementary example analytically, and with that we can illuminate the underlying logic and aims of DFT. While the many-body solution is analytic, the density functional is given only implicitly. We overcome this difficulty by creating a highly accurate parameterization of the exact function. We use this parameterization to perform benchmark calculations of correlation kinetic energy, the adiabatic connection, etc. We also test Hartree-Fock and the Bethe Ansatz Local Density Approximation. We also discuss and illustrate the derivative discontinuity in the exchange-correlation energy and the infamous gap problem in DFT. DGE-1321846, DE-FG02-08ER46496.

Spectral investigations and DFT studies of 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione (caffeine) interaction and recognition by single amino acid derived self-assembled nanostructures

NASA Astrophysics Data System (ADS)

Govindhan, R.; Karthikeyan, B.

2018-03-01

Recognition of xanthine alkaloid caffeine with 3,5-bis(trifluoromethyl)benzylamine derived peptide nanotubes (BTTPNTs) through chemical interaction have been achieved through the host-guest like interaction. DFT simulation is carried out for caffeine interacted with BTTPNTs system and also experimentally characterized by ultraviolet-visible (UV-vis) absorbance, confocal Raman spectra (CRS) with microscopic imaging (CRM), FT-Raman, surface enhanced Raman scattering (SERS), UV-diffuse reflectance spectra (UV-DRS), high resolution transmission electron microscopy (HR-TEM) and cyclic voltammetry (CV) studies. The results are used to examine the morphologies, size of the nanostructure and study of its interaction with the caffeine molecule. The results show that BTTPNTs is having potential for sensing the caffeine molecules through the binding occurred from the NH2 of tyrosine moiety of the BTTPNTs. This intermolecular association through face-to-face stacking of BTTPNTs is explained by detailed DFT calculations.

Block-localized wavefunction (BLW) method at the density functional theory (DFT) level.

PubMed

Mo, Yirong; Song, Lingchun; Lin, Yuchun

2007-08-30

The block-localized wavefunction (BLW) approach is an ab initio valence bond (VB) method incorporating the efficiency of molecular orbital (MO) theory. It can generate the wavefunction for a resonance structure or diabatic state self-consistently by partitioning the overall electrons and primitive orbitals into several subgroups and expanding each block-localized molecular orbital in only one subspace. Although block-localized molecular orbitals in the same subspace are constrained to be orthogonal (a feature of MO theory), orbitals between different subspaces are generally nonorthogonal (a feature of VB theory). The BLW method is particularly useful in the quantification of the electron delocalization (resonance) effect within a molecule and the charge-transfer effect between molecules. In this paper, we extend the BLW method to the density functional theory (DFT) level and implement the BLW-DFT method to the quantum mechanical software GAMESS. Test applications to the pi conjugation in the planar allyl radical and ions with the basis sets of 6-31G(d), 6-31+G(d), 6-311+G(d,p), and cc-pVTZ show that the basis set dependency is insignificant. In addition, the BLW-DFT method can also be used to elucidate the nature of intermolecular interactions. Examples of pi-cation interactions and solute-solvent interactions will be presented and discussed. By expressing each diabatic state with one BLW, the BLW method can be further used to study chemical reactions and electron-transfer processes whose potential energy surfaces are typically described by two or more diabatic states.

Dispersion interactions with linear scaling DFT: a study of planar molecules on charged polar surfaces

NASA Astrophysics Data System (ADS)

Andrinopoulos, Lampros; Hine, Nicholas; Haynes, Peter; Mostofi, Arash

2010-03-01

The placement of organic molecules such as CuPc (copper phthalocyanine) on wurtzite ZnO (zinc oxide) charged surfaces has been proposed as a way of creating photovoltaic solar cellsfootnotetextG.D. Sharma et al., Solar Energy Materials & Solar Cells 90, 933 (2006) ; optimising their performance may be aided by computational simulation. Electronic structure calculations provide high accuracy at modest computational cost but two challenges are encountered for such layered systems. First, the system size is at or beyond the limit of traditional cubic-scaling Density Functional Theory (DFT). Second, traditional exchange-correlation functionals do not account for van der Waals (vdW) interactions, crucial for determining the structure of weakly bonded systems. We present an implementation of recently developed approachesfootnotetextP.L. Silvestrelli, P.R.L. 100, 102 (2008) to include vdW in DFT within ONETEPfootnotetextC.-K. Skylaris, P.D. Haynes, A.A. Mostofi and M.C. Payne, J.C.P. 122, 084119 (2005) , a linear-scaling package for performing DFT calculations using a basis of localised functions. We have applied this methodology to simple planar organic molecules, such as benzene and pentacene, on ZnO surfaces.

Electronic structure and optical properties of noncentrosymmetric LiGaSe2: Experimental measurements and DFT band structure calculations

NASA Astrophysics Data System (ADS)

Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.

2017-04-01

We report on measurements of X-ray photoelectron (XP) spectra for pristine and Ar+ ion-irradiated surfaces of LiGaSe2 single crystal grown by Bridgman-Stockbarger method. Electronic structure of the LiGaSe2 compound is studied from a theoretical and experimental viewpoint. In particular, total and partial densities of states of LiGaSe2 are investigated by density functional theory (DFT) calculations employing the augmented plane wave + local orbitals (APW + lo) method and they are verified by data of X-ray spectroscopy measurements. The DFT calculations indicate that the main contributors to the valence band of LiGaSe2 are the Se 4p states, which contribute mainly at the top and in the upper portion of the valence band, with also essential contributions of these states in the lower portion of the band. Other substantial contributions to the valence band of LiGaSe2 emerge from the Ga 4s and Ga 4p states contributing mainly at the lower ant upper portions of the valence band, respectively. With respect to the conduction band, the calculations indicate that its bottom is composed mainly from contributions of the unoccupied Ga s and Se p states. The present calculations are confirmed experimentally when comparing the XP valence-band spectrum of the LiGaS2 single crystal on a common energy scale with the X-ray emission bands representing the energy distribution of the Ga 4p and Se 4p states. Measurements of the fundamental absorption edges at room temperature reveal that bandgap value, Eg, of LiGaSe2 is equal to 3.47 eV and the Eg value increases up to 3.66 eV when decreasing temperature to 80 K. The main optical characteristics of the LiGaSe2 compound are clarified by the DFT calculations.

First principles investigation of structural, vibrational and thermal properties of black and blue phosphorene

NASA Astrophysics Data System (ADS)

Arif Khalil, R. M.; Ahmad, Javed; Rana, Anwar Manzoor; Bukhari, Syed Hamad; Tufiq Jamil, M.; Tehreem, Tuba; Nissar, Umair

2018-05-01

In this investigation, structural, dynamical and thermal properties of black and blue phosphorene (P) are presented through the first principles calculations based on the density functional theory (DFT). These DFT calculations depict that due to the approximately same values of ground state energy at zero Kelvin and Helmholtz free energy at room-temperature, it is expected that both structures can coexist at transition temperature. Lattice dynamics of both phases were investigated by using the finite displacement supercell approach. It is noticed on the basis of harmonic approximation thermodynamic calculations that the blue phase is thermodynamically more stable than the black phase above 155 K.

DFT investigations on mechanical stability, electronic structure and magnetism in Co2TaZ (Z = Al, Ga, In) heusler alloys

NASA Astrophysics Data System (ADS)

Khandy, Shakeel Ahmad; Gupta, Dinesh C.

2017-12-01

Ferromagnetic Heusler compounds have vast and imminent applications for novel devices, smart materials thanks to density functional theory (DFT) based simulations, which have scored out a new approach to study these materials. We forecast the structural stability of Co2TaZ alloys on the basis of total energy calculations and mechanical stability criteria. The elastic constants, robust spin-polarized ferromagnetism and electron densities in these half-metallic alloys are also discussed. The observed structural aspects calculated to predict the stability and equilibrium lattice parameters agree well with the experimental results. The elastic parameters like elastic constants, bulk, Young’s and shear moduli, poison’s and Pugh ratios, melting temperatures, etc have been put together to establish their mechanical properties. The elaborated electronic band structures along with indirect band gaps and spin polarization favour the application of these materials in spintronics and memory device technology.

Methanol Synthesis from CO2 Hydrogenation over a Pd4/In2O3 Model Catalyst: A Combined DFT and Kinetic Study

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

Ye, Jingyun; Liu, Changjun; Mei, Donghai

2014-08-01

Methanol synthesis from CO2 hydrogenation on Pd4/In2O3 has been investigated using density functional theory (DFT) and microkinetic modeling. In this study, three possible routes in the reaction network of CO2 + H2 → CH3OH + H2O have been examined. Our DFT results show that the HCOO route competes with the RWGS route whereas a high activation barrier kinetically blocks the HCOOH route. DFT results also suggest that H2COO* + H* ↔ H2CO* +OH* and cis-COOH* + H* ↔CO* + H2O* are the rate limiting steps in the HCOO route and the RWGS route, respectively. Microkinetic modeling results demonstrate that themore » HCOO route is the dominant reaction route for methanol synthesis from CO2 hydrogenation. We found that the activation of H adatom on the small Pd cluster and the presence of H2O on the In2O3 substrate play important roles in promoting the methanol synthesis. The hydroxyl adsorbed at the interface of Pd4/In2O3 induces the transformation of the supported Pd4 cluster from a butterfly structure into a tetrahedron structure. This important structure change not only indicates the dynamical nature of the supported nanoparticle catalyst structure during the reaction but also shifts the final hydrogenation step from H2COH to CH3O.« less

Mutual effects of copper and phosphate on their interaction with γ-Al2O3: combined batch macroscopic experiments with DFT calculations.

PubMed

Ren, Xuemei; Yang, Shitong; Tan, Xiaoli; Chen, Changlun; Sheng, Guodong; Wang, Xiangke

2012-10-30

The mutual effects of Cu(II) and phosphate on their interaction with γ-Al(2)O(3) are investigated by using batch experiments combined with density functional theory (DFT) calculations. The results of batch experiments show that coexisting phosphate promotes the retention of Cu(II) on γ-Al(2)O(3), whereas phosphate retention is not affected by coexisting Cu(II) at low initial phosphate concentrations (≤ 3.6 mg P/L). Cu-phosphate aqueous complexes control Cu(II) retention through the formation of type B ternary surface complexes (where phosphate bridges γ-Al(2)O(3) and Cu(II)) at pH 5.5. This deduction is further supported by the results of DFT calculations. More specifically, the DFT calculation results indicate that the type B ternary surface complexes prefer to form outer-sphere or monodentate inner-sphere binding mode under our experimental conditions. The enhancement of phosphate retention on γ-Al(2)O(3) in the presence of Cu(II) at high initial phosphate concentrations (>3.6 mg P/L) may be attributed to the formation of 1:2 Cu(II)-phosphate species and/or surface precipitates. Understanding the mutual effects of phosphate and Cu(II) on their mobility and transport in mineral/water environments is more realistic to design effective remediation strategies for reducing their negative impacts on aquatic/terrestrial environments. Copyright © 2012 Elsevier B.V. All rights reserved.

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.

Advantages of GPU technology in DFT calculations of intercalated graphene

NASA Astrophysics Data System (ADS)

Pešić, J.; Gajić, R.

2014-09-01

Over the past few years, the expansion of general-purpose graphic-processing unit (GPGPU) technology has had a great impact on computational science. GPGPU is the utilization of a graphics-processing unit (GPU) to perform calculations in applications usually handled by the central processing unit (CPU). Use of GPGPUs as a way to increase computational power in the material sciences has significantly decreased computational costs in already highly demanding calculations. A level of the acceleration and parallelization depends on the problem itself. Some problems can benefit from GPU acceleration and parallelization, such as the finite-difference time-domain algorithm (FTDT) and density-functional theory (DFT), while others cannot take advantage of these modern technologies. A number of GPU-supported applications had emerged in the past several years (www.nvidia.com/object/gpu-applications.html). Quantum Espresso (QE) is reported as an integrated suite of open source computer codes for electronic-structure calculations and materials modeling at the nano-scale. It is based on DFT, the use of a plane-waves basis and a pseudopotential approach. Since the QE 5.0 version, it has been implemented as a plug-in component for standard QE packages that allows exploiting the capabilities of Nvidia GPU graphic cards (www.qe-forge.org/gf/proj). In this study, we have examined the impact of the usage of GPU acceleration and parallelization on the numerical performance of DFT calculations. Graphene has been attracting attention worldwide and has already shown some remarkable properties. We have studied an intercalated graphene, using the QE package PHonon, which employs GPU. The term ‘intercalation’ refers to a process whereby foreign adatoms are inserted onto a graphene lattice. In addition, by intercalating different atoms between graphene layers, it is possible to tune their physical properties. Our experiments have shown there are benefits from using GPUs, and we reached an

Stages of Se adsorption on Au(111): A combined XPS, LEED, TOF-DRS, and DFT study

NASA Astrophysics Data System (ADS)

Ruano, G.; Tosi, E.; Sanchez, E.; Abufager, P.; Martiarena, M. L.; Grizzi, O.; Zampieri, G.

2017-08-01

We have studied the adsorption of Se on the surface Au(111) using XPS, TOF-DRS, LEED and DFT calculations. The use of a doser that operates in vacuum allowed us to investigate all the stages of the adsorption from the clean surface up to the formation of multilayers. In the monolayer regime we have found two ordered phases with distinctive LEED patterns. The LEED pattern of the first phase presents three fractional spots arranged symmetrically around the positions of the spots in a √3x√3 pattern. The analysis of this pattern suggests the formation of either a nxn superstructure of √3x√3 domains with n=19 or n=22, or that the adsorption occurs without removing the 22x√3 herringbone reconstruction of the gold surface. This last possibility is in accordance with DFT calculations which show that the charge transfer to a Se adsorbate might not be enough to destabilize the surface reconstruction. Increasing the coverage, beyond 0.3 ML a new LEED pattern appears with broad spots which upon annealing at 150 °C become well defined indicating a 1×8 periodicity. At the highest doses we have observed the formation of multilayers with no discernible LEED pattern. The comparison with adsorption experiments carried out in liquid solutions show similarities and also some important differences.

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

Elucidating the mass spectrum of the retronecine alkaloid using DFT calculations.

PubMed

Modesto-Costa, Lucas; Martinez, Sabrina T; Pinto, Angelo C; Vessecchi, Ricardo; Borges, Itamar

2018-06-23

Pyrrolizidine alkaloids are natural molecules playing important roles in different biochemical processes in nature and in humans. In this work, the electron ionization mass spectrum (EI-MS) of retronecine, an alkaloid molecule found in plants, is investigated computationally. Its mass spectrum can be characterized by three main fragment ions having the following m/z ratios: 111, 94 and 80. In order to rationalize the mass spectrum, minima and transition state geometries were computed using density functional theory (DFT). It was showed that the dissociation process includes an aromatization of the originally five-membered ring of retronecine converted into a six-membered ring compound. A fragmentation pathway mechanism involving dissociation activation barriers that are easily overcome by the initial ionization energy was found. From the computed quantum chemical geometric, atomic charges and energetic parameters, the abundance of each ion in the mass spectrum of retronecine was discussed. This article is protected by copyright. All rights reserved.

Chlorophenol sorption on multi-walled carbon nanotubes: DFT modeling and structure-property relationship analysis.

PubMed

Watkins, Marquita; Sizochenko, Natalia; Moore, Quentarius; Golebiowski, Marek; Leszczynska, Danuta; Leszczynski, Jerzy

2017-02-01

The presence of chlorophenols in drinking water can be hazardous to human health. Understanding the mechanisms of adsorption under specific experimental conditions would be beneficial when developing methods to remove toxic substances from drinking water during water treatment in order to limit human exposure to these contaminants. In this study, we investigated the sorption of chlorophenols on multi-walled carbon nanotubes using a density functional theory (DFT) approach. This was applied to study selected interactions between six solvents, five types of nanotubes, and six chlorophenols. Experimental data were used to construct structure-adsorption relationship (SAR) models that describe the recovery process. Specific interactions between solvents and chlorophenols were taken into account in the calculations by using novel specific mixture descriptors.

Relationship between electronic properties and drug activity of seven quinoxaline compounds: A DFT study

NASA Astrophysics Data System (ADS)

Behzadi, Hadi; Roonasi, Payman; Assle taghipour, Khatoon; van der Spoel, David; Manzetti, Sergio

2015-07-01

The quantum chemical calculations at the DFT/B3LYP level of theory were carried out on seven quinoxaline compounds, which have been synthesized as anti-Mycobacterium tuberculosis agents. Three conformers were optimized for each compound and the lowest energy structure was found and used in further calculations. The electronic properties including EHOMO, ELUMO and related parameters as well as electron density around oxygen and nitrogen atoms were calculated for each compound. The relationship between the calculated electronic parameters and biological activity of the studied compounds were investigated. Six similar quinoxaline derivatives with possible more drug activity were suggested based on the calculated electronic descriptors. A mechanism was proposed and discussed based on the calculated electronic parameters and bond dissociation energies.

Arsenic incorporation into FeS 2 pyrite and its influence on dissolution: A DFT study

NASA Astrophysics Data System (ADS)

Blanchard, Marc; Alfredsson, Maria; Brodholt, John; Wright, Kate; Catlow, C. Richard A.

2007-02-01

FeS 2 pyrite can incorporate large amounts of arsenic (up to ca. 10 wt%) and hence has a strong impact on the mobility of this toxic metalloid. Focussing on the lowest arsenic concentrations for which the incorporation occurs in solid solution, the substitution mechanisms involved have been investigated by assuming simple incorporation reactions in both oxidising and reducing conditions. The solution energies were calculated by Density Functional Theory (DFT) calculations and we predict that the formation of AsS dianion groups is the most energetically favourable mechanism. The results also suggest that the presence of arsenic will accelerate the dissolution and thus the generation of acid drainage, when the crystal dissolves in oxidising conditions.

Spectroscopic and DFT Study of RhIII Chloro Complex Transformation in Alkaline Solutions.

PubMed

Vasilchenko, Danila B; Berdyugin, Semen N; Korenev, Sergey V; O'Kennedy, Sean; Gerber, Wilhelmus J

2017-09-05

The hydrolysis of [RhCl 6 ] 3- in NaOH-water solutions was studied by spectrophotometric methods. The reaction proceeds via successive substitution of chloride with hydroxide to quantitatively form [Rh(OH) 6 ] 3- . Ligand substitution kinetics was studied in an aqueous 0.434-1.085 M NaOH matrix in the temperature range 5.5-15.3 °C. Transformation of [RhCl 6 ] 3- into [RhCl 5 (OH)] 3- was found to be the rate-determining step with activation parameters of ΔH † = 105 ± 4 kJ mol -1 and ΔS † = 59 ± 10 J K -1 mol -1 . The coordinated hydroxo ligand(s) induces rapid ligand substitution to form [Rh(OH) 6 ] 3- . By simulating ligand substitution as a dissociative mechanism, using density functional theory (DFT), we can now explain the relatively fast and slow kinetics of chloride substitution in basic and acidic matrices, respectively. Moreover, the DFT calculated activation energies corroborated experimental data that the kinetic stereochemical sequence of [RhCl 6 ] 3- hydrolysis in an acidic solution proceeds as [RhCl 6 ] 3- → [RhCl 5 (H 2 O)] 2- → cis-[RhCl 4 (H 2 O) 2 ] - . However, DFT calculations predict in a basic solution the trans route of substitution [RhCl 6 ] 3- → [RhCl 5 (OH)] 3- → trans-[RhCl 4 (OH) 2 ] 3- is kinetically favored.

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, 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.

Modelling realistic TiO2 nanospheres: A benchmark study of SCC-DFTB against hybrid DFT

NASA Astrophysics Data System (ADS)

Selli, Daniele; Fazio, Gianluca; Di Valentin, Cristiana

2017-10-01

TiO2 nanoparticles (NPs) are nowadays considered fundamental building blocks for many technological applications. Morphology is found to play a key role with spherical NPs presenting higher binding properties and chemical activity. From the experimental point of view, the characterization of these nano-objects is extremely complex, opening a large room for computational investigations. In this work, TiO2 spherical NPs of different sizes (from 300 to 4000 atoms) have been studied with a two-scale computational approach. Global optimization to obtain stable and equilibrated nanospheres was performed with a self-consistent charge density functional tight-binding (SCC-DFTB) simulated annealing process, causing a considerable atomic rearrangement within the nanospheres. Those SCC-DFTB relaxed structures have been then optimized at the DFT(B3LYP) level of theory. We present a systematic and comparative SCC-DFTB vs DFT(B3LYP) study of the structural properties, with particular emphasis on the surface-to-bulk sites ratio, coordination distribution of surface sites, and surface energy. From the electronic point of view, we compare HOMO-LUMO and Kohn-Sham gaps, total and projected density of states. Overall, the comparisons between DFTB and hybrid density functional theory show that DFTB provides a rather accurate geometrical and electronic description of these nanospheres of realistic size (up to a diameter of 4.4 nm) at an extremely reduced computational cost. This opens for new challenges in simulations of very large systems and more extended molecular dynamics.

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.

Using the DFT-D method to describe dispersion interactions in systems of weakly-bonded Xe-aromatic molecules

NASA Astrophysics Data System (ADS)

Andriichenko, N. N.; Ermilov, A. Yu.

2013-08-01

The optimum version of the DFT-D class of methods (BHHLYP-D2, 6-31G*) is chosen to describe binding in a Xe-phenol system with the aim of subsequent KM/MM calculations for complex Xe-containing protein systems. It is shown that the stability of the Xe-phenol system is due to weak dispersion interactions not described in conventional approaches using the density functional. The MP2 approach using the (aug)-cc-pVTZ basis and Stuttgart pseudopotential, which yield the best reproduction of the characteristics of a Xe2 xenon dimer, is chosen as the reference standard. It is noted that the 2010 DFT-D3 methods underestimate the binding energy by a factor of nearly three, while DFT methods without dispersion corrections do not reproduce the stability of Xe2 and Xe-phenol systems. It is found that in the best version of calculations, BHHLYP-D2, the binding energy in Xe-phenol complex is estimated to be 2.7 kcal/mol versus the 3.1 kcal/mol found using the comparative approach. It is concluded that BHHLYP-D2 adequately reproduces the difference between the two conformers of the Xe-phenol complex and trend toward an increase in binding energy in the series of aromatic amino acids (phenylalanine, tyrosine, and tryptophan). DFT-D can also indicate the existence of excess conformers that are missing in systems according to more precise descriptions (MP2/(aug)-cc-pVTZ).

Spectral analysis of the Earth's topographic potential via 2D-DFT: a new data-based degree variance model to degree 90,000

NASA Astrophysics Data System (ADS)

Rexer, Moritz; Hirt, Christian

2015-09-01

Classical degree variance models (such as Kaula's rule or the Tscherning-Rapp model) often rely on low-resolution gravity data and so are subject to extrapolation when used to describe the decay of the gravity field at short spatial scales. This paper presents a new degree variance model based on the recently published GGMplus near-global land areas 220 m resolution gravity maps (Geophys Res Lett 40(16):4279-4283, 2013). We investigate and use a 2D-DFT (discrete Fourier transform) approach to transform GGMplus gravity grids into degree variances. The method is described in detail and its approximation errors are studied using closed-loop experiments. Focus is placed on tiling, azimuth averaging, and windowing effects in the 2D-DFT method and on analytical fitting of degree variances. Approximation errors of the 2D-DFT procedure on the (spherical harmonic) degree variance are found to be at the 10-20 % level. The importance of the reference surface (sphere, ellipsoid or topography) of the gravity data for correct interpretation of degree variance spectra is highlighted. The effect of the underlying mass arrangement (spherical or ellipsoidal approximation) on the degree variances is found to be crucial at short spatial scales. A rule-of-thumb for transformation of spectra between spherical and ellipsoidal approximation is derived. Application of the 2D-DFT on GGMplus gravity maps yields a new degree variance model to degree 90,000. The model is supported by GRACE, GOCE, EGM2008 and forward-modelled gravity at 3 billion land points over all land areas within the SRTM data coverage and provides gravity signal variances at the surface of the topography. The model yields omission errors of 9 mGal for gravity (1.5 cm for geoid effects) at scales of 10 km, 4 mGal (1 mm) at 2-km scales, and 2 mGal (0.2 mm) at 1-km scales.

Solid state structural investigations of the bis(chalcone) compound with single crystal X-ray crystallography, DFT, gamma-ray spectroscopy and chemical spectroscopy methods

NASA Astrophysics Data System (ADS)

Yakalı, Gül; Biçer, Abdullah; Eke, Canel; Cin, Günseli Turgut

2018-04-01

A bis(chalcone), (2E,6E)-2,6-bis((E)-3phenylallidene)cyclohexanone, was characterized by 1H NMR, 13C NMR, FTIR, UV-Vis spectroscopy, gamma-ray spectroscopy and single crystal X- ray structural analysis. The optimized molecular structure of the compound is calculated using DFT/B3LYP with 6-31G (d,p) level. The calculated geometrical parameters are in good agreement with the experimental data obtained from our reported X-ray structure. The powder and single crystal compounds were gama-irradiated using clinical electron linear accelerator and 60Co gamma-ray source, respectively. Spectral studies (1H NMR, 13C NMR, FTIR and UV-Vis) of powder chalcone compound were also investigated before and after irradiation. Depending on the irradiation notable changes were observed in spectral features powder sample. Single crystal X-ray diffraction investigation shows that both unirradiated and irradiated single crystal samples crystallizes in a orthorhombic crystal system in the centrosymmetric space group Pbcn and exhibits an C-H..O intramolecular and intermolecular hydrogen bonds. The crystal packing is stabilised by strong intermolecular bifurcate C-H..O hydrogen bonds and π…π stacking interactions. The asymmetric unit of the title compound contains one-half of a molecule. The other half of the molecule is generated with (1-x,y,-3/2-z) symmetry operator. The molecule is almost planar due to having π conjugated system of chalcones. However, irradiated single crystal compound showed significant changes lattice parameters, crystal volume and density. According to results of gamma-ray spectroscopy, radioactive elements of powder compound which are 123Sb(n,g),124Sb,57Fe(g,p),56Mn, 55Mn(g,n), and 54Mn were determined using photoactivation analysis. However, the most intensive gamma-ray energy signals are 124Sb.

From Mahan excitons to Landau levels at high magnetic fields: 2DFT spectroscopy reveals hidden quantum correlations (Conference Presentation)

NASA Astrophysics Data System (ADS)

Karaiskaj, Denis

2017-02-01

Two-dimensional electron gases have been the subject of research for decades. Modulation doped GaAs quantum wells in the absence of magnetic fields exhibit interesting many-body physics such as the Fermi edge singularity or Mahan exciton and can be regarded as a collective excitation of the system. Under high magnetic fields Landau levels form which have been studied using transport and optical measurements. Nonlinear coherent two-dimensional Fourier transform (2DFT) spectroscopy however provides new insights into these systems. We present the 2DFT spectra of Mahan Excitons associated with the heavy-hole and light-hole resonances observed in a modulation doped GaAs/AlGaAs single quantum well [1]. These resonances are observed to be strongly coupled through many-body interactions. The 2DFT spectra were measured using co-linear, cross-linear, and co-circular polarizations and reveal striking differences. Furthermore, 2DFT spectra at high magnetic fields performed at the National High Magnetic Field Lab (NHMFL) in Tallahassee, Florida will be discussed. The spectra exhibit new features and peculiar line shapes suggesting interesting underlying physics. [1] J. Paul, C. E. Stevens, C. Liu, P. Dey, C. McIntyre, V. Turkowski, J. L. Reno, D. J. Hilton, and D. Karaiskaj, Phys. Rev. Lett.116, 157401 (2016).

A DFT-Based Computational-Experimental Methodology for Synthetic Chemistry: Example of Application to the Catalytic Opening of Epoxides by Titanocene.

PubMed

Jaraíz, Martín; Enríquez, Lourdes; Pinacho, Ruth; Rubio, José E; Lesarri, Alberto; López-Pérez, José L

2017-04-07

A novel DFT-based Reaction Kinetics (DFT-RK) simulation approach, employed in combination with real-time data from reaction monitoring instrumentation (like UV-vis, FTIR, Raman, and 2D NMR benchtop spectrometers), is shown to provide a detailed methodology for the analysis and design of complex synthetic chemistry schemes. As an example, it is applied to the opening of epoxides by titanocene in THF, a catalytic system with abundant experimental data available. Through a DFT-RK analysis of real-time IR data, we have developed a comprehensive mechanistic model that opens new perspectives to understand previous experiments. Although derived specifically from the opening of epoxides, the prediction capabilities of the model, built on elementary reactions, together with its practical side (reaction kinetics simulations of real experimental conditions) make it a useful simulation tool for the design of new experiments, as well as for the conception and development of improved versions of the reagents. From the perspective of the methodology employed, because both the computational (DFT-RK) and the experimental (spectroscopic data) components can follow the time evolution of several species simultaneously, it is expected to provide a helpful tool for the study of complex systems in synthetic chemistry.

Scavenging performance and antioxidant activity of γ-alumina nanoparticles towards DPPH free radical: Spectroscopic and DFT-D studies.

PubMed

Zamani, Mehdi; Moradi Delfani, Ali; Jabbari, Morteza

2018-05-03

The radical scavenging performance and antioxidant activity of γ-alumina nanoparticles towards 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical were investigated by spectroscopic and computational methods. The radical scavenging ability of γ-alumina nanoparticles in the media with different polarity (i.e. i-propanol and n-hexane) was evaluated by measuring the DPPH absorbance in UV-Vis absorption spectra. The structure and morphology of γ-alumina nanoparticles before and after adsorption of DPPH were studied using XRD, FT-IR and UV-Vis spectroscopic techniques. The adsorption of DPPH free radical on the clean and hydrated γ-alumina (1 1 0) surface was examined by dispersion corrected density functional theory (DFT-D) and natural bond orbital (NBO) calculations. Also, time-dependent density functional theory (TD-DFT) was used to predict the absorption spectra. The adsorption was occurred through the interaction of radical nitrogen N and NO 2 groups of DPPH with the acidic and basic sites of γ-alumina surface. The high potential for the adsorption of DPPH radical on γ-alumina nanoparticles was investigated. Interaction of DPPH with Brønsted and Lewis acidic sites of γ-alumina was more favored than Brønsted basic sites. The following order for the adsorption of DPPH over the different active sites of γ-alumina was predicted: Brønsted base < Lewis acid < Brønsted acid. These results are of great significance for the environmental application of γ-alumina nanoparticles in order to remove free radicals. Copyright © 2018. Published by Elsevier B.V.

Spectroscopic and DFT-based computational studies on the molecular electronic structural characteristics and the third-order nonlinear property of an organic NLO crystal: (E)-N‧-(4-chlorobenzylidene)-4-methylbenzenesulfonohydrazide

NASA Astrophysics Data System (ADS)

Sasikala, V.; Sajan, D.; Joseph, Lynnette; Balaji, J.; Prabu, S.; Srinivasan, P.

2017-04-01

Single crystals of (E)-N‧-(4-chlorobenzylidene)-4-methylbenzenesulfonohydrazide (CBMBSH) have been grown by slow evaporation crystal growth method. The structure stabilizing intramolecular donor-acceptor interactions and the presence of the Nsbnd H⋯O, Csbnd H⋯O and Csbnd H⋯C(π) hydrogen bonds in the crystal were confirmed by vibrational spectroscopic and DFT methods. The linear optical absorption characteristics of the solvent phase of CBMBSH were investigated using UV-Vis-NIR spectroscopic and TD-DFT approaches. The 2PA assisted RSA nonlinear absorption and the optical limiting properties of CBMBSH were studied using the open-aperture Z-scan method. The topological characteristics of the electron density have been determined using the quantum theory of atoms in molecules method.

Synthesis and corrosion inhibition application of NATN on mild steel surface in acidic media complemented with DFT studies

NASA Astrophysics Data System (ADS)

Al-Baghdadi, Shaimaa B.; Hashim, Fanar G.; Salam, Ahmed Q.; Abed, Talib K.; Gaaz, Tayser Sumer; Al-Amiery, Ahmed A.; Kadhum, Abdul Amir H.; Reda, Khalid S.; Ahmed, Wahab K.

2018-03-01

The corrosion inhibition effectiveness of thiosemicarbazide compound, namely 3-nitro-5-(2-amino-1,3,4-thiadiazolyl)nitrobenzene (NATN), on mild steel in 1 M hydrochloric acid media has been investigated by weight loss technique. The results exhibit that the corrosion ratio of mild steel was reduced regarding to adding NATN. The corrosion inhibition rate for the NATN was 92.3% at the highest investigated NATN concentration. From the weight loss results it could be concluded that NATN with sulfur, nitrogen and oxygen atoms has clarified best corrosion inhibition achievement comparing to 3,5-dinitrobenzoic acid. Regarding to theoretical studies, DFT was employee to figured geometrical structure and electronic characteristics on NATN. The investigation have been extensive to the HOMO and LUMO analysis to evaluate the energy gap, Ionization potential, Electron Affinity, Global Hardness, Chemical Potential, Electrophilicity, Electronegativity and Polarizability.

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.

FTIR and FT-Raman spectra and DFT vibrational analysis of phosphorus-containing dendrons

NASA Astrophysics Data System (ADS)

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

2008-12-01

FTIR and FT-Raman spectra of four generations of phosphorus-containing dendrons with terminal aldehyde or P sbnd Cl groups have been recorded and analyzed. Their spectral patterns are determined by the ratio T/ R ( T, the number of terminal groups; R, the number of repeated units). Bands assigned to the core, repeated units and terminal groups were separated by the difference spectroscopy method. The optimized geometry, frequencies and intensity of IR bands of G1v generation dendron with terminal aldehyde groups were obtained by the density functional theory (DFT). It was found that the internal skeleton of molecules exists in a single stable conformation with planar sbnd O- C6H4- CHdbnd N- N( CH3)- P( dbnd S)< fragments, but terminal groups may adopt the t, g, g- and t,- g, g-rotational isomers. The t,- g, g-conformer is 0.74 kcal/mol less stable compared to the t, g, g-conformer. The bond length and bond angles obtained by DFT show the best agreement with experimental data. Relying on DFT calculations a complete assignment of vibrations is proposed for different parts of the studied dendrons. The calculated frequencies and intensity of IR bands of the t, g, g- and t,- g, g-conformers of G1v are found to be in reasonable agreement with the experimental results. The most reactive site in dendron is the core function and vinyl group is preferred for nucleophilic attack. In dendrimer the most reactive are the terminal groups.

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.

Accurate electronic and chemical properties of 3d transition metal oxides using a calculated linear response U and a DFT + U(V) method.

PubMed

Xu, Zhongnan; Joshi, Yogesh V; Raman, Sumathy; Kitchin, John R

2015-04-14

We validate the usage of the calculated, linear response Hubbard U for evaluating accurate electronic and chemical properties of bulk 3d transition metal oxides. We find calculated values of U lead to improved band gaps. For the evaluation of accurate reaction energies, we first identify and eliminate contributions to the reaction energies of bulk systems due only to changes in U and construct a thermodynamic cycle that references the total energies of unique U systems to a common point using a DFT + U(V) method, which we recast from a recently introduced DFT + U(R) method for molecular systems. We then introduce a semi-empirical method based on weighted DFT/DFT + U cohesive energies to calculate bulk oxidation energies of transition metal oxides using density functional theory and linear response calculated U values. We validate this method by calculating 14 reactions energies involving V, Cr, Mn, Fe, and Co oxides. We find up to an 85% reduction of the mean average error (MAE) compared to energies calculated with the Perdew-Burke-Ernzerhof functional. When our method is compared with DFT + U with empirically derived U values and the HSE06 hybrid functional, we find up to 65% and 39% reductions in the MAE, respectively.

First-Principles DFT Studies of the Vibrational Properties of Germanene Nanoflakes

NASA Astrophysics Data System (ADS)

Richardson, Steven; Peroparde, Borja; Andrade, Xavier; Aspuru-Guzik, AláN.

The germanium analogue of graphene, germanene, is a potentially new atomically thin quantum material which theory predicts will possess unique transport and optoelectronic properties. Recently, there have been a number of experimental efforts to successfully grow two-dimensional films of germanene on noble metal substrates using molecular beam epitaxy. In addition to this top-down approach of synthesizing large scale films of germanene, we would like to focus on a bottom-up approach where nanoflakes of germanene could be used as molecular seeds or precursors to grow large films of two-dimensional germanene. A knowledge of their infrared and Raman spectra will be critical for characterizing these germanene nanoflakes in future experiments. In this work we used density-functional theory (DFT) to compute the vibrational spectra of a selected number of lower order germanene nanoflakes (e.g. hexagermabenzene, germa-naphthalene, germa-anthracene, germa-phenanthrene, germa-pyrene, germa-tetracene, and germa-pentacene). Our DFT studies also reveal that these germanene nanoflakes are vibrationally stable with buckling of these molecules from their normal two-dimensional planar forms which exist in graphene nanoflakes. This research is supported by NSF Grant No. DMR-1231319.

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.

Functionalization of ( n, 0) CNTs ( n = 3-16) by uracil: DFT studies

NASA Astrophysics Data System (ADS)

Mirzaei, Mahmoud; Harismah, Kun; Jafari, Elham; Gülseren, Oğuz; Rad, Ali Shokuhi

2018-01-01

Density functional theory (DFT) calculations were performed to investigate stabilities and properties for uracil (U)-functionalized carbon nanotubes (CNTs). To this aim, the optimized molecular properties were evaluated for ( n, 0) models of CNTs ( n = 3-16) in the original and U-functionalized forms. The results indicated that the dipole moments and energy gaps were independent of tubular diameters whereas the binding energies showed that the U-functionalization could be better achieved for n = 8-11 curvatures of ( n, 0) CNTs. Further studies based on the evaluated atomic-scale properties, including quadrupole coupling constants ( C Q ), indicated that the electronic properties of atoms could detect the effects of diameters variations of ( n, 0) CNTs, in which the effects were very much significant for the atoms around the U-functionalization regions. Finally, the achieved results of singular U, original CNTs, and CNT-U hybrids were compared to each other to demonstrate the stabilities and properties for the U-functionalized ( n, 0) CNTs.

A conceptual DFT study of the molecular properties of glycating carbonyl compounds.

PubMed

Frau, Juan; Glossman-Mitnik, Daniel

2017-01-01

Several glycating carbonyl compounds have been studied by resorting to the latest Minnesota family of density functional with the objective of determinating their molecular properties. In particular, the chemical reactivity descriptors that arise from conceptual density functional theory and chemical reactivity theory have been calculated through a [Formula: see text]SCF protocol. The validity of the KID (Koopmans' in DFT) procedure has been checked by comparing the reactivity descriptors obtained from the values of the HOMO and LUMO with those calculated through vertical energy values. The reactivity sites have been determined by means of the calculation of the Fukui function indices, the condensed dual descriptor [Formula: see text] and the electrophilic and nucleophilic Parr functions. The glycating power of the studied compounds have been compared with the same property for simple carbohydrates.Graphical abstractSeveral glycating carbonyl compounds have been studied by resorting to the latest Minnesota family of density functional with the objective of determinating their molecular properties, the chemical reactivity descriptors and the validity of the KID (Koopmans' in DFT) procedure.

Orientation of N-benzoyl glycine on silver nanoparticles: SERS and DFT studies

NASA Astrophysics Data System (ADS)

Parameswari, A.; Asath, R. Mohamed; Premkumar, R.; Benial, A. Milton Franklin

2017-05-01

Surface enhanced Raman scattering (SERS) studies of N-benzoyl glycine (NBG) adsorbed on silver nanoparticles (AgNPs) was studied by experimental and density functional theory (DFT) approach. Single crystals of NBG were prepared using slow evaporation method. The AgNPs were prepared and characterized. The DFT/ B3PW91 method with LanL2DZ basis set was used to optimize the molecular structure of NBG and NBG adsorbed on silver cluster. The calculated and observed vibrational frequencies were assingned on the basis of potential energy distribution calculation. The reduced band gap value was obtained for NBG adsorbed on silver nanoparticles from the frontier molecular orbitals analysis. Natural bond orbital analysis was carried out to inspect the intra-molecular stabilization interactions, which are responsible for the bio activity and nonlinear optical property of the molecule. The spectral analysis was also evidenced that NBG would adsorb tilted orientation on the silver surface over the binding sites such as lone pair electron of N atom in amine group and through phenyl ring π system.

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.

NO Chemisorption on Cu/SSZ-13: a Comparative Study from Infrared Spectroscopy and DFT Calculations

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

Zhang, Renqin; McEwen, Jean-Sabin; Kollar, Marton

The locations and energies of Cu ions in a Cu/SSZ-13 zeolite catalyst were investigated by density functional theory (DFT) calculations. For 'naked' Cu2+ ions (i.e., Cu2+ ions with no ligands in their coordination spheres other than zeolite lattice oxygen atoms), the more energetically favorable sites are within a 6-membered ring. However, with the presence of various adsorbates, the energy difference between 6- and 8-membered ring locations greatly diminishes. Specifically, Cu2+ ions are substantially stabilized by -OH ligands (as [CuII(OH)]+), making the extra-framework sites in an 8-membered ring energetically more favorable than 6-membered ring sites. Under fully dehydrated high vacuum conditionsmore » with different Si/Al and Cu/Al ratios, three chemisorbed NO species coexist upon exposure of NO to Cu/SSZ-13: NO+, Cu2+-NO and Cu+-NO. The relative signal intensities for these bands vary greatly with Si/Al ratios. The vibrational frequency of chemisorbed NO was found to be very sensitive to the location of Cu2+ ions. On the one hand, with the aid from DFT calculations, the nature for these vibrations can be assigned in detail. On the other hand, the relative intensities for various Cu2+-NO species provide a good measure of the nature of Cu2+ ions as functions of Si/Al and Cu/Al ratios and the presence of humidity. These new findings cast doubt on the generally accepted proposal that only Cu2+ ions located in 6-membered rings are catalytically active for NH3-SCR.« less

Quantitative DFT modeling of product concentration in organometallic reactions: Cu-mediated pentafluoroethylation of benzoic acid chlorides as a case study.

PubMed

Jover, Jesús

2017-11-08

DFT calculations are widely used for computing properties, reaction mechanisms and energy profiles in organometallic reactions. A qualitative agreement between the experimental and the calculated results seems to usually be enough to validate a computational methodology but recent advances in computation indicate that a nearly quantitative agreement should be possible if an appropriate DFT study is carried out. Final percent product concentrations, often reported as yields, are by far the most commonly reported properties in experimental metal-mediated synthesis studies but reported DFT studies have not focused on predicting absolute product amounts. The recently reported stoichiometric pentafluoroethylation of benzoic acid chlorides (R-C 6 H 4 COCl) with [(phen)Cu(PPh 3 )C 2 F 5 ] (phen = 1,10-phenanthroline, PPh 3 = triphenylphosphine) has been used as a case study to check whether the experimental product concentrations can be reproduced by any of the most popular DFT approaches with high enough accuracy. To this end, the Gibbs energy profile for the pentafluoroethylation of benzoic acid chloride has been computed using 14 different DFT methods. These computed Gibbs energy profiles have been employed to build kinetic models predicting the final product concentration in solution. The best results are obtained with the D3-dispersion corrected B3LYP functional, which has been successfully used afterwards to model the reaction outcomes of other simple (R = o-Me, p-Me, p-Cl, p-F, etc.) benzoic acid chlorides. The product concentrations of more complex reaction networks in which more than one position of the substrate may be activated by the copper catalyst (R = o-Br and p-I) are also predicted appropriately.

Density Functional Theory (DFT) Study of Molecularly Imprinted Polymer (MIP) Methacrylic Acid (MAA) with D-Glucose

NASA Astrophysics Data System (ADS)

Wungu, T. D. K.; Marsha, S. E.; Widayani; Suprijadi

2017-07-01

In order to find an alternative biosensor material which enables to detect the glucose level, therefore in this study, the interaction between Methacrylic Acid (MAA) based Molecularly Imprinted Polymer (MIP) with D-Glucose is investigated using the Density Functional Theory (DFT). The aim of this study is to determine whether a molecule of the MAA can be functioned as a bio-sensing of glucose. In this calculation, the Gaussian 09 with B3LYP and 631+G(d) basis sets is used to calculate all electronic properties. It is found that the interaction between a molecule of MAA and a molecule of D-Glucose was observed through the shortened distance between the two molecules. The binding energy of MAA/D-glucose and the Mulliken population analysis are investigated for checking possible interaction. From analysis, the MAA based MIP can be used as a bio-sensing material.

Using DFT methodology for more reliable predictive models: Design of inhibitors of Golgi α-Mannosidase II.

PubMed

Bobovská, Adela; Tvaroška, Igor; Kóňa, Juraj

2016-05-01

Human Golgi α-mannosidase II (GMII), a zinc ion co-factor dependent glycoside hydrolase (E.C.3.2.1.114), is a pharmaceutical target for the design of inhibitors with anti-cancer activity. The discovery of an effective inhibitor is complicated by the fact that all known potent inhibitors of GMII are involved in unwanted co-inhibition with lysosomal α-mannosidase (LMan, E.C.3.2.1.24), a relative to GMII. Routine empirical QSAR models for both GMII and LMan did not work with a required accuracy. Therefore, we have developed a fast computational protocol to build predictive models combining interaction energy descriptors from an empirical docking scoring function (Glide-Schrödinger), Linear Interaction Energy (LIE) method, and quantum mechanical density functional theory (QM-DFT) calculations. The QSAR models were built and validated with a library of structurally diverse GMII and LMan inhibitors and non-active compounds. A critical role of QM-DFT descriptors for the more accurate prediction abilities of the models is demonstrated. The predictive ability of the models was significantly improved when going from the empirical docking scoring function to mixed empirical-QM-DFT QSAR models (Q(2)=0.78-0.86 when cross-validation procedures were carried out; and R(2)=0.81-0.83 for a testing set). The average error for the predicted ΔGbind decreased to 0.8-1.1kcalmol(-1). Also, 76-80% of non-active compounds were successfully filtered out from GMII and LMan inhibitors. The QSAR models with the fragmented QM-DFT descriptors may find a useful application in structure-based drug design where pure empirical and force field methods reached their limits and where quantum mechanics effects are critical for ligand-receptor interactions. The optimized models will apply in lead optimization processes for GMII drug developments. Copyright © 2016 Elsevier Inc. All rights reserved.

Vibrational spectroscopic studies, NLO, HOMO-LUMO and electronic structure calculations of α,α,α-trichlorotoluene using HF and DFT.

PubMed

Govindarajan, M; Karabacak, M; Periandy, S; Xavier, S

2012-08-01

FT-IR and FT-Raman spectra of α,α,α-trichlorotoluene have been recorded and analyzed. The geometry, fundamental vibrational frequencies are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) B3LYP/6-311++G(d,p) method and a comparative study between HF level and various basis sets combination. The fundamental vibrational wavenumbers as well as their intensities were calculated and a good agreement between observed and scaled calculated wavenumbers has been achieved. The complete vibrational assignments of wavenumbers are made on the basis of potential energy distribution (PED). The effects due to the substitutions of methyl group and halogen were investigated. The absorption energy and oscillator strength are calculated by time-dependent density functional theory (TD-DFT). The electric dipole moment, polarizability and the first hyperpolarizability values of the α,α,α-trichlorotoluene have been calculated. (1)H NMR chemical shifts were calculated by using the gauge independent atomic orbital (GIAO) method with HF and B3LYP methods with 6-311++G(d,p) basis set. Moreover, molecular electrostatic potential (MEP) and thermodynamic properties were performed. Mulliken and natural charges of the title molecule were also calculated and interpreted. Copyright © 2012 Elsevier B.V. All rights reserved.

Zinc binding in HDAC inhibitors: a DFT study.

PubMed

Wang, Difei; Helquist, Paul; Wiest, Olaf

2007-07-06

Histone deacetylases (HDACs) are attractive targets for the treatment of cancers and a variety of other diseases. Most currently studied HDAC inhibitors contain hydroxamic acids, which are potentially problematic in the development of practical drugs. DFT calculations of the binding modes and free energies of binding for a variety of other functionalities in a model active site of HDAC are described. The protonation state of hydroxamic acids in the active site and the origin of the high affinity are discussed. These results emphasize the importance of a carefully chosen pKa for zinc binding and provide guidance for the design of novel, non-hydroxamic acid HDAC inhibitors.

Structure prediction of nanoclusters; a direct or a pre-screened search on the DFT energy landscape?

PubMed

Farrow, M R; Chow, Y; Woodley, S M

2014-10-21

The atomic structure of inorganic nanoclusters obtained via a search for low lying minima on energy landscapes, or hypersurfaces, is reported for inorganic binary compounds: zinc oxide (ZnO)n, magnesium oxide (MgO)n, cadmium selenide (CdSe)n, and potassium fluoride (KF)n, where n = 1-12 formula units. The computational cost of each search is dominated by the effort to evaluate each sample point on the energy landscape and the number of required sample points. The effect of changing the balance between these two factors on the success of the search is investigated. The choice of sample points will also affect the number of required data points and therefore the efficiency of the search. Monte Carlo based global optimisation routines (evolutionary and stochastic quenching algorithms) within a new software package, viz. Knowledge Led Master Code (KLMC), are employed to search both directly and after pre-screening on the DFT energy landscape. Pre-screening includes structural relaxation to minimise a cheaper energy function - based on interatomic potentials - and is found to improve significantly the search efficiency, and typically reduces the number of DFT calculations required to locate the local minima by more than an order of magnitude. Although the choice of functional form is important, the approach is robust to small changes to the interatomic potential parameters. The computational cost of initial DFT calculations of each structure is reduced by employing Gaussian smearing to the electronic energy levels. Larger (KF)n nanoclusters are predicted to form cuboid cuts from the rock-salt phase, but also share many structural motifs with (MgO)n for smaller clusters. The transition from 2D rings to 3D (bubble, or fullerene-like) structures occur at a larger cluster size for (ZnO)n and (CdSe)n. Differences between the HOMO and LUMO energies, for all the compounds apart from KF, are in the visible region of the optical spectrum (2-3 eV); KF lies deep in the UV region

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.

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.

A Novel DFT-Based DOA Estimation by a Virtual Array Extension Using Simple Multiplications for FMCW Radar

PubMed Central

Kim, Bongseok; Kim, Sangdong; Lee, Jonghun

2018-01-01

We propose a novel discrete Fourier transform (DFT)-based direction of arrival (DOA) estimation by a virtual array extension using simple multiplications for frequency modulated continuous wave (FMCW) radar. DFT-based DOA estimation is usually employed in radar systems because it provides the advantage of low complexity for real-time signal processing. In order to enhance the resolution of DOA estimation or to decrease the missing detection probability, it is essential to have a considerable number of channel signals. However, due to constraints of space and cost, it is not easy to increase the number of channel signals. In order to address this issue, we increase the number of effective channel signals by generating virtual channel signals using simple multiplications of the given channel signals. The increase in channel signals allows the proposed scheme to detect DOA more accurately than the conventional scheme while using the same number of channel signals. Simulation results show that the proposed scheme achieves improved DOA estimation compared to the conventional DFT-based method. Furthermore, the effectiveness of the proposed scheme in a practical environment is verified through the experiment. PMID:29758016

DFT-based prediction of reactivity of short-chain alcohol dehydrogenase

NASA Astrophysics Data System (ADS)

Stawoska, I.; Dudzik, A.; Wasylewski, M.; Jemioła-Rzemińska, M.; Skoczowski, A.; Strzałka, K.; Szaleniec, M.

2017-06-01

The reaction mechanism of ketone reduction by short chain dehydrogenase/reductase, ( S)-1-phenylethanol dehydrogenase from Aromatoleum aromaticum, was studied with DFT methods using cluster model approach. The characteristics of the hydride transfer process were investigated based on reaction of acetophenone and its eight structural analogues. The results confirmed previously suggested concomitant transfer of hydride from NADH to carbonyl C atom of the substrate with proton transfer from Tyr to carbonyl O atom. However, additional coupled motion of the next proton in the proton-relay system, between O2' ribose hydroxyl and Tyr154 was observed. The protonation of Lys158 seems not to affect the pKa of Tyr154, as the stable tyrosyl anion was observed only for a neutral Lys158 in the high pH model. The calculated reaction energies and reaction barriers were calibrated by calorimetric and kinetic methods. This allowed an excellent prediction of the reaction enthalpies (R2 = 0.93) and a good prediction of the reaction kinetics (R2 = 0.89). The observed relations were validated in prediction of log K eq obtained for real whole-cell reactor systems that modelled industrial synthesis of S-alcohols.

Expedient and click synthesis, spectroscopic characterizations and DFT calculations of novel 1,5-bis(N-substituted 1,2,3‒triazole) benzodiazepinedione scaffolds

NASA Astrophysics Data System (ADS)

Paghandeh, Hossein; Saeidian, Hamid

2018-04-01

A practically reliable procedure for synthesis of new 1,5-bis(N-substituted 1,2,3‒triazole) benzodiazepinedione derivatives was reported by sequential amidation, propargylation and a click azide‒alkyne [3 + 2] cycloaddition reaction in a one pot fashion. The desired products were characterized by CHN analysis, 1H and 13C NMR and ESI-MS spectroscopy. Short reaction time, good yields (55-91%), mild reaction conditions and easily available and less expensive starting materials are advantages of this protocol. Natural bond orbital charge distribution and HOMO-LUMO analysis of the characterized structure of 4e have been also calculated by density functional theory (DFT) calculations. The Li+ and Na+ ion affinities of 4e have been also investigated by DFT studies to find the applicability of these products as ligand in coordination chemistry. Sodium ion affinity of 4e was determined as 60 kJ mol-1 is less than its lithium ion affinity, indicating that the lithiation of 4e is more exothermic than the sodiation.

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.

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.

Comparison of DFT-S-orthogonal frequency division multiplexing and single-carrier in a radio-over-fiber system

NASA Astrophysics Data System (ADS)

Wang, Kaihui; Li, Xinying; Yu, Jianjun

2017-09-01

DFT-S-orthogonal frequency division multiplexing (OFDM) and single-carrier (SC) modulation are two typical modulation formats in radio-over-fiber (RoF) systems. They may have respective advantages and disadvantages in different scenarios. Therefore, bit error ratio comparison results of these two modulation formats will be useful for designing and optimizing the practical RoF system. We experimentally compare these two modulation formats in a long wireless distance RoF system at W-band. It can be concluded that DFT-S-OFDM and SC modulation have similar performances in a RoF system with transmission distance over 80-km fiber and 224-m wireless link.

The influence of the dispersion corrections on the performance of DFT method in modeling HNgY noble gas molecules and their complexes

NASA Astrophysics Data System (ADS)

Cukras, Janusz; Sadlej, Joanna

2018-01-01

The letter reports a comparative assessment of the usefulness of the two different Grimme's corrections for evaluating dispersion interaction (DFT-D3 and DFT-D3BJ) for the representative molecules of the family of noble-gas hydrides HXeY and their complexes with the HZ molecules, where Y and Z are F/Cl/OH/SH. with special regard to the dispersion term calculated by means of the symmetry-adapted perturbation theory (at the SAPT0 level). The results indicate that despite differences in the total interactions energy (DFT + corrections) versus SAPT0 results, the sequence of contributions of the individual dispersion terms is still maintained. Both dispersion corrections perform similarly and they improve the results suggesting that it is worthwhile to include them in calculations.

Extreme Basicity of Biguanide Drugs in Aqueous Solutions: Ion Transfer Voltammetry and DFT Calculations.

PubMed

Langmaier, Jan; Pižl, Martin; Samec, Zdeněk; Záliš, Stanislav

2016-09-22

Ion transfer voltammetry is used to estimate the acid dissociation constants Ka1 and Ka2 of the mono- and diprotonated forms of the biguanide drugs metformin (MF), phenformin (PF), and 1-phenylbiguanide (PB) in an aqueous solution. Measurements gave the pKa1 values for MFH(+), PFH(+), and PBH(+) characterizing the basicity of MF, PF, and PB, which are significantly higher than those reported in the literature. As a result, the monoprotonated forms of these biguanides should prevail in a considerably broader range of pH 1-15 (MFH(+), PFH(+)) and 2-13 (PBH(+)). DFT calculations with solvent correction were performed for possible tautomeric forms of neutral, monoprotonated, and diprotonated species. Extreme basicity of all drugs is confirmed by DFT calculations of pKa1 for the most stable tautomers of the neutral and protonated forms with explicit water molecules in the first solvation sphere included.

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.

Electronic properties of hexagonal gallium phosphide: A DFT investigation

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

Kumar, Vipin; Shah, Esha V.; Roy, Debesh R., E-mail: drr@ashd.svnit.ac.in

2016-05-23

A detail density functional investigation is performed to develop hexagonal 2D gallium phosphide material. The geometry, band structure and density of states (total and projected) of 2D hexagonal GaP are reported in detail. It is heartening to note that the developed material is identified as an indirect band gap semiconductor. The indirect gap for this material is predicted as 1.97 eV at K-Γ, and a direct gap of 2.28 eV at K point is achieved, which is very close to the reported direct band gap for zinc blende and buckled structures of GaP.

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

A DFT study on surface-enhanced Raman spectroscopy of aromatic dithiol derivatives adsorbed on gold nanojunctions

NASA Astrophysics Data System (ADS)

You, Tingting; Lang, Xiufeng; Huang, Anping; Yin, Penggang

2018-01-01

A computational study on aromatic dithiol derivatives (HS-Ar-X-Ar-SH, X = O, S, Se, NH, CH2, Ndbnd N, CHdbnd CH, Ctbnd C) interacting with gold cluster(s) was presented to investigate the chemical enhancement mechanism related to surface-enhanced Raman spectroscopy (SERS) for molecular junctions. Density functional theory (DFT) were performed on derivatives molecules as well as their single-end-linked (SEL) or double-end-linked (DEL) complexes for geometric, spectra, electronic and excitation properties, leading to discussions on dominant factor during SERS process. The resulted enhancement factors of SEL and DEL complexes exhibited specific dependency on linking atom or functional group between two phenyls, which was in accordance with the variation of polarizabilities and molecule-cluster transition energy.

Wannier-function-based constrained DFT with nonorthogonality-correcting Pulay forces in application to the reorganization effects in graphene-adsorbed pentacene

NASA Astrophysics Data System (ADS)

Roychoudhury, Subhayan; O'Regan, David D.; Sanvito, Stefano

2018-05-01

Pulay terms arise in the Hellmann-Feynman forces in electronic-structure calculations when one employs a basis set made of localized orbitals that move with their host atoms. If the total energy of the system depends on a subspace population defined in terms of the localized orbitals across multiple atoms, then unconventional Pulay terms will emerge due to the variation of the orbital nonorthogonality with ionic translation. Here, we derive the required exact expressions for such terms, which cannot be eliminated by orbital orthonormalization. We have implemented these corrected ionic forces within the linear-scaling density functional theory (DFT) package onetep, and we have used constrained DFT to calculate the reorganization energy of a pentacene molecule adsorbed on a graphene flake. The calculations are performed by including ensemble DFT, corrections for periodic boundary conditions, and empirical Van der Waals interactions. For this system we find that tensorially invariant population analysis yields an adsorbate subspace population that is very close to integer-valued when based upon nonorthogonal Wannier functions, and also but less precisely so when using pseudoatomic functions. Thus, orbitals can provide a very effective population analysis for constrained DFT. Our calculations show that the reorganization energy of the adsorbed pentacene is typically lower than that of pentacene in the gas phase. We attribute this effect to steric hindrance.

A chaotic modified-DFT encryption scheme for physical layer security and PAPR reduction in OFDM-PON

NASA Astrophysics Data System (ADS)

Fu, Xiaosong; Bi, Meihua; Zhou, Xuefang; Yang, Guowei; Li, Qiliang; Zhou, Zhao; Yang, Xuelin

2018-05-01

This letter proposes a modified discrete Fourier transform (DFT) encryption scheme with multi-dimensional chaos for the physical layer security and peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing passive optical network (OFDM-PON) system. This multiple-fold encryption algorithm is mainly composed by using the column vectors permutation and the random phase encryption in the standard DFT matrix, which can create ∼10551 key space. The transmission of ∼10 Gb/s encrypted OFDM signal is verified over 20-km standard single mode fiber (SMF). Moreover, experimental results show that, the proposed scheme can achieve ∼2.6-dB PAPR reduction and ∼1-dB improvement of receiver sensitivity if compared with the common OFDM-PON.

Investigating the Energetic Ordering of Stable and Metastable TiO 2 Polymorphs Using DFT+ U and Hybrid Functionals

DOE PAGES

Curnan, Matthew T.; Kitchin, John R.

2015-08-12

Prediction of transition metal oxide BO 2 (B = Ti, V, etc.) polymorph energetic properties is critical to tunable material design and identifying thermodynamically accessible structures. Determining procedures capable of synthesizing particular polymorphs minimally requires prior knowledge of their relative energetic favorability. Information concerning TiO 2 polymorph relative energetic favorability has been ascertained from experimental research. In this study, the consistency of first-principles predictions and experimental results involving the relative energetic ordering of stable (rutile), metastable (anatase and brookite), and unstable (columbite) TiO 2 polymorphs is assessed via density functional theory (DFT). Considering the issues involving electron–electron interaction and chargemore » delocalization in TiO 2 calculations, relative energetic ordering predictions are evaluated over trends varying Ti Hubbard U 3d or exact exchange fraction parameter values. Energetic trends formed from varying U 3d predict experimentally consistent energetic ordering over U 3d intervals when using GGA-based functionals, regardless of pseudopotential selection. Given pertinent linear response calculated Hubbard U values, these results enable TiO 2 polymorph energetic ordering prediction. Here, the hybrid functional calculations involving rutile–anatase relative energetics, though demonstrating experimentally consistent energetic ordering over exact exchange fraction ranges, are not accompanied by predicted fractions, for a first-principles methodology capable of calculating exact exchange fractions precisely predicting TiO 2 polymorph energetic ordering is not available.« less

Multiscale Investigations of the Early Stage Oxidation on Cu Surfaces

NASA Astrophysics Data System (ADS)

Zhu, Qing; Xiao, Penghao; Lian, Xin; Yang, Shen-Che; Henkelman, Grame; Saidi, Wissam; Yang, Judith; University of Pittsburgh Team; University of Texas at Austin Team

Previous in situ TEM experiments have shown that the oxidation of the three low index Cu surfaces (100), (110) and (111) exhibit different oxide nucleation rates, and the resulting oxides have 3-dimensional (3D) island shapes or 2D rafts under different conditions. In order to better understand these results, we have investigated the early stages of Cu oxidation using a multiscale computational approach that employs density functional theory (DFT), reactive force field (ReaxFF), and kinetic Mote Carlo (KMC). With DFT calculation, we have compared O2 dissociation barriers on Cu (100), (110) and (111) surfaces at high oxygen coverage to evaluate the kinetic barrier of sublayer oxidization. We found that O2 dissociation barriers on Cu(111) surface are all lower than those on (110) and (100) surfaces. This trend agrees with experimental observations that (111) surface is easier to oxidize. These DFT calculated energy barriers are then incorporated into KMC simulations. The large scale ReaxFF molecular dynamics and KMC simulations detail the oxidation dynamics of the different Cu surfaces, and show the formation of various oxide morphologies that are consistent with experimental observations.

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.

Computing sextic centrifugal distortion constants by DFT: A benchmark analysis on halogenated compounds

NASA Astrophysics Data System (ADS)

Pietropolli Charmet, Andrea; Stoppa, Paolo; Tasinato, Nicola; Giorgianni, Santi

2017-05-01

This work presents a benchmark study on the calculation of the sextic centrifugal distortion constants employing cubic force fields computed by means of density functional theory (DFT). For a set of semi-rigid halogenated organic compounds several functionals (B2PLYP, B3LYP, B3PW91, M06, M06-2X, O3LYP, X3LYP, ωB97XD, CAM-B3LYP, LC-ωPBE, PBE0, B97-1 and B97-D) were used for computing the sextic centrifugal distortion constants. The effects related to the size of basis sets and the performances of hybrid approaches, where the harmonic data obtained at higher level of electronic correlation are coupled with cubic force constants yielded by DFT functionals, are presented and discussed. The predicted values were compared to both the available data published in the literature and those obtained by calculations carried out at increasing level of electronic correlation: Hartree-Fock Self Consistent Field (HF-SCF), second order Møller-Plesset perturbation theory (MP2), and coupled-cluster single and double (CCSD) level of theory. Different hybrid approaches, having the cubic force field computed at DFT level of theory coupled to harmonic data computed at increasing level of electronic correlation (up to CCSD level of theory augmented by a perturbational estimate of the effects of connected triple excitations, CCSD(T)) were considered. The obtained results demonstrate that they can represent reliable and computationally affordable methods to predict sextic centrifugal terms with an accuracy almost comparable to that yielded by the more expensive anharmonic force fields fully computed at MP2 and CCSD levels of theory. In view of their reduced computational cost, these hybrid approaches pave the route to the study of more complex systems.

Rapidly calculated density functional theory (DFT) relaxed Iso-potential Phi Si Maps: Beta-cellobiose

USDA-ARS?s Scientific Manuscript database

New cellobiose Phi-H/Si-H maps are rapidly generated using a mixed basis set DFT method, found to achieve a high level of confidence while reducing computer resources dramatically. Relaxed iso-potential maps are made for different conformational states of cellobiose, showing how glycosidic bond dihe...

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.

Halogen Bonding versus Hydrogen Bonding: A Molecular Orbital Perspective

PubMed Central

Wolters, Lando P; Bickelhaupt, F Matthias

2012-01-01

We have carried out extensive computational analyses of the structure and bonding mechanism in trihalides DX⋅⋅⋅A− and the analogous hydrogen-bonded complexes DH⋅⋅⋅A− (D, X, A=F, Cl, Br, I) using relativistic density functional theory (DFT) at zeroth-order regular approximation ZORA-BP86/TZ2P. One purpose was to obtain a set of consistent data from which reliable trends in structure and stability can be inferred over a large range of systems. The main objective was to achieve a detailed understanding of the nature of halogen bonds, how they resemble, and also how they differ from, the better understood hydrogen bonds. Thus, we present an accurate physical model of the halogen bond based on quantitative Kohn–Sham molecular orbital (MO) theory, energy decomposition analyses (EDA) and Voronoi deformation density (VDD) analyses of the charge distribution. It appears that the halogen bond in DX⋅⋅⋅A− arises not only from classical electrostatic attraction but also receives substantial stabilization from HOMO–LUMO interactions between the lone pair of A− and the σ* orbital of D–X. PMID:24551497

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.

FTIR, Raman, and UV-Vis spectroscopic and DFT investigations of the structure of iron-lead-tellurate glasses.

PubMed

Rada, Simona; Dehelean, Adriana; Culea, Eugen

2011-08-01

In this work, the effects of iron ion intercalations on lead-tellurate glasses were investigated via FTIR, Raman and UV-Vis spectroscopies. This homogeneous glass system has compositions xFe(2)O(3)·(100-x)[4TeO(2)·PbO(2)], where x = 0-60 mol%. The presented observations in these mechanisms show that the lead ions have a pronounced affinity towards [TeO(3)] structural units, resulting in the deformation of the Te-O-Te linkages, and leading to the intercalation of [PbO( n )] (n = 3, 4) and [FeO( n )] (n = 4, 6) entities in the [TeO(4)] chain network. The formation of negatively charged [FeO(4)](1-) structural units implies the attraction of Pb(2+) ions in order to compensate for this electrical charge. Upon increasing the Fe(2)O(3) content to 60 mol%, the network can accommodate an excess of oxygen through the formation of [FeO(6)] structural units and the conversion of [TeO(4)] into [TeO(3)] structural units. For even higher Fe(2)O(3) contents, Raman spectra indicate a greater degree of depolymerization of the vitreous network than FTIR spectra do. The bands due to the Pb-O bond vibrations are very strongly polarized and the [TeO(4)] structural units convert into [TeO(3)] units via an intermediate coordination stage termed "[TeO(3+1)]" structural units. Our UV-Vis spectroscopic data show two mechanisms: (i) the conversion of the Fe(3+) to Fe(2+) at the same time as the oxidation of Pb(2+) to Pb(+4) ions for samples with low Fe(2)O(3) contents; (ii) when the Fe(2)O(3) content is high (x ≥ 50 mol%), the Fe(2+) ions capture positive holes and are transferred to Fe(3+) ions through a photochemical reaction, while the Pb(2+) ions are formed by the reduction of Pb(4+) ions. DFT calculations show that the addition of Fe(2)O(3) to lead-tellurate glasses seems to break the axial Te-O bonds, and the [TeO(4)] structural units are gradually transformed into [TeO(3+1)]- and [TeO(3)]-type polyhedra. Analyzing these data further indicates a gradual

Optimization of training sequence for DFT-spread DMT signal in optical access network with direct detection utilizing DML.

PubMed

Li, Fan; Li, Xinying; Yu, Jianjun; Chen, Lin

2014-09-22

We experimentally demonstrated the transmission of 79.86-Gb/s discrete-Fourier-transform spread 32 QAM discrete multi-tone (DFT-spread 32 QAM-DMT) signal over 20-km standard single-mode fiber (SSMF) utilizing directly modulated laser (DML). The experimental results show DFT-spread effectively reduces Peak-to-Average Power Ratio (PAPR) of DMT signal, and also well overcomes narrowband interference and high frequencies power attenuation. We compared different types of training sequence (TS) symbols and found that the optimized TS for channel estimation is the symbol with digital BPSK/QPSK modulation format due to its best performance against optical link noise during channel estimation.

Enhanced hydrogen storage on Li-doped defective graphene with B substitution: A DFT study

NASA Astrophysics Data System (ADS)

Zhou, Yanan; Chu, Wei; Jing, Fangli; Zheng, Jian; Sun, Wenjing; Xue, Ying

2017-07-01

The characteristics of hydrogen adsorption on Li-doped defective graphene systems were investigated using density functional theory (DFT) calculations. Four types of defective structures were selected. Li atoms were well dispersed on the defective graphene without clustering, evidenced by the binding energy value between Li and defective graphene than that of Li-Lix. Additionally, as the amount of adsorbed H2 molecules increase, the H2 molecules show tilting configuration toward the Li adatom. This is beneficial for more hydrogen adsorption under the electrostatic interaction. On these four stable structures, there were up to three polarized H2 molecules adsorbed on per Li adatom, with the average hydrogen adsorption energy in the range of approximately 0.2-0.4 eV. These results provide new focus on the nature of Li-doped defective graphene with sometimes B substitution medium, which could be considered as a promising candidate for hydrogen storage.

Experimental approach to the anion problem in DFT calculation of the partial charge transfer during adsorption at electrochemical interfaces

NASA Astrophysics Data System (ADS)

Marichev, V. A.

2005-08-01

In DFT calculation of the charge transfer (Δ N), anions pose a special problem since their electron affinities are unknown. There is no method for calculating reasonable values of the absolute electronegativity ( χA) and chemical hardness ( ηA) for ions from data of species themselves. We propose a new approach to the experimental measurement of χA at the condition: Δ N = 0 at which η values may be neglected and χA = χMe. Electrochemical parameters corresponding to this condition may be obtained by the contact electric resistance method during in situ investigation of anion adsorption in the particular system anion-metal.

DFT-based method for more accurate adsorption energies: An adaptive sum of energies from RPBE and vdW density functionals

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

Hensley, Alyssa J. R.; Ghale, Kushal; Rieg, Carolin

In recent years, the popularity of density functional theory with periodic boundary conditions (DFT) has surged for the design and optimization of functional materials. However, no single DFT exchange–correlation functional currently available gives accurate adsorption energies on transition metals both when bonding to the surface is dominated by strong covalent or ionic bonding and when it has strong contributions from van der Waals interactions (i.e., dispersion forces). Here we present a new, simple method for accurately predicting adsorption energies on transition-metal surfaces based on DFT calculations, using an adaptively weighted sum of energies from RPBE and optB86b-vdW (or optB88-vdW) densitymore » functionals. This method has been benchmarked against a set of 39 reliable experimental energies for adsorption reactions. Our results show that this method has a mean absolute error and root mean squared error relative to experiments of 13.4 and 19.3 kJ/mol, respectively, compared to 20.4 and 26.4 kJ/mol for the BEEF-vdW functional. For systems with large van der Waals contributions, this method decreases these errors to 11.6 and 17.5 kJ/mol. Furthermore, this method provides predictions of adsorption energies both for processes dominated by strong covalent or ionic bonding and for those dominated by dispersion forces that are more accurate than those of any current standard DFT functional alone.« less

DFT-based method for more accurate adsorption energies: An adaptive sum of energies from RPBE and vdW density functionals

DOE PAGES

Hensley, Alyssa J. R.; Ghale, Kushal; Rieg, Carolin; ...

2017-01-26

In recent years, the popularity of density functional theory with periodic boundary conditions (DFT) has surged for the design and optimization of functional materials. However, no single DFT exchange–correlation functional currently available gives accurate adsorption energies on transition metals both when bonding to the surface is dominated by strong covalent or ionic bonding and when it has strong contributions from van der Waals interactions (i.e., dispersion forces). Here we present a new, simple method for accurately predicting adsorption energies on transition-metal surfaces based on DFT calculations, using an adaptively weighted sum of energies from RPBE and optB86b-vdW (or optB88-vdW) densitymore » functionals. This method has been benchmarked against a set of 39 reliable experimental energies for adsorption reactions. Our results show that this method has a mean absolute error and root mean squared error relative to experiments of 13.4 and 19.3 kJ/mol, respectively, compared to 20.4 and 26.4 kJ/mol for the BEEF-vdW functional. For systems with large van der Waals contributions, this method decreases these errors to 11.6 and 17.5 kJ/mol. Furthermore, this method provides predictions of adsorption energies both for processes dominated by strong covalent or ionic bonding and for those dominated by dispersion forces that are more accurate than those of any current standard DFT functional alone.« less

Investigation of the adsorption of ozone molecules on TiO2/WSe2 nanocomposites by DFT computations: Applications to gas sensor devices

NASA Astrophysics Data System (ADS)

Abbasi, Amirali; Sardroodi, Jaber Jahanbin

2018-04-01

The adsorption of O3 molecule on the undoped and N-doped TiO2/WSe2 nanocomposites was studied using first principles density functional theory calculations. O3 interaction with TiO2/WSe2 nanocomposites is considered so as to investigate WSe2 effects on the adsorption process. WSe2 favors the adsorption of O3 on TiO2 particles. In other words, WSe2 is conducive to the interaction of O3 molecule with fivefold coordinated titanium sites of TiO2. The effects of vdW interactions were taken into account in order to obtain equilibrium geometries of O3 molecules at TiO2/WSe2 interfaces. For all adsorption configurations, the binding site was positioned on the fivefold coordinated titanium atoms. The results show that the interactions between O3 and TiO2 in TiO2/WSe2 nanocomposites are stronger than those between O3 and bare TiO2, suggesting that WSe2 helps to strengthen the interaction of ozone molecule with TiO2 particles. The results also indicate that the adsorption of the O3 molecule on the N-doped TiO2/WSe2 nanocomposite is more energetically favorable than the adsorption of O3 on the pristine one, representing that the N-doped nanocomposites are more sensitive than the undoped ones. Our DFT results clearly show that the N-doped TiO2/WSe2 nanocomposite would be a promising O3 gas sensor. The electronic structure of the adsorption system was also investigated, including analysis of the total and projected density of states, and charge density differences of the TiO2/WSe2 with adsorbed O3 molecules. The charge density difference calculations indicate that the charges were accumulated over the adsorbed O3 molecule. Besides, the N-doped nanocomposites have better sensing response than the pristine ones. This work was devoted to provide the theory basis for the design and development of novel and advanced O3 sensors based on modified TiO2/WSe2 nanocomposites.

Electron affinity of perhalogenated benzenes: A theoretical DFT study

NASA Astrophysics Data System (ADS)

Volatron, François; Roche, Cécile

2007-10-01

The potential energy surfaces (PES) of unsubstituted and perhalogenated benzene anions ( CX6-, X = F, Cl, Br, and I) were explored by means of DFT-B3LYP calculations. In the F and Cl cases seven extrema were located and characterized. In the Br and I cases only one minimum and two extrema were found. In each case the minimum was recomputed at the CCSD(T) level. The electron affinities of C 6X 6 were calculated (ZPE included). The results obtained agree well with the experimental determinations when available. The values obtained in the X = Br and the X = I cases are expected to be valuable predictions.

A microscopic study investigating the structure of SnSe surfaces

NASA Astrophysics Data System (ADS)

Kim, Sang-ui; Duong, Anh-Tuan; Cho, Sunglae; Rhim, S. H.; Kim, Jungdae

2016-09-01

SnSe has been widely studied due to its many potential applications that take advantage of its excellent thermoelectric, photovoltaic, and optoelectronic properties. However, experimental investigations into the microscopic structure of SnSe remain largely unexplored. Herein, for the first time, the atomic and electronic structures of SnSe surfaces are studied by a home-built low temperature scanning tunneling microscope (STM) and density functional theory (DFT) calculations. The cleaved surface of SnSe is comprised of covalently bonded Se and Sn atoms in zigzag patterns. However, rectangular periodicity was observed in the atomic images of SnSe surfaces for filled and empty state probing. Detailed atomic structures are analyzed by DFT calculations, indicating that the bright extrusions of both filled and empty state images are mostly located at the positions of Sn atoms.

Dye-sensitized solar cells and complexes between pyridines and iodines. A NMR, IR and DFT study.

PubMed

Hansen, Poul Erik; Nguyen, Phuong Tuyet; Krake, Jacob; Spanget-Larsen, Jens; Lund, Torben

2012-12-01

Interactions between triiodide (I(3)(-)) and 4-tert-butylpyridine (4TBP) as postulated in dye-sensitized solar cells (DSC) are investigated by means of (13)C NMR and IR spectroscopy supported by DFT calculations. The charge transfer (CT) complex 4TBP·I(2) and potential salts such as (4TBP)(2)I(+), I(3)(-) were synthesized and characterized by IR and (13)C NMR spectroscopy. However, mixing (butyl)(4)N(+), I(3)(-) and 4TBP at concentrations comparable to those of the DSC solar cell did not lead to any reaction. Neither CT complexes nor cationic species like (4TBP)(2)I(+) were observed, judging from the (13)C NMR spectroscopic evidence. This questions the previously proposed formation of (4TBP)(2)I(+) in DSC cells. Copyright © 2012 Elsevier B.V. All rights reserved.

On the Interaction between Carbon Dioxide and Nanomaterials with High Accuracy ab initio and DFT Calculations

NASA Astrophysics Data System (ADS)

Vogiatzis, Konstantinos D.; Mavrandonakis, Antreas; Klopper, Wim; Froudakis, George

2009-08-01

The separation, capture and storage of carbon dioxide from the flue gas is an environmental and economical problem of significant importance. Zeolites and activated carbons have been used from the industries in order to reduce the emissions of CO2. A new family of materials, the metal-organic frameworks (MOFs), has been recently proposed as an efficient substitute of the abovementioned materials. In particular, materials based on zinc complexes with imidazo-like aromatic compounds which builds frameworks similar with those of Zeolites (Zeolite-Imidazolium Frameworks, ZIFs), have the potential for efficient separation of CO2 from CO and CH4. [1]. Weak interactions between carbon dioxide and heterocyclic aromatic compounds are being examined with high accuracy ab initio methods. CO2 has zero dipole moment but a significant quadrupole moment enables it to operate as a weak acid or weak base, according to his environment. Nitrogen-containing aromatic compounds act as electron donors, while CO2 acts as an electron acceptor. Electrostatic interactions induce a non-permanent dipole moment on CO2 and the complex is stabilized by in-plane hydrogen bonds between the charged oxygens of CO2 and nearby hydrogen of the aromatic molecule. In addition, dispersion forces from the electron correlation contribute to the interaction energy. By using explicitly correlated methods (MP2-F12/aug-cc-pVTZ) [2] and by adding the contribution from the triples excitations, calculated with a smaller basis (6-311++G**), we reach to an approximate CCSD(T) complete basis set result. [3] Extrapolation schemes were used in order to reach the MP2 basis set limit and compare it with the CCSD(T)/CBS result. Those results are in excellent agreement with the explicitly correlated MP2-F12. In addition, our complexes are being investigated with DFT methods that calculate separately the dispersion energy (DFT-D) [4] and modified MP2 which scaling of spin pair correlation [5]. DFT-D results are in good

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

Vibrational investigation on FT-IR and FT-Raman spectra, IR intensity, Raman activity, peak resemblance, ideal estimation, standard deviation of computed frequencies analyses and electronic structure on 3-methyl-1,2-butadiene using HF and DFT (LSDA/B3LYP/B3PW91) calculations.

PubMed

Ramalingam, S; Jayaprakash, A; Mohan, S; Karabacak, M

2011-11-01

FT-IR and FT-Raman (4000-100 cm(-1)) spectral measurements of 3-methyl-1,2-butadiene (3M12B) have been attempted in the present work. Ab-initio HF and DFT (LSDA/B3LYP/B3PW91) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, IR intensities and Raman activities. Complete vibrational assignments on the observed spectra are made with vibrational frequencies obtained by HF and DFT (LSDA/B3LYP/B3PW91) at 6-31G(d,p) and 6-311G(d,p) basis sets. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The potential energy distribution (PED) corresponding to each of the observed frequencies are calculated which confirms the reliability and precision of the assignment and analysis of the vibrational fundamentals modes. The oscillation of vibrational frequencies of butadiene due to the couple of methyl group is also discussed. A study on the electronic properties such as HOMO and LUMO energies, were performed by time-dependent DFT (TD-DFT) approach. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties of the title compound at different temperatures reveal the correlations between standard heat capacities (C) standard entropies (S), and standard enthalpy changes (H). Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.

27ps DFT Molecular Dynamics Simulation of a-maltose: A Reduced Basis Set Study.

USDA-ARS?s Scientific Manuscript database

DFT molecular dynamics simulations are time intensive when carried out on carbohydrates such as alpha-maltose, requiring up to three or more weeks on a fast 16-processor computer to obtain just 5ps of constant energy dynamics. In a recent publication [1] forces for dynamics were generated from B3LY...

Highly efficient regioselective synthesis, spectroscopic characterizations and DFT calculations of novel hydroxymethylated 1,4-disubstituted-1,2,3-triazole-based sulfonamides

NASA Astrophysics Data System (ADS)

Taheri, Elmira; Mirjafary, Zohreh; Saeidian, Hamid

2018-04-01

The novel hydroxymethylated 1,4-disubstituted-1,2,3-triazole-based sulfonamides were synthesized in excellent yields and high regioselectivity via a one-pot, two-step, three-component reaction of N-propargylsulfonamides, sodium azide, and epoxide derivatives under green conditions. Green and mild reaction condition, commercially readily available and inexpensive starting materials, wide scope and easy work-up are the key features of the present method. The Li+ and Na+ ion affinities of the model structure have been also investigated by density functional theory (DFT) studies to find the applicability of these products as ligand in coordination chemistry.

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

Water adsorption on a copper formate paddlewheel model of CuBTC: A comparative MP2 and DFT study

NASA Astrophysics Data System (ADS)

Toda, Jordi; Fischer, Michael; Jorge, Miguel; Gomes, José R. B.

2013-11-01

Simultaneous adsorption of two water molecules on open metal sites of the HKUST-1 metal-organic framework (MOF), modeled with a Cu2(HCOO)4 cluster, was studied by means of density functional theory (DFT) and second-order Moller-Plesset (MP2) approaches together with correlation consistent basis sets. Experimental geometries and MP2 energetic data extrapolated to the complete basis set limit were used as benchmarks for testing the accuracy of several different exchange-correlation functionals in the correct description of the water-MOF interaction. M06-L and some LC-DFT methods arise as the most appropriate in terms of the quality of geometrical data, energetic data and computational resources needed.

Raman spectra and DFT calculations for botryococcene and methylsqualene hydrocarbons from the B race of the green microalga Botryococcus braunii

NASA Astrophysics Data System (ADS)

Tatli, Mehmet; Chun, Hye Jin; Camp, Charles H.; Li, Jingting; Cicerone, Marcus T.; Shih, Wei-Chuan; Laane, Jaan; Devarenne, Timothy P.

2017-11-01

Botryococcus braunii, a green colonial microalga, is a prodigious producer of liquid hydrocarbon oils that can be used as renewable feedstocks for producing combustion engine fuels. The B race of B. braunii mainly produces the triterpene hydrocarbons known as botryococcenes, which have over twenty known structures. Minor hydrocarbons in the B race include the triterpene methylsqualenes. Here we report an examination of the molecular structure for ten botryococcenes and five methylsqualenes using Raman spectroscopy and density functional theory (DFT) calculations in an effort to distinguish between these structurally similar molecules by spectroscopic approaches. The DFT calculations show that these molecules have between 243 and 271 vibrational frequencies. A comparison of the experimental Raman spectroscopy and DFT calculations indicates several spectral regions such as those for ν(Cdbnd C) stretching, CH2/CH3 bending, and ring bending can be used to distinguish between these molecules. In an extension of this analysis, a broadband coherent anti-Stokes Raman spectroscopy (BCARS) analysis was used to clearly distinguish between several botryococcenes isomers.

Connection between the regular approximation and the normalized elimination of the small component in relativistic quantum theory

NASA Astrophysics Data System (ADS)

Filatov, Michael; Cremer, Dieter

2005-02-01

The regular approximation to the normalized elimination of the small component (NESC) in the modified Dirac equation has been developed and presented in matrix form. The matrix form of the infinite-order regular approximation (IORA) expressions, obtained in [Filatov and Cremer, J. Chem. Phys. 118, 6741 (2003)] using the resolution of the identity, is the exact matrix representation and corresponds to the zeroth-order regular approximation to NESC (NESC-ZORA). Because IORA (=NESC-ZORA) is a variationally stable method, it was used as a suitable starting point for the development of the second-order regular approximation to NESC (NESC-SORA). As shown for hydrogenlike ions, NESC-SORA energies are closer to the exact Dirac energies than the energies from the fifth-order Douglas-Kroll approximation, which is much more computationally demanding than NESC-SORA. For the application of IORA (=NESC-ZORA) and NESC-SORA to many-electron systems, the number of the two-electron integrals that need to be evaluated (identical to the number of the two-electron integrals of a full Dirac-Hartree-Fock calculation) was drastically reduced by using the resolution of the identity technique. An approximation was derived, which requires only the two-electron integrals of a nonrelativistic calculation. The accuracy of this approach was demonstrated for heliumlike ions. The total energy based on the approximate integrals deviates from the energy calculated with the exact integrals by less than 5×10-9hartree units. NESC-ZORA and NESC-SORA can easily be implemented in any nonrelativistic quantum chemical program. Their application is comparable in cost with that of nonrelativistic methods. The methods can be run with density functional theory and any wave function method. NESC-SORA has the advantage that it does not imply a picture change.

Electronic structure and equation of state of Sm2Co17 from first-principles DFT+ U

NASA Astrophysics Data System (ADS)

Huang, Patrick; Butch, Nicholas P.; Jeffries, Jason R.; McCall, Scott K.

2013-03-01

Rare-earth intermetallics have important applications as permanent magnet materials, and the rational optimization of their properties would benefit greatly from guidance from ab initio modeling. However, these systems are particularly challenging for current electronic structure methods. Here, we present an ab initio study of the prototype material Sm2Co17 and related compounds, using density functional theory with a Hubbard correction for the Sm 4 f-electrons (DFT+ U method) and ultrasoft pseudopotentials. The Hubbard U parameter is derived from first principles [Cococcioni and de Gironcoli, PRB 71, 035105 (2005)], not fit to experiment. Our calculations are in good agreement with recent photoemission measurements at ambient pressure and the equation of state up to 40 GPa, thus supporting the validity of our DFT+ U model. Prepared by LLNL under Contract DE-AC52-07NA27344.

Synthesis, X-ray diffraction method, spectroscopic characterization (FT-IR, 1H and 13C NMR), antimicrobial activity, Hirshfeld surface analysis and DFT computations of novel sulfonamide derivatives

NASA Astrophysics Data System (ADS)

Demircioğlu, Zeynep; Özdemir, Fethi Ahmet; Dayan, Osman; Şerbetçi, Zafer; Özdemir, Namık

2018-06-01

Synthesized compounds of N-(2-aminophenyl)benzenesulfonamide 1 and (Z)-N-(2-((2-nitrobenzylidene)amino)phenyl)benzenesulfonamide 2 were characterized by antimicrobial activity, FT-IR, 1H and 13C NMR. Two new Schiff base ligands containing aromatic sulfonamide fragment of (Z)-N-(2-((3-nitrobenzylidene)amino)phenyl)benzenesulfonamide 3 and (Z)-N-(2-((4-nitrobenzylidene)amino)phenyl)benzenesulfonamide 4 were synthesized and investigated by spectroscopic techniques including 1H and 13C NMR, FT-IR, single crystal X-ray diffraction, Hirshfeld surface, theoretical method analyses and by antimicrobial activity. The molecular geometry obtained from the X-ray structure determination was optimized Density Functional Theory (DFT/B3LYP) method with the 6-311++G(d,p) basis set in ground state. From the optimized geometry of the molecules of 3 and 4, the geometric parameters, vibrational wavenumbers and chemical shifts were computed. The optimized geometry results, which were well represented the X-ray data, were shown that the chosen of DFT/B3LYP 6-311G++(d,p) was a successful choice. After a successful optimization, frontier molecular orbitals, chemical activity, non-linear optical properties (NLO), molecular electrostatic mep (MEP), Mulliken population method, natural population analysis (NPA) and natural bond orbital analysis (NBO), which cannot be obtained experimentally, were calculated and investigated.

De(side chain) model of epothilone: bioconformer interconversions DFT study.

PubMed

Rusinska-Roszak, Danuta; Lozynski, Marek

2009-07-01

Using ab initio methods, we have studied conformations of the de(sidechain)de(dioxy)difluoroepothilone model to quantify the effect of stability change between the exo and endo conformers of the epoxy ring. The DFT minimization of the macrolactone ring reveals four low energy conformers, although MP2 predicted five stable structures. The model tested with DFT hybride functional (B3LYP/6-31+G(d,p)) exhibits the global minimum for one of the exo forms (C), experimentally observed in the solid state, but unexpectedly with the MP2 electron correlation method for the virtual endo form (W). Using the QST3 technique, several pathways were found for the conversion of the low energy conformers to the other low energy exo representatives, as well as within the endo analog subset. The potential energy relationships obtained for several exo forms suggest a high conformational mobility between three, experimentally observed, conformers. The high rotational barrier, however, excludes direct equilibrium with experimental EC-derived endo form S. The highest calculated transition state for the conversion of the most stable exo M interligand to the endo S form is approximately a 28 kcal/mol above the energy of the former. The two-step interconversion of the exo H conformer to the endo S requires at least 28 kcal/mol. Surprisingly, we found that the transition state energy of the H form to the virtual endo W has the acceptable value of about 9 kcal/mol and the next energy barrier for free interconversion of endo W to endo S is 13 kcal/mol.

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.

Spectroscopic and DFT study of solvent effects on the electronic absorption spectra of sulfamethoxazole in neat and binary solvent mixtures

NASA Astrophysics Data System (ADS)

Almandoz, M. C.; Sancho, M. I.; Blanco, S. E.

2014-01-01

The solvatochromic behavior of sulfamethoxazole (SMX) was investigated using UV-vis spectroscopy and DFT methods in neat and binary solvent mixtures. The spectral shifts of this solute were correlated with the Kamlet and Taft parameters (α, β and π*). Multiple lineal regression analysis indicates that both specific hydrogen-bond interaction and non specific dipolar interaction play an important role in the position of the absorption maxima in neat solvents. The simulated absorption spectra using TD-DFT methods were in good agreement with the experimental ones. Binary mixtures consist of cyclohexane (Cy)-ethanol (EtOH), acetonitrile (ACN)-dimethylsulfoxide (DMSO), ACN-dimethylformamide (DMF), and aqueous mixtures containing as co-solvents DMSO, ACN, EtOH and MeOH. Index of preferential solvation was calculated as a function of solvent composition and non-ideal characteristics are observed in all binary mixtures. In ACN-DMSO and ACN-DMF mixtures, the results show that the solvents with higher polarity and hydrogen bond donor ability interact preferentially with the solute. In binary mixtures containing water, the SMX molecules are solvated by the organic co-solvent (DMSO or EtOH) over the whole composition range. Synergistic effect is observed in the case of ACN-H2O and MeOH-H2O, indicating that at certain concentrations solvents interact to form association complexes, which should be more polar than the individual solvents of the mixture.

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.

An EQT-based cDFT approach for thermodynamic properties of confined fluid mixtures

NASA Astrophysics Data System (ADS)

Motevaselian, M. H.; Aluru, N. R.

2017-04-01

We present an empirical potential-based quasi-continuum theory (EQT) to predict the structure and thermodynamic properties of confined fluid mixtures. The central idea in the EQT is to construct potential energies that integrate important atomistic details into a continuum-based model such as the Nernst-Planck equation. The EQT potentials can be also used to construct the excess free energy functional, which is required for the grand potential in the classical density functional theory (cDFT). In this work, we use the EQT-based grand potential to predict various thermodynamic properties of a confined binary mixture of hydrogen and methane molecules inside graphene slit channels of different widths. We show that the EQT-cDFT predictions for the structure, surface tension, solvation force, and local pressure tensor profiles are in good agreement with the molecular dynamics simulations. Moreover, we study the effect of different bulk compositions and channel widths on the thermodynamic properties. Our results reveal that the composition of methane in the mixture can significantly affect the ordering of molecules and thermodynamic properties under confinement. In addition, we find that graphene is selective to methane molecules.

Experimental (X-ray, FT-IR and UV-vis spectra) and theoretical methods (DFT study) of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol.

PubMed

Demircioğlu, Zeynep; Albayrak, Çiğdem; Büyükgüngör, Orhan

2014-07-15

A suitable single crystal of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol, formulated as C15H15N1O2, reveals that the structure is adopted to its E configuration about the azomethine C=N double bond. The compound adopts a enol-imine tautomeric form with a strong intramolecular O-H⋯N hydrogen bond. The single crystal X-ray diffraction analysis at 296K crystallizes in the monoclinic space group P21/c with a = 13.4791(11) Å, b = 6.8251(3) Å, c = 18.3561(15) Å, α = 90°, β = 129.296(5)°, γ = 90° and Z = 4. Comprehensive theoretical and experimental structural studies on the molecule have been carried out by FT-IR and UV-vis spectrometry. Optimized molecular structure and harmonic vibrational frequencies have been investigated by DFT/B3LYP method with 6-31G(d,p) basis set. Stability of the molecule, hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed by using natural bond orbital (NBO) analysis. Electronic structures were discussed by TD-DFT method and the relocation of the electron density were determined. The energetic behavior of the title compound has been examined in solvent media using polarizable continuum model (PCM). Molecular electrostatic potential (MEP), Mulliken population method and natural population analysis (NPA) have been studied. Nonlinear optical (NLO) properties were also investigated. In addition, frontier molecular orbitals analysis have been performed from the optimized geometry. An ionization potential (I), electron affinity (A), electrophilicity index (ω), chemical potential (μ), electronegativity (χ), hardness (η), and softness (S), have been investigated. Copyright © 2014 Elsevier B.V. All rights reserved.

DFT investigations of phosphotriesters hydrolysis in aqueous solution: a model for DNA single strand scission induced by N-nitrosoureas.

PubMed

Liu, Tingting; Zhao, Lijiao; Zhong, Rugang

2013-02-01

DNA phosphotriester adducts are common alkylation products of DNA phosphodiester moiety induced by N-nitrosoureas. The 2-hydroxyethyl phosphotriester was reported to hydrolyze more rapidly than other alkyl phosphotriesters both in neutral and in alkaline conditions, which can cause DNA single strand scission. In this work, DFT calculations have been employed to map out the four lowest activation free-energy profiles for neutral and alkaline hydrolysis of triethyl phosphate (TEP) and diethyl 2-hydroxyethyl phosphate (DEHEP). All the hydrolysis pathways were illuminated to be stepwise involving an acyclic or cyclic phosphorane intermediate for TEP or DEHEP, respectively. The rate-limiting step for all the hydrolysis reactions was found to be the formation of phosphorane intermediate, with the exception of DEHEP hydrolysis in alkaline conditions that the decomposition process turned out to be the rate-limiting step, owing to the extraordinary low formation barrier of cyclic phosphorane intermediate catalyzed by hydroxide. The rate-limiting barriers obtained for the four reactions are all consistent with the available experimental information concerning the corresponding hydrolysis reactions of phosphotriesters. Our calculations performed on the phosphate triesters hydrolysis predict that the lower formation barriers of cyclic phosphorane intermediates compared to its acyclic counter-part should be the dominant factor governing the hydrolysis rate enhancement of DEHEP relative to TEP both in neutral and in alkaline conditions.

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.

Conformational stability, vibrational spectra, molecular structure, NBO and HOMO-LUMO analysis of 5-nitro-2-furaldehyde oxime based on DFT calculations.

PubMed

Arivazhagan, M; Jeyavijayan, S; Geethapriya, J

2013-03-01

The FTIR and FT-Raman spectra of 5-nitro-2-furaldehyde oxime (NFAO) have been recorded in the regions 4000-400 cm(-1) and 3500-50 cm(-1), respectively. The total energies of different conformations have been obtained from DFT (B3LYP) with 6-311++G(d,p) basis set calculations. The computational results identify the most stable conformer of NFAO as the C1 form. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of the fundamental modes of the compound were carried out. The optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, were calculated by density functional theory (DFT/B3LYP) method with 6-31+G(d,p) and 6-311++G(d,p) basis sets. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared and Raman spectra of NFAO is also reported based on total energy distribution (TED). Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. Besides, molecular electrostatic potential (MEP), HOMO and LUMO analysis, and several thermodynamic properties were performed by the DFT method. Mulliken's net charges have been calculated and compared with the natural atomic charges. Ultraviolet-visible spectrum of the title molecule has also been calculated using TD-DFT method. Copyright © 2012 Elsevier B.V. All rights reserved.

Study of gas-phase O-H bond dissociation enthalpies and ionization potentials of substituted phenols - Applicability of ab initio and DFT/B3LYP methods

NASA Astrophysics Data System (ADS)

Klein, Erik; Lukeš, Vladimír

2006-11-01

In this paper, the study of phenol and 37 compounds representing various ortho-, para-, and meta-substituted phenols is presented. Molecules and their radical structures were studied using ab initio methods with inclusion of correlation energy and DFT in order to calculate the O-H bond dissociation enthalpies (BDEs) and vertical ionization potentials (IPs). Calculated BDEs and IPs were compared with available experimental values to ascertain the suitability of used methods, especially for the description of the substituent induced changes in BDE and IP. MP2, MP3, and MP4 methods do not give reliable results, since they significantly underestimate substituent induced changes in BDE and do not reflect distinct effect of substituents related to para and meta position correctly. DFT/B3LYP method reflects the effect of substituents on BDE satisfactorily, though ΔBDEs are in narrower range than experimental values. BDE of phenol was calculated also using CCSD(T) method in various basis sets. Both, DFT and HF methods describe the effect of substituents on IP identically. However, DFT considerably underestimates individual values. HF method gives IPs in very good agreement with experimental data. Obtained results show that dependences of BDEs and IPs on Hammett constants of the substituents are linear. Linearity of DFT BDE vs. IP dependence is even better than the dependences on Hammett constants and obtained equations allow estimating of O-H BDEs of meta- and para-substituted phenols from calculated IPs.

DFT Studies on Interaction between Lanthanum and Hydroxyamide

NASA Astrophysics Data System (ADS)

Pati, Anindita; Kundu, T. K.; Pal, Snehanshu

2018-03-01

Extraction and separation of individual rare earth elements has been a challenge as they are chemically very similar. Solvent extraction is the most suitable way for extraction of rare earth elements. Acidic, basic, neutral, chelating are the major classes of extractants for solvent extraction of rare earth elements. The coordination complex of chelating extractants is very selective with positively charged metal ion. Hence they are widely used. Hydroxyamide is capable of forming chelates with metal cations. In this present study interactions of hydroxyamide ligand with lanthanum have been investigated using density functional theory (DFT). Two different functional such as raB97XD and B3LYP are applied along with 6-31+G(d,p) basis set for carbon, nitrogen, hydrogen and SDD basis set for lanthanum. Stability of formed complexes has been evaluated based on calculated interaction energies and solvation energies. Frontier orbital (highest occupied molecular orbital or HOMO and lowest unoccupied molecular orbital or LUMO) energies of the molecule have also been calculated. Electronegativity, chemical hardness, chemical softness and chemical potential are also determined for these complexes to get an idea about the reactivity. From the partial charge distribution it is seen that oxygen atoms in hydroxyamide have higher negative charge. The double bonded oxygen atom present in the hydroxyamide structure has higher electron density and so it forms bond with lanthanum but the singly bonded oxygen atom in the hydroxyamide structure is weaker donor atom and so it is less available for interaction with lanthanum.

Thermodynamics, kinetics, and catalytic effect of dehydrogenation from MgH2 stepped surfaces and nanocluster: a DFT study

NASA Astrophysics Data System (ADS)

Reich, Jason; Wang, Linlin; Johnson, Duane

2013-03-01

We detail the results of a Density Functional Theory (DFT) based study of hydrogen desorption, including thermodynamics and kinetics with(out) catalytic dopants, on stepped (110) rutile and nanocluster MgH2. We investigate competing configurations (optimal surface and nanoparticle configurations) using simulated annealing with additional converged results at 0 K, necessary for finding the low-energy, doped MgH2 nanostructures. Thermodynamics of hydrogen desorption from unique dopant sites will be shown, as well as activation energies using the Nudged Elastic Band algorithm. To compare to experiment, both stepped structures and nanoclusters are required to understanding and predict the effects of ball milling. We demonstrate how these model systems relate to the intermediary sized structures typically seen in ball milling experiments.

Europium, uranyl, and thorium-phenanthroline amide complexes in acetonitrile solution: an ESI-MS and DFT combined investigation.

PubMed

Xiao, Cheng-Liang; Wang, Cong-Zhi; Mei, Lei; Zhang, Xin-Rui; Wall, Nathalie; Zhao, Yu-Liang; Chai, Zhi-Fang; Shi, Wei-Qun

2015-08-28

The tetradentate N,N'-diethyl-N,N'-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen) ligand with hard-soft donor atoms has been demonstrated to be promising for the group separation of actinides from highly acidic nuclear wastes. To identify the formed complexes of this ligand with actinides and lanthanides, electrospray ionization mass spectrometry (ESI-MS) combined with density functional theory (DFT) calculations was used to probe the possible complexation processes. The 1 : 2 Eu-L species ([EuL2(NO3)](2+)) can be observed in ESI-MS at low metal-to-ligand ([M]/[L]) ratios, whereas the 1 : 1 Eu-L species ([EuL(NO3)2](+)) can be observed when the [M]/[L] ratio is higher than 1.0. However, ([UO2L(NO3)](+)) is the only detected species for the uranyl complexes. The [ThL2(NO3)2](2+) species can be observed at low [M]/[L] ratios; the 1 : 2 species ([ThL2(NO3)](3+)) and a new 1 : 1 species ([ThL(NO3)3](+)) can be detected at high [M]/[L] ratios. Collision-induced dissociation (CID) results showed that Et-Tol-DAPhen ligands can coordinate strongly with metal ions, and the coordination moieties remain intact under CID conditions. Natural bond orbital (NBO), molecular electrostatic potential (MEP), electron localization function (ELF), atoms in molecules (AIM) and molecular orbital (MO) analyses indicated that the metal-ligand bonds of the actinide complexes exhibited more covalent character than those of the lanthanide complexes. In addition, according to thermodynamic analysis, the stable cationic M-L complexes in acetonitrile are found to be in good agreement with the ESI-MS results.

Levofloxacin capped Ag-nanoparicles: A new highly selective sensor for cations under joint experimental and DFT investigation

NASA Astrophysics Data System (ADS)

Mondal Roy, Sutapa; Roy, Debesh Ranjan

2017-05-01

A very new and alternate function of an antibiotic drug levofloxacin (Lv), as a highly selective, colorimetric turn-OFF/turn-ON chemosensor for metal-ions Hg2+ and Fe3+, has been reported in this study. An extremely easy, very less time consuming, economical one-pot method of synthesis has been developed for the production of silver nanoparticles (AgNPs). The AgNPs that are stabilized and surface functionalized by Lv. Functionalization of AgNPs by antibiotic drug Lv has been thoroughly confirmed using FTIR spectrophotometry. Two carbonyl oxygen moieties, one belongs to the pyridine oxygen group and another one from the carboxylate oxygen group of Lv together form the binding site over the nanoparticle surface. The Lv-AgNPs system has shown naked eye detectable colour change, as well as significant change via both UV-Vis and fluorescence spectroscopy. The limits of detection (LODs) are predicted to be 6.86 × 10-8 M for Hg2+ and 2.52 × 10-9 M for Fe3+ using UV-Vis spectroscopy and 2.35 × 10-9 M for Fe3+ using fluorescence spectroscopy. UV-Vis spectroscopy, fluorescence spectroscopy, FTIR, TEM, DLS etc. have been used for the physico-chemical characterization of Lv-AgNPs system and the nanoparticle mediated sensing process. Detailed experimental and theoretical studies employing FTIR spectrophotometry and density functional theory (DFT) studies have been used for the elucidation of drug-nanoparticle based sensing mechanism. It is also demonstrated that the Lv-AgNPs system can show real time application using Test-Paper Kit to establish the drug-nanoparticle assembly as a potential colorimetric turn-OFF/turn-ON sensing system for Hg2+ and Fe3+ respectively.

Adsorption performance of Rh decorated SWCNT upon SF6 decomposed components based on DFT method

NASA Astrophysics Data System (ADS)

Zhang, Xiaoxing; Cui, Hao; Dong, Xingchen; Chen, Dachang; Tang, Ju

2017-10-01

Transition metal decorated carbon nanotubes (CNTs) applied in the field of gas adsorption and storage have in recent years accepted considerable attentions because of their superior adsorbing performance. In electrical engineering, they are employed as adsorbents to remove the decomposed products of SF6 caused by partial discharge, for guaranteeing the insulation status of gas insulation switchgear (GIS). In this paper, Rh doped SWCNT is introduced to investigate its adsorption properties towards typical gases of SF6 based on density functional theory (DFT) method. Both single and double molecules adsorbing systems were performed to investigate the adsorption ability of proposed material. Results indicate that Rh-CNT, which has strong interaction with defined gas molecules, is a promising material for SF6 decompositions adsorption especially SO2 and SOF2 that exhibit topmost sensitivity to the modified surface. Therefore, we suggest the Rh-CNT to be an adsorbent to be applied in GIS for guaranteeing the operation state of such devices and even to be exploited as gas sensor to evaluate the insulation state of the power system. Our calculations would provide experimentalist with a first insight into physicochemical properties of this material.

Highly-Efficient Charge Separation and Polaron Delocalization in Polymer-Fullerene Bulk-Heterojunctions: A Comparative Multi-Frequency EPR & DFT Study

PubMed Central

Niklas, Jens; Mardis, Kristy L.; Banks, Brian P.; Grooms, Gregory M.; Sperlich, Andreas; Dyakonov, Vladimir; Beaupré, Serge; Leclerc, Mario; Xu, Tao; Yu, Luping; Poluektov, Oleg G.

2016-01-01

delocalization of the positive polaron on the polymer donor is an important reason for the efficient charge separation in bulk heterojunction systems as it minimizes the wasteful process of charge recombination. The combination of advanced EPR spectroscopy and DFT is a powerful approach for investigation of light-induced charge dynamics in organic photovoltaic materials. PMID:23670645

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.

Mechanistic Investigation of Molybdate-Catalysed Transfer Hydrodeoxygenation.

PubMed

Larsen, Daniel B; Petersen, Allan R; Dethlefsen, Johannes R; Teshome, Ayele; Fristrup, Peter

2016-11-07

The molybdate-catalysed transfer hydrodeoxygenation (HDO) of benzyl alcohol to toluene driven by oxidation of the solvent isopropyl alcohol to acetone has been investigated by using a combination of experimental and computational methods. A Hammett study that compared the relative rates for the transfer HDO of five para-substituted benzylic alcohols was carried out. Density-functional theory (DFT) calculations suggest a transition state with significant loss of aromaticity contributes to the lack of linearity observed in the Hammett study. The transfer HDO could also be carried out in neat PhCH 2 OH at 175 °C. Under these conditions, PhCH 2 OH underwent disproportionation to yield benzaldehyde, toluene, and significant amounts of bibenzyl. Isotopic-labelling experiments (using PhCH 2 OD and PhCD 2 OH) showed that incorporation of deuterium into the resultant toluene originated from the α position of benzyl alcohol, which is in line with the mechanism suggested by the DFT study. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoinduced dynamics to photoluminescence in Ln3+ (Ln = Ce, Pr) doped β-NaYF4 nanocrystals computed in basis of non-collinear spin DFT with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Han, Yulun; Vogel, Dayton J.; Inerbaev, Talgat M.; May, P. Stanley; Berry, Mary T.; Kilin, Dmitri S.

2018-03-01

In this work, non-collinear spin DFT + U approaches with spin-orbit coupling (SOC) are applied to Ln3+ doped β-NaYF4 (Ln = Ce, Pr) nanocrystals in Vienna ab initio Simulation Package taking into account unpaired spin configurations using the Perdew-Burke-Ernzerhof functional in a plane wave basis set. The calculated absorption spectra from non-collinear spin DFT + U approaches are compared with that from spin-polarised DFT + U approaches. The spectral difference indicates the importance of spin-flip transitions of Ln3+ ions. Suite of codes for nonadiabatic dynamics has been developed for 2-component spinor orbitals. On-the-fly nonadiabatic coupling calculations provide transition probabilities facilitated by nuclear motion. Relaxation rates of electrons and holes are calculated using Redfield theory in the reduced density matrix formalism cast in the basis of non-collinear spin DFT + U with SOC. The emission spectra are calculated using the time-integrated method along the excited state trajectories based on nonadiabatic couplings.

Spin–orbit DFT with Analytic Gradients and Applications to Heavy Element Compounds

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

Zhang, Zhiyong

We have implemented the unrestricted DFT approach with one-electron spin–orbit operators in the massively parallel NWChem program. Also implemented is the analytic gradient in the DFT approach with spin–orbit interactions. The current capabilities include single-point calculations and geometry optimization. Vibrational frequencies can be calculated numerically from the analytically calculated gradients. The implementation is based on the spin–orbit interaction operator derived from the effective core potential approach. The exchange functionals used in the implementation are functionals derived for non-spin–orbit calculations, including GGA as well as hybrid functionals. Spin–orbit Hartree–Fock calculations can also be carried out. We have applied the spin–orbit DFTmore » methods to the Uranyl aqua complexes. We have optimized the structures and calculated the vibrational frequencies of both (UO2 2+)aq and (UO2 +)aq with and without spin–orbit effects. The effects of the spin–orbit interaction on the structures and frequencies of these two complexes are discussed. We also carried out calculations for Th2, and several low-lying electronic states are calculated. Our results indicate that, for open-shell systems, there are significant effects due to the spin–orbit effects and the electronic configurations with and without spin–orbit interactions could change due to the occupation of orbitals of larger spin–orbit interactions.« 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.

DFT Study of PH3 Physisorption and Chemisorptions on Boron Nitride Nanotubes

NASA Astrophysics Data System (ADS)

Rakhshi, Mahdi; Mohsennia, Mohsen; Rasa, Hossein

2018-03-01

The adsorption of PH3 molecules on the NiB,N-doped(4,4) and (5,5) BNNTS surfaces has been investigated using density functional theory (DFT). The adsorption energies, geometric and electronic structures of the adsorbed systems were studied to judge the possible application of NiB,N-doped BNNTS in PH3 monitoring systems. Our calculated results showed that NiB,N-doped BNNTS had much higher adsorption energy and shorter binding distances than pure BNNTS owning to chemisorptions of the PH3 molecule. The obtained density of states (DOS) and frontier orbitals demonstrated that the orbital hybridization was obvious between the PH3 molecule and NiB,N-doped BNNTS. However, due to weak physisorption according to the total electron density maps, there was no evidence for hybridization between PH3 molecule and pure BNNTS. It was shown that after doping of Ni atom, the primary symmetry of BNNTS decreased which enhanced the chemical activity of BNNTS towards PH3 molecules. According to the obtained results, we highlight the high potential application of NiB,N-doped BNNTS in the design and fabrication of PH3 sensing devices.

Thz Spectroscopy and DFT Modeling of Intermolecular Vibrations in Hydrophobic Amino Acids

NASA Astrophysics Data System (ADS)

Williams, michael R. C.; Aschaffenburg, Daniel J.; Schmuttenmaer, Charles A.

2013-06-01

Vibrations that involve intermolecular displacements occur in molecular crystals at frequencies in the 0.5-5 THz range (˜15-165 cm^{-1}), and these motions are direct indicators of the interaction potential between the molecules. The intermolecular potential energy surface of crystalline hydrophobic amino acids is inherently interesting simply because of the wide variety of forces (electrostatic, dipole-dipole, hydrogen-bonding, van der Waals) that are present. Furthermore, an understanding of these particular interactions is immediately relevant to important topics like protein conformation and pharmaceutical polymorphism. We measured the low-frequency absorption spectra of several polycrystalline hydrophobic amino acids using THz time-domain spectroscopy, and in addition we carried out DFT calculations using periodic boundary conditions and an exchange-correlation functional that accounts for van der Waals dispersion forces. We chose to investigate a series of similar amino acids with closely analogous unit cells (leucine, isoleucine, and allo-isoleucine, in racemic or pseudo-racemic mixtures). This allows us to consider trends in the vibrational spectra as a function of small changes in molecular arrangement and/or crystal geometry. In this way, we gain confidence that peak assignments are not based on serendipitous similarities between calculated and observed features.

Synthesis, crystal structure and DFT studies of a dual fluorescent ketamine: Structural changes in the ground and excited states

NASA Astrophysics Data System (ADS)

Latha, V.; Balakrishnan, C.; Neelakantan, M. A.

2015-07-01

A fluorescent probe 2Z,2‧Z-3,3‧-(4,4‧-methylenebis(4,1-phenylene) bis(azanediyl))bis (1,3-diphenylprop-2-en-1-one) (L) was synthesized and characterized by IR, 1H NMR, ESI-mass, UV-visible and fluorescence spectral techniques. The single crystal analysis illustrates the existence of L in ketamine form. The crystal structure is stabilized by intramolecular and intermolecular hydrogen bonding. The thermal stability of L was studied by TG analysis. The fluorescence spectrum of L shows dual emission, and is due to excited state intramolecular proton transfer (ESIPT) process. This is supported by the high Stokes shift value. Electronic structure calculations of L in the ground and excited state have been carried out using DFT and TD-DFT at B3LYP/6-31G (d,p) level, respectively. The vibrational spectrum was computed at this level and compared with experimental values. Major orbital contributions for the electronic transitions were assigned with the help of TD-DFT. The changes in the Mulliken charge, bond lengths and bond angles between the ground and excited states of the tautomers demonstrate that twisted intramolecular charge transfer (TICT) process occurs along with ESIPT in the excited state.

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

FT-IR and DFT study of lemon peel

NASA Astrophysics Data System (ADS)

Berezin, K. V.; Likhter, A. M.; Shagautdinova, I. T.; Chernavina, M. L.; Novoselova, A. V.

2017-03-01

Experimental FT-IR spectra of lemon peel are registered in the 650 - 3800 cm-1 range. The influence of peel artificial and natural dehydration on its vibrational spectrum is studied. The colored outer surface of lemon peel is proved not to have a significant impact on FT-IR spectrum. It is determined that only dehydration processes affect the FT-IR vibrational spectrum of the peel when a lemon is stored for 28 days under natural laboratory conditions. Polymer molecule models for dietary fibers, such as cellulose, hemicellulose, pectin, lignin, as well as hesperidin - flavonoid glycoside, and free moisture cluster are developed within the framework of DFT/B3LYP/6-31G(d) theoretical method. By implementing supramolecular approach, modeling of the vibrational FT-IR spectrum of lemon peel is carried out and its detailed theoretical interpretation is presented.

Synthesis, spectroscopic and TD-DFT quantum mechanical study of azo-azomethine dyes. A laser induced trans-cis-trans photoisomerization cycle

NASA Astrophysics Data System (ADS)

Georgiev, Anton; Kostadinov, Anton; Ivanov, Deyan; Dimov, Deyan; Stoyanov, Simeon; Nedelchev, Lian; Nazarova, Dimana; Yancheva, Denitsa

2018-03-01

This paper describes the synthesis, spectroscopic characterization and quantum mechanical calculations of three azo-azomethine dyes. The dyes were synthesized via condensation reaction between 4-(dimethylamino)benzaldehyde and three different 4-aminobenzene azo dyes. Quantum chemical calculations on the optimized molecular geometry and electron densities of the trans (E) and cis (Z) isomers and their vibrational frequencies have been computed by using DFT/B3LYP density-functional theory with 6-311 ++G(d,p) basis set in vacuo. The thermodynamic parameters such as total electronic energy E (RB3LYP), enthalpy H298 (sum of electronic and thermal enthalpies), free Gibbs energy G298 (sum of electronic and thermal free Gibbs energies) and dipole moment μ were computed for trans (E) and cis (Z) isomers in order to estimate the ΔEtrans → cis, Δμtrans → cis,ΔHtrans → cis, ΔGtrans → cis and ΔStrans → cis values. After molecular geometry optimization the electronic spectra have been obtained by TD-DFT calculations at same basis set and correlated with the spectra of vapour deposited nanosized films of the dyes. The NBO analysis was performed in order to understand the intramolecular charge transfer and energy of resonance stabilization. Solvatochromism was investigated by UV-VIS spectroscopy in five different organic solvents with increasing polarity. The dynamic photoisomerization experiments have been performed in DMF by pump lasers λ = 355 nm (mostly E → Z) and λ = 491 nm (mostly Z → E) in spectral region 300 nm - 800 nm at equal concentrations and times of illumination in order to investigate the photodynamical trans-cis-trans properties of the sbnd CHdbnd Nsbnd and sbnd Ndbnd Nsbnd chromophore groups of the dyes.

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

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.

DFT Studies of SN2 Dechlorination of Polychlorinated Biphenyls.

PubMed

Krzemińska, Agnieszka; Paneth, Piotr

2016-06-21

Nucleophilic dechlorination of all 209 PCBs congeners by ethylene glycol anion has been studied theoretically at the DFT level. The obtained Gibbs free energies of activation are in the range 7-22 kcal/mol. The reaction Gibbs free energies indicate that all reactions are virtually irreversible. Due to geometric constrains these reactions undergo rather untypical attack with attacking oxygen atom being nearly perpendicular to the attacked C-Cl bond. The most prone to substitution are chlorine atoms that occupy ortho- (2, 2', 6, 6') positions. These results provide extensive information on the PEG/KOH dependent PCBs degradation. They can also be used in further developments of reaction class transition state theory (RC-TST) for description of complex reactive systems encountered for example in combustion processes.

Proton Affinities of Anionic Bases:  Trends Across the Periodic Table, Structural Effects, and DFT Validation.

PubMed

Swart, Marcel; Bickelhaupt, F Matthias

2006-03-01

We have carried out an extensive exploration of the gas-phase basicity of archetypal anionic bases across the periodic system using the generalized gradient approximation of density functional theory (DFT) at BP86/QZ4P//BP86/TZ2P. First, we validate DFT as a reliable tool for computing proton affinities and related thermochemical quantities:  BP86/QZ4P//BP86/TZ2P is shown to yield a mean absolute deviation of 1.6 kcal/mol for the proton affinity at 0 K with respect to high-level ab initio benchmark data. The main purpose of this work is to provide the proton affinities (and corresponding entropies) at 298 K of the anionic conjugate bases of all main-group-element hydrides of groups 14-17 and periods 2-6. We have also studied the effect of stepwise methylation of the protophilic center of the second- and third-period bases.

Spectroscopic, Homo-Lumo and NLO studies of tetra fluoro phthalate doped Coumarin crystals using DFT method

NASA Astrophysics Data System (ADS)

Latha, B.; Kumaresan, P.; Nithiyanantham, S.; Sampathkumar, K.

2017-08-01

In the present examination, a methodical study has been done on the development of unadulterated and Coumarin doped Tetrafluoro Phthalate precious stones. Powder X-beam diffraction studies were done and the cross section parameters were computed by minimum square technique in pure and doped crystals. FT-IR, UV-Vis, Thermal, Micro-hardness and Dielectric studies were additionally done for the pure and doped crystals. The tentatively watched FT-IR and FT-Raman groups were allotted to various ordinary methods of the atom. The steadiness and charge delocalization of the particle were likewise concentrations were done by characteristic security orbital (NBO) examination. The HOMO-LUMO energies depict the charge exchange happens inside the particle. Atomic electrostatic potential has been broken down the electronic properties such as excitation energies, oscillator quality, wavelengths and HOMO-LUMO energies were acquired by time-subordinate DFT (TD-DFT) approach. The SHG of pure and doped TFP stones were examined through Nd:YAG Q-exchanged laser.

Function-Space-Based Solution Scheme for the Size-Modified Poisson-Boltzmann Equation in Full-Potential DFT.

PubMed

Ringe, Stefan; Oberhofer, Harald; Hille, Christoph; Matera, Sebastian; Reuter, Karsten

2016-08-09

The size-modified Poisson-Boltzmann (MPB) equation is an efficient implicit solvation model which also captures electrolytic solvent effects. It combines an account of the dielectric solvent response with a mean-field description of solvated finite-sized ions. We present a general solution scheme for the MPB equation based on a fast function-space-oriented Newton method and a Green's function preconditioned iterative linear solver. In contrast to popular multigrid solvers, this approach allows us to fully exploit specialized integration grids and optimized integration schemes. We describe a corresponding numerically efficient implementation for the full-potential density-functional theory (DFT) code FHI-aims. We show that together with an additional Stern layer correction the DFT+MPB approach can describe the mean activity coefficient of a KCl aqueous solution over a wide range of concentrations. The high sensitivity of the calculated activity coefficient on the employed ionic parameters thereby suggests to use extensively tabulated experimental activity coefficients of salt solutions for a systematic parametrization protocol.

DFT-MD simulations of shocked Xenon

NASA Astrophysics Data System (ADS)

Magyar, Rudolph J.; Mattsson, Thomas R.

2009-03-01

Xenon is not only a technologically important element used in laser technologies, jet propulsion and dental anesthesia, but it is also arguably the simplest material in which to study the metal-insulator transition at high pressure. Because of its closed shell electronic configuration, Xenon is often assumed to be chemically inert, interacting almost entirely through the van der Waals interaction, and at liquid density, is typically modeled well using Leonard-Jones potentials. However, such modeling has a limited range of validity as Xenon is known to form compounds at normal conditions and likely exhibits considerably more chemistry at higher densities when hybridization of occupied orbitals becomes significant. In this talk, we present DFT-MD simulations of shocked liquid Xenon with the goal of developing an improved equation of state. The relative importance of the van der Waals interaction compared to other Coulomb interactions is considered, and estimates of the relative accuracy of various density functionals are quantified. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

A first principles investigation of the oxygen adsorption on Zr(0001) surface using cluster expansions

NASA Astrophysics Data System (ADS)

Samin, Adib J.; Taylor, Christopher D.

2017-11-01

The design of corrosion resistant zircalloys is important for a variety of technological applications ranging from medicine to the nuclear industry. Since corrosion resistance is mainly attributed to the formation of a surface oxide layer, developing a detailed understanding of this process may assist in future corrosion resistance design. In this work, we conduct a systematic multi-scale investigation of the early stages of oxide formation. This was accomplished by first using a database of fully relaxed DFT calculations to build a cluster-expansion description of the potential function. The developed potential was reasonably good at predicting DFT energies as evidenced by the cross-validation score of 4.4 meV/site. The effective cluster expansion parameters were indicative of repulsive adsorbate interactions in the adlayer in agreement with the literature. The potential then allowed for a systematic investigation of the oxygen configurations on the Zr(0001) surface via Monte Carlo simulations. The adsorption energy was recorded as a function of coverage and an increasing trend was observed in agreement with DFT predictions and the repulsive nature of interactions in the adlayer. The convex hull diagram was recorded indicating the most stable configuration to occur around a coverage of 0.6 ML. The adsorption isotherm was also recorded and contrasted for two temperatures relevant for different applications.

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.

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.

Theoretical study of zeatin - A plant hormone and potential drug for neural diseases - On the basis of DFT, MP2 and target docking

NASA Astrophysics Data System (ADS)

Liu, Xueping; Bereźniak, Tomasz; Panek, Jarosław Jan; Jezierska-Mazzarello, Aneta

2013-02-01

Zeatin, a cytokinin of the adenine family, originally isolated from Zea mays L., exhibits also bioeffects towards human cells: it is a potent acetylcholinesterase inhibitor and can potentially inhibit amyloid β-protein formation. The role of zeatin in neural disease treatment is yet to be established. This computational study describes a hierarchy of interactions between zeatin and a receptor, a protein from the nodulin family. DFT in hybrid and dispersion-corrected form as well as MP2 approaches were used to derive interaction energies. Docking procedure was employed to investigate the role of selected interaction for anchoring the ligand.

Accurate Induction Energies for Small Organic Molecules. 2. Development and Testing of Distributed Polarizability Models against SAPT(DFT) Energies.

PubMed

Misquitta, Alston J; Stone, Anthony J; Price, Sarah L

2008-01-01

In part 1 of this two-part investigation we set out the theoretical basis for constructing accurate models of the induction energy of clusters of moderately sized organic molecules. In this paper we use these techniques to develop a variety of accurate distributed polarizability models for a set of representative molecules that include formamide, N-methyl propanamide, benzene, and 3-azabicyclo[3.3.1]nonane-2,4-dione. We have also explored damping, penetration, and basis set effects. In particular, we have provided a way to treat the damping of the induction expansion. Different approximations to the induction energy are evaluated against accurate SAPT(DFT) energies, and we demonstrate the accuracy of our induction models on the formamide-water dimer.

Ti Impurity Effect on the Optical Coefficients in 2D Cu2Si: A DFT Study

NASA Astrophysics Data System (ADS)

Nourozi, Bromand; Boochani, Arash; Abdolmaleki, Ahmad; Sartpi, Elmira; Darabi, Pezhman; Naderi, Sirvan

2018-01-01

The electronic and optical properties of 2D Cu2Si and Cu2Si:Ti are investigated based on the density functional theory (DFT) using the FP-LAPW method and GGA approximation. The 2D Cu2Si has metallic and non magnetic properties, whereas adding Ti impurity to its structure changes the electronic behavior to the half-metallic with 3.256μB magnetic moment. The optical transition is not occurred in the infrared and visible area for the 2D Cu2Si in x-direction and by adding Ti atom, the real part of dielectric function in the x-direction, Re (ε(ω))x is reached to a Dirac peak at this energy range. Moreover, the absorption gap tends to zero in x-direction of the 2D Cu2Si:Ti. Supported by Islamic Azad University, Kermanshah branch, Kermanshah, Iran

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.

MP2, DFT-D, and PCM study of the HMB-TCNE complex: Thermodynamics, electric properties, and solvent effects

NASA Astrophysics Data System (ADS)

Kysel, Ondrej; Budzák, Scaronimon; Medveď, Miroslav; Mach, Pavel

Geometry, thermodynamic, and electric properties of the pi-EDA complex between hexamethylbenzene (HMB) and tetracyanoethylene (TCNE) are investigated at the MP2/6-31G* and, partly, DFT-D/6-31G* levels. Solvent effects on the properties are evaluated using the PCM model. Fully optimized HMB-TCNE geometry in gas phase is a stacking complex with an interplanar distance 2.87 × 10-10 m and the corresponding BSSE corrected interaction energy is -51.3 kJ mol-1. As expected, the interplanar distance is much shorter in comparison with HF and DFT results. However the crystal structures of both (HMB)2-TCNE and HMB-TCNE complexes have interplanar distances somewhat larger (3.18 and 3.28 × 10-10 m, respectively) than our MP2 gas phase value. Our estimate of the distance in CCl4 on the basis of PCM solvent effect study is also larger (3.06-3.16 × 10-10 m). The calculated enthalpy, entropy, Gibbs energy, and equilibrium constant of HMB-TCNE complex formation in gas phase are: DeltaH0 = -61.59 kJ mol-1, DeltaSc0 = -143 J mol-1 K-1, DeltaG0 = -18.97 kJ mol-1, and K = 2,100 dm3 mol-1. Experimental data, however, measured in CCl4 are significantly lower: DeltaH0 = -34 kJ mol-1, DeltaSc0 = -70.4 J mol-1 K-1, DeltaG0 = -13.01 kJ mol-1, and K = 190 dm3 mol-1. The differences are caused by solvation effects which stabilize more the isolated components than the complex. The total solvent destabilization of Gibbs energy of the complex relatively to that of components is equal to 5.9 kJ mol-1 which is very close to our PCM value 6.5 kJ mol-1. MP2/6-31G* dipole moment and polarizabilities are in reasonable agreement with experiment (3.56 D versus 2.8 D for dipole moment). The difference here is due to solvent effect which enlarges interplanar distance and thus decreases dipole moment value. The MP2/6-31G* study supplemented by DFT-D parameterization for enthalpy calculation, and by the PCM approach to include solvent effect seems to be proper tools to elucidate the properties of pi

One-dimensional mercury(II) halide coordination polymers of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine ligand: Synthesis, crystal structure, spectroscopic and DFT studies

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

Saghatforoush, Lotfali, E-mail: saghatforoush@gmail.com; Khoshtarkib, Zeinab; Amani, Vahid

2016-01-15

Three new coordination polymers, [Hg(μ-bptz)X{sub 2}]{sub n} (X=Cl (1), Br (2)) and [Hg{sub 2}(μ-bptz)(μ-I){sub 2}I{sub 2}]{sub n} (3) (bptz=3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) were synthesized. X-ray structural analysis indicated that compounds 1 and 2 are composed of one-dimensional (1D) linear chains while the compound 3 has 1D stair-stepped structure. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that compound 1 and 2 are direct band gap semiconductors; however, compound 3 is an indirect semiconductor. The linear optical properties of the compounds are also calculated by DFT method. According to the DFT calculations, the observed emission bandmore » of the compounds in solid state is due to electron transfer from an excited bptz-π* state (CBs) to the top of VBs. {sup 1}H NMR spectra of the compounds indicate that, in solution phase, the compounds don’t decompose completely. Thermal stability of the compounds is studied using TG, DTA methods. - Graphical abstract: Synthesis, crystal structure and emission spectra of [Hg(μ-bptz)X{sub 2}]{sub n} (X=Cl and Br) and [Hg{sub 2}(μ-bptz)(μ-I){sub 2}I{sub 2}]{sub n} are presented. The electronic band structure and linear optical properties of the compounds are calculated by the DFT method. - Highlights: • Three 1D Hg(II) halide coordination polymers with bptz ligand have been prepared. • The structures of the compounds are determined by single crystal XRD. • DFT calculations show that [Hg(μ-bptz)X{sub 2}]{sub n} (X=Cl and Br) have a direct band gap. • DFT calculations show that [Hg{sub 2}(μ-bptz)(μ-I){sub 2}I{sub 2}]{sub n} has an indirect band gap. • The compounds show an intraligand electron transfer emission band in solid state.« less

Antimicrobial activities, DNA interactions, spectroscopic (FT-IR and UV-Vis) characterizations, and DFT calculations for pyridine-2-carboxylic acid and its derivates

NASA Astrophysics Data System (ADS)

Tamer, Ömer; Tamer, Sevil Arabacı; İdil, Önder; Avcı, Davut; Vural, Hatice; Atalay, Yusuf

2018-01-01

In this paper, pyridine- 2- carboxylic acid, also known as picolinic acid (pic), and its two derivate, 4- methoxy-pyridine- 2- carboxylic acid (4-Mpic) and 4- chloro-pyridine- 2- carboxylic acid (4-Clpic) have been characterized by FT-IR and UV-Vis spectroscopy techniques as well as DFT calculations. B3LYP level of Density Functional Theory (DFT) method was used to obtain ground state geometries, vibration wavenumbers, first order hyperpolarizabilities and molecular electrostatic potential (MEP) surfaces for pic, 4Clpic and 4Mpic. The electronic absorption wavelengths and HOMO-LUMO energies were investigated by time dependent B3LYP (TD-B3LYP) level with the conductor-like polarizable continuum model (CPCM). The effects of Cl atom and OCH3 group on HOMO-LUMO energy gaps and first order hyperpolarizability parameters of pic, 4Clpic and 4Mpic molecules were examined. All molecules were screened for their antibacterial activities against Gram-positive and Gram-negative bacteria and for their antifungal activities against yeast strains by using minimal inhibitory concentration method (MIC). All compounds (pic, 4Mpic and 4Clpic) have been found to be very active against to the Gram (+) and Gram (-) bacteria. The DNA interactions of pic, 4Clpic and 4Mpic were analyzed by molecular docking simulations, and the interaction of the 4Mpic molecule with DNA is found to be higher than 4Clpic and pic.

Doped phosphorene for hydrogen capture: A DFT study

NASA Astrophysics Data System (ADS)

Zhang, Hong-ping; Hu, Wei; Du, Aijun; Lu, Xiong; Zhang, Ya-ping; Zhou, Jian; Lin, Xiaoyan; Tang, Youhong

2018-03-01

Hydrogen capture and storage is the core of hydrogen energy application. With its high specific surface area, direct bandgap, and variety of potential applications, phosphorene has attracted much research interest. In this study, density functional theory (DFT) is utilized to study the interactions between doped phosphorenes and hydrogen molecules. The effects of different dopants and metallic or nonmetallic atoms on phosphorene/hydrogen interactions is systematically studied by adsorption energy, electron density difference, partial density of states analysis, and Hirshfeld population. Our results indicate that the metallic dopants Pt, Co, and Ni can help to improve the hydrogen capture ability of phosphorene, whereas the nonmetallic dopants have no effect on it. Among the various metallic dopants, Pt performs very differently, such that it can help to dissociate H2 on phosphorene. Specified doped phosphorene could be a promising candidate for hydrogen storage, with behaviors superior to those of intrinsic graphene sheet.

77 FR 66463 - Change in Bank Control Notices; Acquisitions of Shares of a Bank or Bank Holding Company

Federal Register 2010, 2011, 2012, 2013, 2014

2012-11-05

... 63166-2034: 1. R. Forest Taylor and Zora Taylor, both of Morgantown, Kentucky, as the largest individual..., Tennessee; Emily Ann Romans, Russellville, Kentucky; Robert Daniel Taylor, and Sharon Kay Taylor, both of...

DFT simulations of water adsorption and activation on low-index α-Ga2O3 surfaces.

PubMed

Zhou, Xin; Hensen, Emiel J M; van Santen, Rutger A; Li, Can

2014-06-02

Density functional theory (DFT) calculations are used to explore water adsorption and activation on different α-Ga2O3 surfaces, namely (001), (100), (110), and (012). The geometries and binding energies of molecular and dissociative adsorption are studied as a function of coverage. The simulations reveal that dissociative water adsorption on all the studied low-index surfaces are thermodynamically favorable. Analysis of surface energies suggests that the most preferentially exposed surface is (012). The contribution of surface relaxation to the respective surface energies is significant. Calculations of electron local density of states indicate that the electron-energy band gaps for the four investigated surfaces appears to be less related to the difference in coordinative unsaturation of the surface atoms, but rather to changes in the ionicity of the surface chemical bonds. The electrochemical computation is used to investigate the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on α-Ga2O3 surfaces. Our results indicate that the (100) and (110) surfaces, which have low stability, are the most favorable ones for HER and OER, respectively. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

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.

DFT calculation of pKa’s for dimethoxypyrimidinylsalicylic based herbicides

NASA Astrophysics Data System (ADS)

Delgado, Eduardo J.

2009-03-01

Dimethoxypyrimidinylsalicylic derived compounds show potent herbicidal activity as a result of the inhibition of acetohydroxyacid synthase, the first common enzyme in the biosynthetic pathway of the branched-chain aminoacids (valine, leucine and isoleucine) in plants, bacteria and fungi. Despite its practical importance, this family of compounds have been poorly characterized from a physico-chemical point of view. Thus for instance, their pK a's have not been reported earlier neither experimentally nor theoretically. In this study, the acid-dissociation constants of 39 dimethoxypyrimidinylsalicylic derived herbicides are calculated by DFT methods at B3LYP/6-31G(d,p) level of theory. The calculated values are validated by two checking tests based on the Hammett equation.

Spin-Forbidden Reactions: Adiabatic Transition States Using Spin-Orbit Coupled Density Functional Theory.

PubMed

Gaggioli, Carlo Alberto; Belpassi, Leonardo; Tarantelli, Francesco; Harvey, Jeremy N; Belanzoni, Paola

2018-04-06

A spin-forbidden chemical reaction involves a change in the total electronic spin state from reactants to products. The mechanistic study is challenging because such a reaction does not occur on a single diabatic potential energy surface (PES), but rather on two (or multiple) spin diabatic PESs. One possible approach is to calculate the so-called "minimum energy crossing point" (MECP) between the diabatic PESs, which however is not a stationary point. Inclusion of spin-orbit coupling between spin states (SOC approach) allows the reaction to occur on a single adiabatic PES, in which a transition state (TS SOC) as well as activation free energy can be calculated. This Concept article summarizes a previously published application in which, for the first time, the SOC effects, using spin-orbit ZORA Hamiltonian within density functional theory (DFT) framework, are included and account for the mechanism of a spin-forbidden reaction in gold chemistry. The merits of the MECP and TS SOC approaches and the accuracy of the results are compared, considering both our recent calculations on molecular oxygen addition to gold(I)-hydride complexes and new calculations for the prototype spin-forbidden N 2 O and N 2 Se dissociation reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

DFT molecular modeling and NMR conformational analysis of a new longipinenetriolone diester

NASA Astrophysics Data System (ADS)

Cerda-García-Rojas, Carlos M.; Guerra-Ramírez, Diana; Román-Marín, Luisa U.; Hernández-Hernández, Juan D.; Joseph-Nathan, Pedro

2006-05-01

The structure and conformational behavior of the new natural compound (4 R,5 S,7 S,8 R,9 S,10 R,11 R)-longipin-2-en-7,8,9-triol-1-one 7-angelate-9-isovalerate (1) isolated from Stevia eupatoria, were studied by molecular modeling and NMR spectroscopy. A Monte Carlo search followed by DFT calculations at the B3LYP/6-31G* level provided the theoretical conformations of the sesquiterpene framework, which were in full agreement with results derived from the 1H- 1H coupling constant analysis.

DFT investigations of the hydrogenation effect on silicene/graphene hybrids.

PubMed

Drissi, L B; Saidi, E H; Bousmina, M; Fassi-Fehri, O

2012-12-05

We report here a study on the effect of hydrogenation on a new one-atom thick material made of silicon and carbon atoms (silicene/graphene (SG) hybrid) within density functional theory. The structural, electronic and magnetic properties are investigated for non-, semi- and fully hydrogenated SG hybrids in a chair configuration and are compared with their parent materials. Calculations reveal that pure SG is a non-zero band gap semi-conductor with stable planar honeycomb structure. So mixing C and Si in an alternating manner gives another way to generate a finite band gap in one-atom thick materials. Fully hydrogenation makes the gap larger; however half chemical modification with H reduces the gap in favor of ferromagnetism order. The findings of this work open a wide spectrum of possibilities for designing SG-based nanodevices with controlled and tuned properties.

Lipophilicity Assessment of Ruthenium(II)-Arene Complexes by the Means of Reversed-Phase Thin-Layer Chromatography and DFT Calculations

PubMed Central

Shweshein, Khalil Salem A. M.; Andrić, Filip; Radoičić, Aleksandra; Gruden-Pavlović, Maja; Tešić, Živoslav; Milojković-Opsenica, Dušanka

2014-01-01

The lipophilicity of ten ruthenium(II)-arene complexes was assessed by reversed-phase thin-layer chromatography (RP-TLC) on octadecyl silica stationary phase. The binary solvent systems composed of water and acetonitrile were used as mobile phase in order to determine chromatographic descriptors for lipophilicity estimation. Octanol-water partition coefficient, logK OW, of tested complexes was experimentally determined using twenty-eight standard solutes which were analyzed under the same chromatographic conditions as target substances. In addition, ab initio density functional theory (DFT) computational approach was employed to calculate logK OW values from the differences in Gibbs' free solvation energies of the solute transfer from n-octanol to water. A good overall agreement between DFT calculated and experimentally determined logK OW values was established (R 2 = 0.8024–0.9658). PMID:24587761

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.

Development of Xe and Kr empirical potentials for CeO 2, ThO 2, UO 2 and PuO 2, combining DFT with high temperature MD

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

Cooper, M. W. D.; Kuganathan, N.; Burr, P. A.

In this study, the development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO 2, ThO 2, UO 2 and PuO 2. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matchingmore » to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO 2, ThO 2, UO 2 and PuO 2, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO 2 as well as advanced MOX fuels.« less

Development of Xe and Kr empirical potentials for CeO 2, ThO 2, UO 2 and PuO 2, combining DFT with high temperature MD

DOE PAGES

Cooper, M. W. D.; Kuganathan, N.; Burr, P. A.; ...

2016-08-23

In this study, the development of embedded atom method (EAM) many-body potentials for actinide oxides and associated mixed oxide (MOX) systems has motivated the development of a complementary parameter set for gas-actinide and gas-oxygen interactions. A comprehensive set of density functional theory (DFT) calculations were used to study Xe and Kr incorporation at a number of sites in CeO 2, ThO 2, UO 2 and PuO 2. These structures were used to fit a potential, which was used to generate molecular dynamics (MD) configurations incorporating Xe and Kr at 300 K, 1500 K, 3000 K and 5000 K. Subsequent matchingmore » to the forces predicted by DFT for these MD configurations was used to refine the potential set. This fitting approach ensured weighted fitting to configurations that are thermodynamically significant over a broad temperature range, while avoiding computationally expensive DFT-MD calculations. The resultant gas potentials were validated against DFT trapping energies and are suitable for simulating combinations of Xe and Kr in solid solutions of CeO 2, ThO 2, UO 2 and PuO 2, providing a powerful tool for the atomistic simulation of conventional nuclear reactor fuel UO 2 as well as advanced MOX fuels.« less

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.

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

Relaxations of fluorouracil tautomers by decorations of fullerene-like SiCs: DFT studies

NASA Astrophysics Data System (ADS)

Kouchaki, Alireza; Gülseren, Oğuz; Hadipour, Nasser; Mirzaei, Mahmoud

2016-06-01

Decorations of silicon carbide (SiC) fullerene-like nanoparticles by fluorouracil (FU) and its tautomers are investigated through density functional theory (DFT) calculations. Two models of fullerene-like particles including Si12C8 and Si8C12 are constructed to be counterparts of decorated hybrid structures, FU@Si12C8 and FU@Si8C12, respectively. The initial models including original FU and tautomeric structures and SiC nanoparticles are individually optimized and then combined for further optimizations in the hybrid forms. Covalent bonds are observed for FU@Si12C8 hybrids, whereas non-covalent interactions are seen for FU@Si8C12 ones. The obtained properties indicated that Si12C8 model could be considered as a better counterpart for interactions with FU structures than Si8C12 model. The results also showed significant effects of interactions on the properties of atoms close to the interacting regions in nanoparticles. Finally, the tautomeric structures show different behaviors in interactions with SiC nanoparticles, in which the SiC nanoparticles could be employed to detect the situations of tautomeric processes for FU structures.

DFT calculation and vibrational spectroscopic studies of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine

NASA Astrophysics Data System (ADS)

Premkumar, S.; Jawahar, A.; Mathavan, T.; Kumara Dhas, M.; Sathe, V. G.; Milton Franklin Benial, A.

2014-08-01

The molecular structure of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine (BABP) was optimized by the DFT/B3LYP method with 6-311G (d,p), 6-311++G (d,p) and cc-pVTZ basis sets using the Gaussian 09 program. The most stable optimized structure of the molecule was predicted by the DFT/B3LYP method with cc-pVTZ basis set. The vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals and thermodynamical parameters were calculated. These calculations were done at the ground state energy level of BABP without applying any constraint on the potential energy surface. The vibrational spectra were experimentally recorded using Fourier Transform-Infrared (FT-IR) and micro-Raman spectrometer. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies. The complete theoretically calculated and experimentally observed vibrational frequencies were assigned on the basis of Potential Energy Distribution (PED) calculation using the VEDA 4.0 program. The vibrational modes assignments were performed by using the animation option of GaussView 05 graphical interface for Gaussian program. The Mulliken atomic charge distribution was calculated for BABP molecule. The molecular reactivity and stability of BABP were also studied by frontier molecular orbitals (FMOs) analysis.

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.

DFTBaby: A software package for non-adiabatic molecular dynamics simulations based on long-range corrected tight-binding TD-DFT(B)

NASA Astrophysics Data System (ADS)

Humeniuk, Alexander; Mitrić, Roland

2017-12-01

A software package, called DFTBaby, is published, which provides the electronic structure needed for running non-adiabatic molecular dynamics simulations at the level of tight-binding DFT. A long-range correction is incorporated to avoid spurious charge transfer states. Excited state energies, their analytic gradients and scalar non-adiabatic couplings are computed using tight-binding TD-DFT. These quantities are fed into a molecular dynamics code, which integrates Newton's equations of motion for the nuclei together with the electronic Schrödinger equation. Non-adiabatic effects are included by surface hopping. As an example, the program is applied to the optimization of excited states and non-adiabatic dynamics of polyfluorene. The python and Fortran source code is available at http://www.dftbaby.chemie.uni-wuerzburg.de.

Cd hyperfine interactions in DNA bases and DNA of mouse strains infected with Trypanosoma cruzi investigated by perturbed angular correlation spectroscopy and ab initio calculations.

PubMed

Petersen, Philippe A D; Silva, Andreia S; Gonçalves, Marcos B; Lapolli, André L; Ferreira, Ana Maria C; Carbonari, Artur W; Petrilli, Helena M

2014-06-03

In this work, perturbed angular correlation (PAC) spectroscopy is used to study differences in the nuclear quadrupole interactions of Cd probes in DNA molecules of mice infected with the Y-strain of Trypanosoma cruzi. The possibility of investigating the local genetic alterations in DNA, which occur along generations of mice infected with T. cruzi, using hyperfine interactions obtained from PAC measurements and density functional theory (DFT) calculations in DNA bases is discussed. A comparison of DFT calculations with PAC measurements could determine the type of Cd coordination in the studied molecules. To the best of our knowledge, this is the first attempt to use DFT calculations and PAC measurements to investigate the local environment of Cd ions bound to DNA bases in mice infected with Chagas disease. The obtained results also allowed the detection of local changes occurring in the DNA molecules of different generations of mice infected with T. cruzi, opening the possibility of using this technique as a complementary tool in the characterization of complicated biological systems.

Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions. A Combined EPR and DFT Study

DOE PAGES

Mardis, Kristy L.; Webb, J.; Holloway, Tarita; ...

2015-12-03

Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advancedmore » electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM.« less

PyGlobal: A toolkit for automated compilation of DFT-based descriptors.

PubMed

Nath, Shilpa R; Kurup, Sudheer S; Joshi, Kaustubh A

2016-06-15

Density Functional Theory (DFT)-based Global reactivity descriptor calculations have emerged as powerful tools for studying the reactivity, selectivity, and stability of chemical and biological systems. A Python-based module, PyGlobal has been developed for systematically parsing a typical Gaussian outfile and extracting the relevant energies of the HOMO and LUMO. Corresponding global reactivity descriptors are further calculated and the data is saved into a spreadsheet compatible with applications like Microsoft Excel and LibreOffice. The efficiency of the module has been accounted by measuring the time interval for randomly selected Gaussian outfiles for 1000 molecules. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Armchair and zigzag nanoribbons of gold and silver: A DFT study

NASA Astrophysics Data System (ADS)

Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

2018-04-01

This paper presents the results from a DFT-based computational study of structural and electronic properties of zigzag and armchair edge shaped nanoribbons of gold and silver in hexagonal phase. The cohesive energy of the considered nanoribbons are found to be more than the corresponding 2D counterpart, thereby, suggesting Au and Ag nanoribbons to be more stable in 1D as compared to 2D. All nanoribbons are found to be metallic with a modulation in quantum ballistic conductance with length and edge type of the nanoribbon. Au nanoribbons are found to have higher conductance than Ag nanoribbon. There is increase in conductance with increase in length of nanoribbon.

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.

Enhancement of DFT-calculations at petascale: Nuclear Magnetic Resonance, Hybrid Density Functional Theory and Car-Parrinello calculations

NASA Astrophysics Data System (ADS)

Varini, Nicola; Ceresoli, Davide; Martin-Samos, Layla; Girotto, Ivan; Cavazzoni, Carlo

2013-08-01

One of the most promising techniques used for studying the electronic properties of materials is based on Density Functional Theory (DFT) approach and its extensions. DFT has been widely applied in traditional solid state physics problems where periodicity and symmetry play a crucial role in reducing the computational workload. With growing compute power capability and the development of improved DFT methods, the range of potential applications is now including other scientific areas such as Chemistry and Biology. However, cross disciplinary combinations of traditional Solid-State Physics, Chemistry and Biology drastically improve the system complexity while reducing the degree of periodicity and symmetry. Large simulation cells containing of hundreds or even thousands of atoms are needed to model these kind of physical systems. The treatment of those systems still remains a computational challenge even with modern supercomputers. In this paper we describe our work to improve the scalability of Quantum ESPRESSO (Giannozzi et al., 2009 [3]) for treating very large cells and huge numbers of electrons. To this end we have introduced an extra level of parallelism, over electronic bands, in three kernels for solving computationally expensive problems: the Sternheimer equation solver (Nuclear Magnetic Resonance, package QE-GIPAW), the Fock operator builder (electronic ground-state, package PWscf) and most of the Car-Parrinello routines (Car-Parrinello dynamics, package CP). Final benchmarks show our success in computing the Nuclear Magnetic Response (NMR) chemical shift of a large biological assembly, the electronic structure of defected amorphous silica with hybrid exchange-correlation functionals and the equilibrium atomic structure of height Porphyrins anchored to a Carbon Nanotube, on many thousands of CPU cores.

A DFT study of the mechanism and the regioselectivity of [3 + 2] cycloaddition reactions of nitrile oxides with α,β-acetylenic aldehyde

NASA Astrophysics Data System (ADS)

Sobhi, Chafia; Nacereddine, Abdelmalek Khorief; Nasri, Lilia; Lechtar, Zohra; Djerourou, Abdelhafid

2016-11-01

A DFT study of the (32CA) reaction of a series of some nitrile oxides with electron-deficient alkyne (3-phenylpropionlaldehyde) in gas phase and in toluene has been carried out using B3LYP functional with 6-31G(d) basis set. Two reactive channels 4- and 5-associated with the two regioisomeric modes have been located and characterised. These 32CA reactions are characterised by a low asynchronous one-step mechanism with a low-polar character. Analysis of the DFT reactivity indices indicates that the nucleophilic centre of the different nitrile oxides accounts for the 4-regioselectivity. Our calculations are in a good agreement with the experimental findings.

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.

Water adsorption in SAPO-34: elucidating the role of local heterogeneities and defects using dispersion-corrected DFT calculations.

PubMed

Fischer, Michael

2015-10-14

The chabazite-type silicoaluminophosphate SAPO-34 is a promising adsorbent for applications in thermal energy storage using water adsorption-desorption cycles. In order to develop a microscopic understanding of the impact of local heterogeneities and defects on the water adsorption properties, the interaction of different models of SAPO-34 with water was studied using dispersion-corrected density-functional theory (DFT-D) calculations. In addition to SAPO-34 with isolated silicon atoms, the calculations considered models incorporating two types of heterogeneities (silicon islands, aluminosilicate domains), and two defect-containing (partially and fully desilicated) systems. DFT-D optimisations were performed for systems with small amounts of adsorbed water, in which all H2O molecules can interact with framework protons, and systems with large amounts of adsorbed water (30 H2O molecules per unit cell). At low loadings, the host-guest interaction energy calculated for SAPO-34 with isolated Si atoms amounts to approximately -90 kJ mol(-1). While the presence of local heterogeneities leads to the creation of some adsorption sites that are energetically slightly more favourable, the interaction strength is drastically reduced in systems with defects. At high water loadings, energies in the range of -70 kJ mol(-1) are obtained for all models. The DFT-D interaction energies are in good agreement with experimentally measured heats of water adsorption. A detailed analysis of the equilibrium structures was used to gain insights into the binding modes at low coverages, and to assess the extent of framework deprotonation and changes in the coordination environment of aluminium atoms at high water loadings.

A RRKM study and a DFT assessment on gas-phase fragmentation of formamide-M(2+) (M = Ca, Sr).

PubMed

Martín-Sómer, Ana; Gaigeot, Marie-Pierre; Yáñez, Manuel; Spezia, Riccardo

2014-07-28

A kinetic study of the unimolecular reactivity of formamide-M(2+) (M = Ca, Sr) systems was carried out by means of RRKM statistical theory using high-level DFT. The results predict M(2+), [M(NH2)](+) and [HCO](+) as the main products, together with an intermediate that could eventually evolve to produce [M(NH3)](2+) and CO, for high values of internal energy. In this framework, we also evaluated the influence of the external rotational energy on the reaction rate constants. In order to find a method to perform reliable electronic structure calculations for formamide-M(2+) (M = Ca, Sr) at a relatively low computational cost, an assessment of different methods was performed. In the first assessment twenty-one functionals, belonging to different DFT categories, and an MP2 wave function method using a small basis set were evaluated. CCSD(T)/cc-pWCVTZ single point calculations were used as reference. A second assessment has been performed on geometries and energies. We found BLYP/6-31G(d) and G96LYP/6-31+G(d,p) as the best performing methods, for formamide-Ca(2+) and formamide-Sr(2+), respectively. Furthermore, a detailed assessment was done on RRKM reactivity and G96LYP/6-31G(d) provided results in agreement with higher level calculations. The combination of geometrical, energetics and kinetics (RRKM) criteria to evaluate DFT functionals is rather unusual and provides an original assessment procedure. Overall, we suggest using G96LYP as the best performing functional with a small basis set for both systems.

Crystallographic structure refinement with quadrupolar nuclei: a combined solid-state NMR and GIPAW DFT example using MgBr(2).

PubMed

Widdifield, Cory M; Bryce, David L

2009-09-07

Solid-state NMR spectroscopy and GIPAW DFT calculations reveal the pronounced sensitivity of (79/81)Br and (25)Mg quadrupolar coupling constants to subtle aspects of solid state structure which were not previously detected by pXRD methods.

Behaviour of DFT-based approaches to the spin-orbit term of zero-field splitting tensors: a case study of metallocomplexes, MIII(acac)3 (M = V, Cr, Mn, Fe and Mo).

PubMed

Sugisaki, Kenji; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji

2017-11-15

Spin-orbit contributions to the zero-field splitting (ZFS) tensor (D SO tensor) of M III (acac) 3 complexes (M = V, Cr, Mn, Fe and Mo; acac = acetylacetonate anion) are evaluated by means of ab initio (a hybrid CASSCF/MRMP2) and DFT (Pederson-Khanna (PK) and natural orbital-based Pederson-Khanna (NOB-PK)) methods, focusing on the behaviour of DFT-based approaches to the D SO tensors against the valence d-electron configurations of the transition metal ions in octahedral coordination. Both the DFT-based approaches reproduce trends in the D tensors. Significantly, the differences between the theoretical and experimental D (D = D ZZ - (D XX + D YY )/2) values are smaller in NOB-PK than in PK, emphasising the usefulness of the natural orbital-based approach to the D tensor calculations of transition metal ion complexes. In the case of d 2 and d 4 electronic configurations, the D SO (NOB-PK) values are considerably underestimated in the absolute magnitude, compared with the experimental ones. The D SO tensor analysis based on the orbital region partitioning technique (ORPT) revealed that the D SO contributions attributed to excitations from the singly occupied region (SOR) to the unoccupied region (UOR) are significantly underestimated in the DFT-based approaches to all the complexes under study. In the case of d 3 and d 5 configurations, the (SOR → UOR) excitations contribute in a nearly isotropic manner, which causes fortuitous error cancellations in the DFT-based D SO values. These results indicate that more efforts to develop DFT frameworks should be directed towards the reproduction of quantitative D SO tensors of transition metal complexes with various electronic configurations and local symmetries around metal ions.

Pd (II) complexes of bidentate chalcone ligands: Synthesis, spectral, thermal, antitumor, antioxidant, antimicrobial, DFT and SAR studies

NASA Astrophysics Data System (ADS)

Gaber, Mohamed; Awad, Mohamed K.; Atlam, Faten M.

2018-05-01

The ligation behavior of two chalcone ligands namely, (E)-3-(4-chlorophenyl)-1-(pyridin-2-yl)prop-2-en-1-one (L1) and (E)-3-(4-methoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one (L2), towards the Pd(II) ion is determined. The structures of the complexes are elucidated by elemental analysis, spectral methods (IR, electronic and NMR spectra) as well as the conductance measurements and thermal analysis. The metal complexes exhibit a square planar geometrical arrangement. The kinetic and thermodynamic parameters for some selected decomposition steps have been calculated. The antimicrobial, antioxidant and anticancer activities of the chalcones and their Pd(II) complexes have been evaluated. Molecular orbital computations are performed using DFT at B3LYP level with 6-31 + G(d) and LANL2DZ basis sets to access reliable results to the experimental values. The calculations are performed to obtain the optimized molecular geometry, charge density distribution, extent of distortion from regular geometry. Thermodynamic parameters for the investigated compounds are also studied. The calculations confirm that the investigated complexes have square planner geometry, which is in a good agreement with the experimental observation.

A DFT study for the structural and electronic properties of Zn m Se n nanoclusters

NASA Astrophysics Data System (ADS)

Yadav, Phool Singh; Pandey, Dheeraj Kumar

2012-09-01

An ab initio study has been performed for the stability, structural and electronic properties of 19 small zinc selenide Zn m Se n ( m + n = 2-4) nanoclusters. Out of these nanoclusters, one nanocluster is found to be unstable due to its imaginary vibrational frequency. A B3LYP-DFT/6-311G(3df) method is used in the optimization of the geometries of the nanoclusters. We have calculated the zero point energy (ZPE), which is ignored by the other workers. The binding energies (BE), HOMO-LUMO gaps and bond lengths have been obtained for all the optimized nanoclusters. For the same value of ` m' and ` n', we designate the most stable structure the one, which has maximum final binding energy (FBE) per atom. The adiabatic and vertical ionization potentials (IP) and electron affinities (EA), dipole moments and charge on atoms have been investigated for the most stable nanoclusters. For the same value of ` m' and ` n', the nanocluster containing maximum number of Se atoms is found to be most stable.

Multicomponent DFT study of geometrical H/D isotope effect on hydrogen-bonded organic conductor, κ-H3(Cat EDT-ST)2

NASA Astrophysics Data System (ADS)

Yamamoto, Kaichi; Kanematsu, Yusuke; Nagashima, Umpei; Ueda, Akira; Mori, Hatsumi; Tachikawa, Masanori

2017-04-01

We theoretically investigated a significant contraction of the hydrogen-bonding O⋯O distance upon H/D substitution in our recently developed purely organic crystals, κ-H3(Cat-EDT-ST)2 (H-ST) and its isotopologue κ-D3(Cat-EDT-ST)2 (D-ST), having π-electron systems coupled with hydrogen-bonding fluctuation. The origin of this geometrical H/D isotope effect was elucidated by using the multicomponent DFT method, which takes the H/D nuclear quantum effect into account. The optimized O⋯O distance in H-ST was found to be longer than that in D-ST due to the anharmonicity of the potential energy curve along the Osbnd H bond direction, which was in reasonable agreement with the experimental trend.

DFT Study on the Complexation of Bambus[6]uril with the Perchlorate and Tetrafluoroborate Anions.

PubMed

Toman, Petr; Makrlík, Emanuel; Vaňura, Petr

2011-12-01

By using quantum mechanical DFT calculations, the most probable structures of the bambus[6]uril.ClO4- and bambus[6]uril.BF4- anionic complex species were derived. In these two complexes having C3 symmetry, each of the considered anions, included in the macrocyclic cavity, is bound by 12 weak hydrogen bonds between methine hydrogen atoms on the convex face of glycoluril units and the respective anion.

A new look into the quantum chemical and spectroscopic investigations of 5-chloro-1-methyl-4-nitroimidazole.

PubMed

Arjunan, V; Raj, Arushma; Anitha, R; Mohan, S

2014-05-05

Optimised geometrical structural parameters, harmonic vibrational frequencies, natural bonding orbital analysis and frontier molecular orbitals are determined by B3LYP and B3PW91 methods. The exact geometry of 5-chloro-1-methyl-4-nitroimidazole is determined through conformational analysis. The experimentally observed infrared and Raman bands have been assigned and analysed. The (13)C and (1)H NMR chemical shifts of the compound are investigated. The total electron density and molecular electrostatic potentials are determined. The electrostatic potential (electron+nuclei) distribution, molecular shape, size and dipole moments of the molecule have been displayed. The energies of the frontier molecular orbitals and LUMO-HOMO energy gap are measured. The possible electronic transitions of the molecule are studied by TD-DFT method along with the UV-Visible spectrum. The structure-activity relationship of the compound is also investigated by conceptual DFT methods. Copyright © 2014 Elsevier B.V. All rights reserved.

Ag nanoparticle decorated molybdenum oxide structures: growth, characterization, DFT studies and their application to enhanced field emission

NASA Astrophysics Data System (ADS)

Guha, Puspendu; Ghosh, Arnab; Thapa, Ranjit; Mathan Kumar, E.; Kirishwaran, Sabari; Singh, Ranveer; Satyam, Parlapalli V.

2017-10-01

We report a simple single step growth of α-MoO3 structures and energetically suitable site specific Ag nanoparticle (NP) decorated α-MoO3 structures on varied substrates, having almost similar morphologies and oxygen vacancies. We elucidate possible growth mechanisms in light of experimental findings and density functional theory (DFT) calculations. We experimentally establish and verified by DFT calculations that the MoO3(010) surface is a weakly interacting and stable surface compared to other orientations. From DFT study, the binding energy is found to be higher for (100) and (001) surfaces (˜-0.98 eV), compared to the (010) surface (˜-0.15 eV) and thus it is likely that Ag NP formation is not favorable on the MoO3(010) surface. The Ag decorated MoO3 (Ag-MoO3) nanostructured sample shows enhanced field emission properties with an approimately 2.1 times lower turn-on voltage of 1.67 V μm-1 and one order higher field enhancement factor (β) of 8.6 × 104 compared to the MoO3 sample without Ag incorporation. From Kelvin probe force microscopy measurements, the average local work function (Φ) is found to be approximately 0.47 eV smaller for the Ag-MoO3 sample (˜5.70 ± 0.05 eV) compared to the MoO3 sample (˜6.17 ± 0.05 eV) and the reduction in Φ can be attributed to the shifting Fermi level of MoO3 toward vacuum via electron injection from Ag NPs to MoO3. The presence of oxygen vacancies together with Ag NPs lead to the highest β and lowest turn-on field among the reported values under the MoO3 emitter category.

Synthesis, spectroscopic characterizations, crystal structures and DFT studies of nalidixic acid carbonyl hydrazones derivatives

NASA Astrophysics Data System (ADS)

Bergamini, F. R. G.; Ribeiro, M. A.; Lancellotti, M.; Machado, D.; Miranda, P. C. M. L.; Cuin, A.; Formiga, A. L. B.; Corbi, P. P.

2016-09-01

This article describes the synthesis and characterization of the 1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carbohydrazide (hzd) and six carbonyl hydrazones derivatives of the nalidixic with 1H-pyrrol-2-ylmethylidene (hpyrr), 1H-imidazol-2-ylmethylidene (h2imi), pyridin-2-ylmethylidene (h2py), pyridin-3-ylmethylidene (h3py), pyridin-4-ylmethylidene(h4py) and (2-hydroxyphenyl)methylidene (hsali). The carbonyl hydrazones were characterized by elemental and ESI-QTOF-MS analyses, IR and detailed NMR spectroscopic measurements. The 2D NMR experiments allowed the unambiguous assignment of the hydrogen, carbon and nitrogen atoms, which have not been reported for nalidixic acid carbonyl hydrazone derivatives so far. Crystal structures of hzd and the new carbonyl hydrazones h2imi, hpyrr and h3py were determined by X-ray diffraction studies. Although the synthesis of hzd was reported decades ago, the hzd crystal structure have not been reported yet. Geometric optimizations of all the characterized structures were performed with the aid of DFT studies. Despite the fact that the hydrazones with 2-pyridine carboxylic acid (h2py) and salicyl aldehyde (hsali) were already reported by literature, a detailed spectroscopic study followed by DFT studies are also reported for such compounds in this manuscript. Antimicrobial studies of the compounds are also presented.

DFT calculation and vibrational spectroscopic studies of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine.

PubMed

Premkumar, S; Jawahar, A; Mathavan, T; Kumara Dhas, M; Sathe, V G; Milton Franklin Benial, A

2014-08-14

The molecular structure of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine (BABP) was optimized by the DFT/B3LYP method with 6-311G (d,p), 6-311++G (d,p) and cc-pVTZ basis sets using the Gaussian 09 program. The most stable optimized structure of the molecule was predicted by the DFT/B3LYP method with cc-pVTZ basis set. The vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals and thermodynamical parameters were calculated. These calculations were done at the ground state energy level of BABP without applying any constraint on the potential energy surface. The vibrational spectra were experimentally recorded using Fourier Transform-Infrared (FT-IR) and micro-Raman spectrometer. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies. The complete theoretically calculated and experimentally observed vibrational frequencies were assigned on the basis of Potential Energy Distribution (PED) calculation using the VEDA 4.0 program. The vibrational modes assignments were performed by using the animation option of GaussView 05 graphical interface for Gaussian program. The Mulliken atomic charge distribution was calculated for BABP molecule. The molecular reactivity and stability of BABP were also studied by frontier molecular orbitals (FMOs) analysis. Copyright © 2014 Elsevier B.V. All rights reserved.

Evaluating DFT for Transition Metals and Binaries: Developing the V/DM-17 Test Set

NASA Astrophysics Data System (ADS)

Decolvenaere, Elizabeth; Mattsson, Ann

We have developed the V-DM/17 test set to evaluate the experimental accuracy of DFT calculations of transition metals. When simulation and experiment disagree, the disconnect in length-scales and temperatures makes determining ``who is right'' difficult. However, methods to evaluate the experimental accuracy of functionals in the context of solid-state materials science, especially for transition metals, is lacking. As DFT undergoes a shift from a descriptive to a predictive tool, these issues of verification are becoming increasingly important. With undertakings like the Materials Project leading the way in high-throughput predictions and discoveries, the development of a one-size-fits-most approach to verification is critical. Our test set evaluates 26 transition metal elements and 80 transition metal alloys across three physical observables: lattice constants, elastic coefficients, and formation energy of alloys. Whether or not the formation energy can be reproduced measures whether the relevant physics are captured in a calculation. This is especially important question in transition metals, where active d-electrons can thwart commonly used techniques. In testing the V/DM-17 test set, we offer new views into the performance of existing functionals. Sandia National Labs is a multi-mission laboratory managed and operated by Sandia Corp., a wholly owned subsidiary of Lockheed Martin Corp., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Combined UMC- DFT prediction of electron-hole coupling in unit cells of pentacene crystals.

PubMed

Leal, Luciano Almeida; de Souza Júnior, Rafael Timóteo; de Almeida Fonseca, Antonio Luciano; Ribeiro Junior, Luiz Antonio; Blawid, Stefan; da Silva Filho, Demetrio Antonio; da Cunha, Wiliam Ferreira

2017-05-01

Pentacene is an organic semiconductor that draws special attention from the scientific community due to the high mobility of its charge carriers. As electron-hole interactions are important aspects in the regard of such property, a computationally inexpensive method to predict the coupling between these quasi-particles is highly desired. In this work, we propose a hybrid methodology of combining Uncoupled Monte Carlo Simulations (UMC) and Density functional Theory (DFT) methodologies to obtain a good compromise between computational feasibility and accuracy. As a first step in considering a Pentacene crystal, we describe its unit cell: the Pentacene Dimer. Because many conformations can be encountered for the dimer and considering the complexity of the system, we make use of UMC in order to find the most probable structures and relative orientations for the Pentacene-Pentacene complex. Following, we carry out electronic structure calculations in the scope of DFT with the goal of describing the electron-hole coupling on the most probable configurations obtained by UMC. The comparison of our results with previously reported data on the literature suggests that the methodology is well suited for describing transfer integrals of organic semiconductors. The observed accuracy together with the smaller computational cost required by our approach allows us to conclude that such methodology might be an important tool towards the description of systems with higher complexity.

DFT study of the adsorption of 3-chloro-2-hydroxypropyl trimethylammonium chloride on montmorillonite surfaces in solution

NASA Astrophysics Data System (ADS)

Yang, Zongyi; Liu, Wenli; Zhang, He; Jiang, Xinli; Min, Fanfei

2018-04-01

The study of the adsorption mechanism of 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTA), which acts as an effective clay minerals hydration inhibitor, can provide an effective approach for the design of novel high-performance inhibitors with favorable molecular structures. Density functional theory (DFT) calculations were performed to investigate the adsorption mechanism of CHPTA on dry and hydrated montmorillonite (MMT) surfaces. The interactions between CHPTA, H2O, and MMT were systematically analyzed. It was found that CHPTA was mainly adsorbed on MMT by hydrogen bonds and especially electrostatic force and that the presence of Na ions favors the adsorption of CHPTA on the Na-(001) surface. In the presence of water molecules, the adsorption of CHPTA was promoted by H2O, which exhibited a cooperative adsorption effect by enhancing the MMT-CHPTA electrostatic force and by forming more hydrogen bonds and Hsbnd Cl bonds among CHPTA, H2O and MMT.

Experimental, DFT and molecular docking studies on 2-(2-mercaptophenylimino)-4-methyl-2H-chromen-7-ol

NASA Astrophysics Data System (ADS)

Singh, Ashok Kumar; Singh, Ravindra Kumar

2016-10-01

A new coumarin derivative 2-(2-mercaptophenylimino)-4-methyl-2H-chromen-7-ol (COMSB) was synthesized and characterized with the help of 1H,13C NMR, FT-IR, FT-Raman and mass spectrometry. All quantum calculations were performed at DFT level of theory using B3LYP functional and 6-31G (d,p) as basis set. The UV-Vis spectrum studied by TD-DFT theory, with a hybrid exchange-correlation functional using Coulomb-attenuating method (CAM-B3LYP) in solvent phase gives similar pattern of bands, at energies and is consistent with that of experimental findings. The detailed analysis of vibrational (IR and Raman) spectra and their assignments has been done by computing Potential Energy Distribution (PED) using Gar2ped. Intra-molecular interactions were analyzed by 'Atoms in molecule' (AIM) approach. Computed first static hyperpolarizability (β0 = 8.583 × 10-30 esu) indicates non-linear optical (NLO) response of the molecule. Molecular docking studies show that the title molecule may act as potential acetylcholine esterase (AChE) inhibitor.

Efficient DFT+U calculations of ballistic electron transport: Application to Au monatomic chains with a CO impurity

NASA Astrophysics Data System (ADS)

Sclauzero, Gabriele; Dal Corso, Andrea

2013-02-01

An efficient method for computing the Landauer-Büttiker conductance of an open quantum system within DFT+U is presented. The Hubbard potential is included in electronic-structure and transport calculations as a simple renormalization of the nonlocal pseudopotential coefficients by restricting the integration for the onsite occupations within the cutoff spheres of the pseudopotential. We apply the methodology to the case of an Au monatomic chain in the presence of a CO molecule adsorbed on it. We show that the Hubbard U correction removes the spurious magnetization in the pristine Au chain at the equilibrium spacing, as well as the unphysical contribution of d electrons to the conductance, resulting in a single (spin-degenerate) transmission channel and a more realistic conductance of 1G0. We find that the conductance reduction due to CO adsorption is much larger for the atop site than for the bridge site, so that the general picture of electron transport in stretched Au chains given by the local density approximation remains valid at the equilibrium Au-Au spacing within DFT+U.

Synthesis, spectroscopic studies, DFT calculations, electrochemical evaluation, BSA binding and molecular docking of an aroylhydrazone -based cis-dioxido Mo(VI) complex

NASA Astrophysics Data System (ADS)

Mohamadi, Maryam; Faghih-Mirzaei, Ehsan; Ebrahimipour, S. Yousef; Sheikhshoaie, Iran; Haase, Wolfgang; Foro, Sabine

2017-07-01

A cis-dioxido Mo(VI) complex, [MoO2(L)(MeOH)], [L2-: (3-methoxy-2-oxidobenzylidene) benzohydrazonate], has been synthesized and characterized using physicochemical and spectroscopic techniques including elemental analysis, FT-IR, 1HNMR, UV-Vis spectroscopy, molar conductivity and single crystal X-ray diffraction. DFT calculations in the ground state of the complex were carried out using hybrid functional B3LYP with DGDZVP as basis set. Non-linear optical properties including electric dipole moment (μ), polarizability (α) and molecular first hyperpolarizability (β) of the compound were also computed. The values of linear polarizability and first hyperpolarizability obtained for the studied molecule indicated that the compound could be a good candidate of nonlinear optical materials. TD-DFT calculation and molecular electrostatic potential (MEP) were also performed. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the complex at different temperatures have been calculated. The interaction of a synthesized complex, with bovine serum albumin was also thoroughly investigated using experimental and theoretical studies. UV-Vis absorption and fluorescence quenching techniques were used to determine the binding parameters as well as the mechanism of the interaction. The values of binding constants were in the range of 104-105 M-1 demonstrating a moderate interaction between the synthesized complex and BSA making the protein suitable for transportation and delivery of the compound. Thermodynamic parameters were also indicating a binding through van der Waals force or hydrogen bond of [MoO2(L)(MeOH)] to BSA. The results obtained from docking studies were consistent to those obtained from experimental studies.

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.

A general framework for numerical simulation of improvised explosive device (IED)-detection scenarios using density functional theory (DFT) and terahertz (THz) spectra.

PubMed

Shabaev, Andrew; Lambrakos, Samuel G; Bernstein, Noam; Jacobs, Verne L; Finkenstadt, Daniel

2011-04-01

We have developed a general framework for numerical simulation of various types of scenarios that can occur for the detection of improvised explosive devices (IEDs) through the use of excitation using incident electromagnetic waves. A central component model of this framework is an S-matrix representation of a multilayered composite material system. Each layer of the system is characterized by an average thickness and an effective electric permittivity function. The outputs of this component are the reflectivity and the transmissivity as functions of frequency and angle of the incident electromagnetic wave. The input of the component is a parameterized analytic-function representation of the electric permittivity as a function of frequency, which is provided by another component model of the framework. The permittivity function is constructed by fitting response spectra calculated using density functional theory (DFT) and parameter adjustment according to any additional information that may be available, e.g., experimentally measured spectra or theory-based assumptions concerning spectral features. A prototype simulation is described that considers response characteristics for THz excitation of the high explosive β-HMX. This prototype simulation includes a description of a procedure for calculating response spectra using DFT as input to the Smatrix model. For this purpose, the DFT software NRLMOL was adopted. © 2011 Society for Applied Spectroscopy

DFT-derived reactive potentials for the simulation of activated processes: the case of CdTe and CdTe:S.

PubMed

Hu, Xiao Liang; Ciaglia, Riccardo; Pietrucci, Fabio; Gallet, Grégoire A; Andreoni, Wanda

2014-06-19

We introduce a new ab initio derived reactive potential for the simulation of CdTe within density functional theory (DFT) and apply it to calculate both static and dynamical properties of a number of systems (bulk solid, defective structures, liquid, surfaces) at finite temperature. In particular, we also consider cases with low sulfur concentration (CdTe:S). The analysis of DFT and classical molecular dynamics (MD) simulations performed with the same protocol leads to stringent performance tests and to a detailed comparison of the two schemes. Metadynamics techniques are used to empower both Car-Parrinello and classical molecular dynamics for the simulation of activated processes. For the latter, we consider surface reconstruction and sulfur diffusion in the bulk. The same procedures are applied using previously proposed force fields for CdTe and CdTeS materials, thus allowing for a detailed comparison of the various schemes.

Synthesis, spectroscopic and DFT studies of novel 4-(morpholinomethyl)-5-oxo-1-phenylpyrrolidine-3-carboxylic acid

NASA Astrophysics Data System (ADS)

Devi, Poornima; Fatma, Shaheen; Bishnoi, Abha; Srivastava, Krishna; Shukla, Shraddha; Kumar, Roop

2018-04-01

A novel 4-(morpholinomethyl)-5-oxo-1-phenylpyrrolidine-3-carboxylic acid has been synthesized and its structural elucidation has been done by UV, FT-IR, 1H and 13C NMR spectroscopy. All quantum chemical calculations were carried out at level of density functional theory (DFT) with B3LYP function using 6-31G (d, p) basis atomic set. AIM approach has been incorporated for the analysis of various intermolecular interactions. Polarizability and hyperpolarizabilities values have been calculated along with the exploration of nonlinear optical properties of the title compound. DFT computed total first static hyperpolarizability (β0 = 0.2747 × 10-30 esu) indicates that title molecule could be an area of interest as an attractive future NLO material. For the analysis of thermal behaviour of title molecule, thermodynamic properties such as heat capacity, entropy and enthalpy change at various temperatures have been calculated. The NBO computations were done for the correlation of possible transitions with the electronic transitions. Electrophilic and nucleophilic regions were identified with the help of MESP plot. Determination of energy gap has been done by using HOMO and LUMO energy values, along with the computation of electronegativity and electrophilicity indices.

Conformational analysis of capsaicin using 13C, 15N MAS NMR, GIAO DFT and GA calculations

NASA Astrophysics Data System (ADS)

Siudem, Paweł; Paradowska, Katarzyna; Bukowicki, Jarosław

2017-10-01

Capsaicin produced by plants from genus Capsicum exerts multiple pharmacological effects and has found applications in food and pharmaceutical industry. The alkaloid was studied by a combined approach: solid-state NMR, GA conformational search and GIAO DFT methods. The 13C CPMAS NMR spectra were recorded using variable contact time and dipolar dephasing experiments. The results of cross-polarization (CP) kinetics, such as TCP values and long T1ρH (100-200 ms), indicated that the capsaicin molecule is fairly mobile, especially at the end of the aliphatic chain. The15N MAS NMR spectrum showed one narrow signal at -255 ppm. Genetic algorithm (GA) search with multi modal optimization was used to find low-energy conformations of capsaicin. Theoretical GIAO DFT calculations were performed using different basis sets to characterize five selected conformations. 13C CPMAS NMR was used as a validation method and the experimental chemical shifts were compared with those calculated for selected stable conformers. Conformational analysis suggests that the side chain can be bent or extended. A comparison of the experimental and the calculated chemical shifts indicates that solid capsaicin does not have the same structure as those established by PWXRD.

Study of the docking of competitive inhibitors at a model of tyrosinase active site: insights from joint broken-symmetry/Spin-Flip DFT computations and ELF topological analysis

PubMed Central

de la Lande, A.; Maddaluno, J.; Parisel, O.; Darden, T. A.; Piquemal, J-P

2010-01-01

Following our previous study (Piquemal et al., New J. Chem., 2003, 27, 909), we present here a DFT study of the inhibition of the Tyrosinase enzyme. Broken-symmetry DFT computations are supplemented with Spin-Flip TD-DFT calculations, which, for the first time, are applied to such a dicopper enzyme. The chosen biomimetic model encompasses a dioxygen molecule, two Cu(II) cations, and six imidazole rings. The docking energy of a natural substrate, namely phenolate, together with those of several inhibitor and non-inhibitor compounds, are reported and show the ability of the model to rank the most potent inhibitors in agreement with experimental data. With respect to broken-symmetry calculations, the Spin-Flip TD-DFT approach reinforces the possibility for theory to point out potent inhibitors: the need for the deprotonation of the substrates, natural or inhibitors, is now clearly established. Moreover, Electron Localization Function (ELF) topological analysis computations are used to deeply track the particular electronic distribution of the Cu-O-Cu three-center bonds involved in the enzymatic Cu2O2 metallic core (Piquemal and Pilmé, J. Mol. Struct.: Theochem, 2006, 77, 764). It is shown that such bonds exhibit very resilient out-of-plane density expansions that play a key role in docking interactions: their 3D-orientation could be the topological electronic signature of oxygen activation within such systems. PMID:20396590

DFT +U Modeling of Hole Polarons in Organic Lead Halide Perovskites

NASA Astrophysics Data System (ADS)

Welch, Eric; Erhart, Paul; Scolfaro, Luisa; Zakhidov, Alex

Due to the ever present drive towards improved efficiencies in solar cell technology, new and improved materials are emerging rapidly. Organic halide perovskites are a promising prospect, yet a fundamental understanding of the organic perovskite structure and electronic properties is missing. Particularly, explanations of certain physical phenomena, specifically a low recombination rate and high mobility of charge carriers still remain controversial. We theoretically investigate possible formation of hole polarons adopting methodology used for oxide perovskites. The perovskite studied here is the ABX3structure, with A being an organic cation, B lead and C a halogen; the combinations studied allow for A1,xA2 , 1 - xBX1,xX2 , 3 - xwhere the alloy convention is used to show mixtures of the organic cations and/or the halogens. Two organic cations, methylammonium and formamidinium, and three halogens, iodine, chlorine and bromine are studied. Electronic structures and polaron behavior is studied through first principle density functional theory (DFT) calculations using the Vienna Ab Initio Simulation Package (VASP). Local density approximation (LDA) pseudopotentials are used and a +U Hubbard correction of 8 eV is added; this method was shown to work with oxide perovskites. It is shown that a localized state is realized with the Hubbard correction in systems with an electron removed, residing in the band gap of each different structure. Thus, hole polarons are expected to be seen in these perovskites.

Theoretical simulations on the antioxidant mechanism of naturally occurring flavonoid: A DFT approach

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

Praveena, R.; Sadasivam, K.

Synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are found to be toxic, hence non-carcinogenic naturally occurring radical scavengers especially flavonoids have gained considerable importance in the past two decades. In the present investigation, the radical scavenging activity of C-glycosyl flavonoids is evaluated using theoretical approach which could broaden its scope in therapeutic applications. Gas and solvent phase studies of structural and molecular characteristics of C-glycosyl flavonoid, isovitexin is investigated through hydrogen atom transfer mechanism (HAT), Electron transfer-proton transfer (ET–PT) and Sequential proton loss electron transfer (SPLET) by Density functional theory (DFT) using hybrid parameters. The computedmore » values of the adiabatic ionization potential, electron affinity, hardness, softness, electronegativity and electrophilic index indicate that isovitexin possess good radical scavenging activity. The behavior of different –OH groups in polyphenolic compounds is assessed by considering electronic effects of the neighbouring groups and the overall geometry of molecule which in turn helps in analyzing the antioxidant capacity of the polyphenolic molecule. The studies indicate that the H–atom abstraction from 4’–OH site is preferred during the radical scavenging process. From Mulliken spin density analysis and FMOs, B–ring is found to be more delocalized center and capable of electron donation. Comparison of antioxidant activity of vitexin and isovitexin leads to the conclusion that isovitexin acts as a better radical scavenger. This is an evidence for the importance of position of glucose unit in the flavonoid.« less

Investigation of copper(II) binding to the protein precursor of Non-Amyloid-Beta Component of Alzheimer Disease Amyloid Plaque

NASA Astrophysics Data System (ADS)

Rose, Francis; Hodak, Miroslav; Bernholc, Jerry

2007-03-01

The Non-Amyloid-Beta Component Precursor (NACP) is a natively unfolded synaptic protein that is implicated in Alzheimers and Parkinsons diseases. Its aggregation into fibrillar structures is accelerated by the binding of copper(II). Experimental studies suggest that the dominant copper binding site is located at the histidine residue in NACP. Based on this evidence we assembled a model fragment of the binding site and used DFT to analyze the conformational details of the most probable binding motifs. We investigated the overall conformational effects with classical MD by constraining the copper binding site to the most energetically favorable geometry obtained from the DFT calculations. These results are compared and contrasted with those of the unbound NACP.

Experimental and theoretical investigation of relative optical band gaps in graphene generations

NASA Astrophysics Data System (ADS)

Bhatnagar, Deepika; Singh, Sukhbir; Yadav, Sriniwas; Kumar, Ashok; Kaur, Inderpreet

2017-01-01

Size and chemical functionalization dependant optical band gaps in graphene family nanomaterials were investigated by experimental and theoretical study using Tauc plot and density functional theory (DFT). We have synthesized graphene oxide through a modified Hummer’s method using graphene nanoplatelets and sequentially graphene quantum dots through hydrothermal reduction. The experimental results indicate that the optical band gap in graphene generations was altered by reducing the size of graphene sheets and attachment of chemical functionalities like epoxy, hydroxyl and carboxyl groups plays a crucial role in varying optical band gaps. It is further confirmed by DFT calculations that the π orbitals were more dominatingly participating in transitions shown by projected density of states and the molecular energy spectrum represented the effect of attached functional groups along with discreteness in energy levels. Theoretical results were found to be in good agreement with experimental results. All of the above different variants of graphene can be used in native or modified form for sensor design and optoelectronic applications.

Ethylene dissociation on flat and stepped Ni(1 1 1): A combined STM and DFT study

NASA Astrophysics Data System (ADS)

Vang, Ronnie T.; Honkala, Karoliina; Dahl, Søren; Vestergaard, Ebbe K.; Schnadt, Joachim; Lægsgaard, Erik; Clausen, Bjerne S.; Nørskov, Jens K.; Besenbacher, Flemming

2006-01-01

The dissociative adsorption of ethylene (C 2H 4) on Ni(1 1 1) was studied by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The STM studies reveal that ethylene decomposes exclusively at the step edges at room temperature. However, the step edge sites are poisoned by the reaction products and thus only a small brim of decomposed ethylene is formed. At 500 K decomposition on the (1 1 1) facets leads to a continuous growth of carbidic islands, which nucleate along the step edges. DFT calculations were performed for several intermediate steps in the decomposition of ethylene on both Ni(1 1 1) and the stepped Ni(2 1 1) surface. In general the Ni(2 1 1) surface is found to have a higher reactivity than the Ni(1 1 1) surface. Furthermore, the calculations show that the influence of step edge atoms is very different for the different reaction pathways. In particular the barrier for dissociation is lowered significantly more than the barrier for dehydrogenation, and this is of great importance for the bond-breaking selectivity of Ni surfaces. The influence of step edges was also probed by evaporating Ag onto the Ni(1 1 1) surface. STM shows that the room temperature evaporation leads to a step flow growth of Ag islands, and a subsequent annealing at 800 K causes the Ag atoms to completely wet the step edges of Ni(1 1 1). The blocking of the step edges is shown to prevent all decomposition of ethylene at room temperature, whereas the terrace site decomposition at 500 K is confirmed to be unaffected by the Ag atoms. Finally a high surface area NiAg alloy catalyst supported on MgAl 2O 4 was synthesized and tested in flow reactor measurements. The NiAg catalyst has a much lower activity for ethane hydrogenolysis than a similar Ni catalyst, which can be rationalized by the STM and DFT results.

Spectroscopic investigation (FTIR spectrum), NBO, HOMO-LUMO energies, NLO and thermodynamic properties of 8-Methyl-N-vanillyl-6-nonenamideby DFT methods

NASA Astrophysics Data System (ADS)

Sherin Percy Prema Leela, J.; Hemamalini, R.; Muthu, S.; Al-Saadi, Abdulaziz A.

2015-07-01

Capsicum a hill grown vegetable is also known as red pepper or chili pepper. Capsaicin(8-Methyl-N-vanillyl-6-nonenamide) is the active component in chili peppers, which is currently used in the treatment of osteoarthritis, psoriasis and cancer. Fourier transform infrared (FT-IR) spectrum of Capsaicin in the solid phase were recorded in the region 4000-400 cm-1 and analyzed. The vibrational frequencies of the title compound were obtained theoretically by DFT/B3LYP calculations employing the standard 6-311++G(d,p) basis set and were compared with Fourier transform infrared spectrum. Complete vibrational assignment 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. Stability of the molecule arising from hyper conjugative interactions, charge delocalization and intra molecular hydrogen bond-like weak interaction has been analyzed using Natural bond orbital (NBO) analysis by using B3LYP/6-311++G(d,p) method. The results show that electron density (ED) in the σ∗ and π∗ antibonding orbitals and second-order delocalization energies E (2) confirm the occurrence of intra molecular charge transfer (ICT) within the molecule. The dipole moment (μ), polarizability (α) and the hyperpolarizability (β) values of the molecule has been computed. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated.

Predicting the NMR spectra of nucleotides by DFT calculations: cyclic uridine monophosphate.

PubMed

Bagno, Alessandro; Rastrelli, Federico; Saielli, Giacomo

2008-06-01

We present an experimental and quantum chemical NMR study of the mononucleotide cyclic uridine monophosphate in water. Spectral parameters ((1)H and (13)C chemical shifts and (1)H--(1)H, (13)C--(1)H, (31)P--(13)C and (31)P--(1)H spin-spin coupling constants) have been carefully obtained experimentally and calculated using DFT methods including the solvent effect and the conformational flexibility of the solute. This study confirms that the (1)H and (13)C spectra of polar, flexible molecules in aqueous solution can be predicted with a high level of accuracy, comparable to that obtained for less complex systems. Copyright (c) 2008 John Wiley & Sons, Ltd

Imaging of the outer valence orbitals of CO by electron momentum spectroscopy — Comparison with high level MRSD-CI and DFT calculations

NASA Astrophysics Data System (ADS)

Fan, X. W.; Chen, X. J.; Zhou, S. J.; Zheng, Y.; Brion, C. E.; Frey, R.; Davidson, E. R.

1997-09-01

A newly constructed energy dispersive multichannel electron momentum spectrometer has been used to image the electron density of the outer valence orbitals of CO with high precision. Binding energy spectra are obtained at a coincidence energy resolution of 1.2 eV fwhm. The measured electron density profiles in momentum space for the outer valence orbitals of CO are compared with cross sections calculated using SCF wavefunctions with basis sets of varying complexity up to near-Hartree-Fock limit in quality. The effects of correlation and electronic relaxation on the calculated momentum profiles are investigated using large MRSD-CI calculations of the full ion-neutral overlap distributions, as well as large basis set DFT calculations with local and non-local (gradient corrected) functionals.

Spectral analysis and DFT computations of the hydrogen bonded complex between 2,6-diaminopyridine with 2,6-dichloro-4-nitrophenol in different solvents

NASA Astrophysics Data System (ADS)

Al-Ahmary, Khairia M.; Soliman, Saied M.; Habeeb, Moustafa M.; Al-Obidan, Areej H.

2017-09-01

New hydrogen bonded complex between 2,6-dichloro-4-nitrophenol (DCNP), proton donor with the proton acceptor 2,6-diaminopyridine (DAP) has been synthesized and characterized in solution and solid state by different spectroscopic techniques. Electronic spectra were used to identify the novel proton transfer complex through appearance of new absorption bands in acetonitrile (CH3CN), methanol (CH3OH) and mixture composed from 1:1 methanol and acetonitrile (AN-Me). The complex stoichiometry was determined to be 1:1 by job's method and photometric titrations. The formation constant was determined by applying minimum-maximum absorbances method where it reached high values confirming the complex high stability. A spectroscopic method for determining DAP was presented and validated statistically. The solid complex was characterized by elemental analysis, infrared and 1H NMR studies where the hydrogen bonded reaction occurs between the phenolic OH with the pyridine ring nitrogen as well as one amino group of DNP. The density functional theory DFT (B3LYP) method has been used to energy optimization of the reactants and complex in the ground state using two basis sets 6-31G(d) and 6-31 G+(d,p). The first one led to energy optimized structure through bifurcated hydrogen bond between OH of DCNP with the ring nitrogen and one amino group of DAP with optimization energy -1998.7 Hartree. The second one gave an optimized structure thought hydrogen bonding between OH and one amino group with lowered optimization energy -2018.1 Hartree. Hence, the experimental results will be simulated with the most stable one at DFT/B3LYB 6-31G+ (d,p). The most reactive electrophilic and nucleophilic sites of DCNP and DAP were predicted using the molecular electrostatic potential. The theoretical electronic spectra in the gas phase and the investigated solvents were calculated at TD-DFT/B3LYP 6-31G+ (d,p) and compared with measured electronic spectra where a satisfactory results have been obtained

Density Functional Theory (DFT) Simulations of Shocked Liquid Xenon

NASA Astrophysics Data System (ADS)

Mattsson, Thomas R.; Magyar, Rudolph J.

2009-06-01

Xenon is not only a technologically important element used in laser technologies and jet propulsion, but it is also one of the most accessible materials in which to study the metal-insulator transition with increasing pressure. Because of its closed shell electronic configuration, Xenon is often assumed to be chemically inert, interacting almost entirely through the van der Waals interaction, and at liquid density, is typically modeled well using Leonard-Jones potentials. However, such modeling has a limited range of validity as Xenon is known to form compounds at normal conditions and likely exhibits considerably more chemistry at higher densities when hybridization of occupied orbitals becomes significant. In this talk, we present DFT-MD simulations of shocked liquid Xenon with the goal of developing an improved equation of state. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Optical properties of alkali halide crystals from all-electron hybrid TD-DFT calculations

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

Webster, R., E-mail: ross.webster07@imperial.ac.uk; Harrison, N. M.; Bernasconi, L.

2015-06-07

We present a study of the electronic and optical properties of a series of alkali halide crystals AX, with A = Li, Na, K, Rb and X = F, Cl, Br based on a recent implementation of hybrid-exchange time-dependent density functional theory (TD-DFT) (TD-B3LYP) in the all-electron Gaussian basis set code CRYSTAL. We examine, in particular, the impact of basis set size and quality on the prediction of the optical gap and exciton binding energy. The formation of bound excitons by photoexcitation is observed in all the studied systems and this is shown to be correlated to specific features ofmore » the Hartree-Fock exchange component of the TD-DFT response kernel. All computed optical gaps and exciton binding energies are however markedly below estimated experimental and, where available, 2-particle Green’s function (GW-Bethe-Salpeter equation, GW-BSE) values. We attribute this reduced exciton binding to the incorrect asymptotics of the B3LYP exchange correlation ground state functional and of the TD-B3LYP response kernel, which lead to a large underestimation of the Coulomb interaction between the excited electron and hole wavefunctions. Considering LiF as an example, we correlate the asymptotic behaviour of the TD-B3LYP kernel to the fraction of Fock exchange admixed in the ground state functional c{sub HF} and show that there exists one value of c{sub HF} (∼0.32) that reproduces at least semi-quantitatively the optical gap of this material.« less

Spectroscopic, DFT, and XRD Studies of Hydrogen Bonds in N-Unsubstituted 2-Aminobenzamides.

PubMed

Mphahlele, Malose Jack; Maluleka, Marole Maria; Rhyman, Lydia; Ramasami, Ponnadurai; Mampa, Richard Mokome

2017-01-04

The structures of the mono- and the dihalogenated N -unsubstituted 2-aminobenzamides were characterized by means of the spectroscopic (¹H-NMR, UV-Vis, FT-IR, and FT-Raman) and X-ray crystallographic techniques complemented with a density functional theory (DFT) method. The hindered rotation of the C(O)-NH₂ single bond resulted in non-equivalence of the amide protons and therefore two distinct resonances of different chemical shift values in the ¹H-NMR spectra of these compounds were observed. 2-Amino-5-bromobenzamide ( ABB ) as a model confirmed the presence of strong intramolecular hydrogen bonds between oxygen and the amine hydrogen. However, intramolecular hydrogen bonding between the carbonyl oxygen and the amine protons was not observed in the solution phase due to a rapid exchange of these two protons with the solvent and fast rotation of the Ar-NH₂ single bond. XRD also revealed the ability of the amide unit of these compounds to function as a hydrogen bond donor and acceptor simultaneously to form strong intermolecular hydrogen bonding between oxygen of one molecule and the NH moiety of the amine or amide group of the other molecule and between the amine nitrogen and the amide hydrogen of different molecules. DFT calculations using the B3LYP/6-311++G(d,p) basis set revealed that the conformer ( A ) with oxygen and 2-amine on the same side predominates possibly due to the formation of a six-membered intramolecular ring, which is assisted by hydrogen bonding as observed in the single crystal XRD structure.

A study of vibrational spectra and investigations of charge transfer and chemical bonding features of 2-chloro benzimidazole based on DFT computations

NASA Astrophysics Data System (ADS)

Muthunatesan, S.; Ragavendran, V.

2015-01-01

Benzimidazoles are bicyclic heteroatomic molecules. Polycyclic heteroatomic molecules have extensive coupling of different modes leading to strong coupling of force constants associated with the various chemical bonds of the molecules. To carry out a detailed vibrational spectroscopic analysis of such a bicyclic heteroatomic molecule, FT-IR and FT-Raman spectra of 2-chloro benzimidazole (CBZ) have been recorded in the condensed phase. Density Functional Theory calculations in the B3LYP/6-31G* level have been carried out to determine the optimized geometry and vibrational frequencies. In order to obtain a close agreement between theoretical and observed frequencies and hence to perform a reliable assignment, the theoretical DFT force field was transformed from Cartesian to local symmetry co-ordinates and then scaled empirically using SQM methodology. The SQM treatment resulted in a RMS deviation of 9.4 cm-1. For visual comparison, the observed and calculated spectra are presented on a common wavenumber scale. From the NBO analysis, the electron density (ED) charge transfers in the σ* and π* antibonding orbitals and second order delocalization energies E(2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. The calculated Homo and Lumo energies show that charge transfer occurs within the molecule. The results obtained from the vibrational, NBO and HOMO-LUMO analyses have been properly tabulated.

Spectroscopic (FT-IR, FT-Raman and UV-Visible) investigations, NMR chemical shielding anisotropy (CSA) parameters of 2,6-Diamino-4-chloropyrimidine for dye sensitized solar cells using density functional theory.

PubMed

Gladis Anitha, E; Joseph Vedhagiri, S; Parimala, K

2015-02-05

The molecular structure, geometry optimization, vibrational frequencies of organic dye sensitizer 2,6-Diamino-4-chloropyrimidine (DACP) were studied based on Hartree-Fock (HF) and density functional theory (DFT) using B3LYP methods with 6-311++G(d,p) basis set. Ultraviolet-Visible (UV-Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the UV-Visible regions were assigned based on TD-DFT calculation. The absorption bands are assigned to transitions. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer DACP is due to an electron injection process from excited dye to the semiconductor's conduction band. The observed and the calculated frequencies are found to be in good agreement. The energies of the frontier molecular orbitals (FMOS) have also been determined. The chemical shielding anisotropic (CSA) parameters are calculated from the NMR analysis, Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Copyright © 2014 Elsevier B.V. All rights reserved.

MCD spectroscopy and TD-DFT calculations of low symmetry subnaphthalocyanine analogs.

PubMed

Mack, John; Otaki, Tatsuya; Durfee, William S; Kobayashi, Nagao; Stillman, Martin J

2014-07-01

Magnetic circular dichroism (MCD) spectroscopy and time-dependent density functional theory (TD-DFT) calculations are used to analyze the electronic structure and optical properties of low-symmetry subnaphthalocyanine analogs with AAB and ABB structures formed during mixed condensations of tetrafluorophthalonitrile and 2,3-naphthalenedicarbonitrile. The results demonstrate that trends observed in the properties of phthalocyanine analogs can be used to fine tune the optical properties so that the Q(0,0) bands lie in the red region, in a manner that does not significantly destabilize the highest occupied molecular orbital (HOMO) energy relative to that of the parent subphthalocyanine ligand. Attempts to study the spectroscopy of anion radical species proved unsuccessful, since they proved to be unstable. Copyright © 2014 Elsevier Inc. All rights reserved.

Using Density Functional Theory (DFT) for the Calculation of Atomization Energies

NASA Technical Reports Server (NTRS)

Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)

1995-01-01

The calculation of atomization energies using density functional theory (DFT), using the B3LYP hybrid functional, is reported. The sensitivity of the atomization energy to basis set is studied and compared with the coupled cluster singles and doubles approach with a perturbational estimate of the triples (CCSD(T)). Merging the B3LYP results with the G2(MP2) approach is also considered. It is found that replacing the geometry optimization and calculation of the zero-point energy by the analogous quantities computed using the B3LYP approach reduces the maximum error in the G2(MP2) approach. In addition to the 55 G2 atomization energies, some results for transition metal containing systems will also be presented.

Anharmonic vibrational spectroscopy, NBO charges and global chemical reactivity studies on the charge transfer PDCA-.AHMP+ single crystal using DFT calculations

NASA Astrophysics Data System (ADS)

Faizan, Mohd; Afroz, Ziya; Bhat, Sheeraz Ahmad; Alam, Mohamad Jane; Ahmad, Shabbir; Ahmad, Afaq

2018-04-01

The charge transfer (CT) complex of the 2-amino-4-hydroxy-6-methylpyrimidine and 2,3 pyrazinedicarboxylic acid (PDCA-.AHMP+) was synthesized and its single crystal was grown by solution method. The structure of the crystalline complex has been investigated by single crystal X-ray diffraction (SCXRD). The vibrational features of the complex have been studied with the help of FTIR spectra and DFT computation. The anharmonic corrections in vibrational frequencies are made using the GVPT2 method at B3LYP/6-311++G(d,p) level of theory. The frontier molecular orbitals and global chemical reactivity have been calculated to understand the pharmacological aspect of the synthesized crystal. Furthermore, Hirshfeld electrostatic potential (ESP) surface, void space in the crystal structure and natural as well as Mulliken atomic charges are studied.

Electronic Properties of Cyclacenes from TAO-DFT

PubMed Central

Wu, Chun-Shian; Lee, Pei-Yin; Chai, Jeng-Da

2016-01-01

Owing to the presence of strong static correlation effects, accurate prediction of the electronic properties (e.g., the singlet-triplet energy gaps, vertical ionization potentials, vertical electron affinities, fundamental gaps, symmetrized von Neumann entropy, active orbital occupation numbers, and real-space representation of active orbitals) of cyclacenes with n fused benzene rings (n = 4–100) has posed a great challenge to traditional electronic structure methods. To meet the challenge, we study these properties using our newly developed thermally-assisted-occupation density functional theory (TAO-DFT), a very efficient method for the study of large systems with strong static correlation effects. Besides, to examine the role of cyclic topology, the electronic properties of cyclacenes are also compared with those of acenes. Similar to acenes, the ground states of cyclacenes are singlets for all the cases studied. In contrast to acenes, the electronic properties of cyclacenes, however, exhibit oscillatory behavior (for n ≤ 30) in the approach to the corresponding properties of acenes with increasing number of benzene rings. On the basis of the calculated orbitals and their occupation numbers, the larger cyclacenes are shown to exhibit increasing polyradical character in their ground states, with the active orbitals being mainly localized at the peripheral carbon atoms. PMID:27853249

A series of 2, 4, 5-trisubstituted oxazole: Synthesis, characterization and DFT modelling

NASA Astrophysics Data System (ADS)

Kadam, Vinay S.; Shaikh, Saminaparwin G.; Patel, Arun L.

2016-06-01

A new series of 2,4,5-trisubstituted oxazole were synthesized with good yields using simple methodology. All the compounds were thoroughly characterized by IR, NMR (1H and 13C) and mass spectrometry and structures of 2-(4-butyloxyphenyl)-4,5-dimethyloxazole (5b) and 4,5-dimethyl-2-(4-(octyloxy)phenyl)oxazole(5e) were unambiguously determined by X-ray crystallography. Evidently, the crystal structures of these compounds showed C-H⋯N and C-H⋯O intermolecular interactions. The electronic structures of these compounds were also studied by DFT at B3LYP/6-311G ++ level of theory.

An insight into the origin of room-temperature ferromagnetism in SnO2 and Mn-doped SnO2 quantum dots: an experimental and DFT approach.

PubMed

Manikandan, Dhamodaran; Boukhvalov, D W; Amirthapandian, S; Zhidkov, I S; Kukharenko, A I; Cholakh, S O; Kurmaev, E Z; Murugan, Ramaswamy

2018-02-28

SnO 2 and Mn-doped SnO 2 single-phase tetragonal crystal structure quantum dots (QDs) of uniform size with control over dopant composition and microstructure were synthesized using the high pressure microwave synthesis technique. On a broader vision, we systematically investigated the influence of dilute Mn ions in SnO 2 under the strong quantum confinement regime through various experimental techniques and density functional theoretical (DFT) calculations to disclose the physical mechanism governing the observed ferromagnetism. DFT calculations revealed that the formation of the stable (001) surface was much more energetically favorable than that of the (100) surface, and the formation energy of the oxygen vacancies in the stable (001) surface was comparatively higher in the undoped SnO 2 QDs. X-ray photoelectron spectroscopy (XPS) and first-principles modeling of doped QDs revealed that the lower doping concentration of Mn favored the formation of MnO-like (Mn 2+ ) structures in defect-rich areas and the higher doping concentration of Mn led to the formation of multiple configurations of Mn (Mn 2+ and Mn 3+ ) in the stable surfaces of SnO 2 QDs. Electronic absorption spectra indicated the characteristic spin allowed ligand field transitions of Mn 2+ and Mn 3+ and the red shift in the band gap. DFT calculations clearly indicated that only the substitutional dopant antiferromagnetic configurations were more energetically favorable. The gradual increase of magnetization at a low level of Mn-doping could be explained by the prevalence of antiferromagnetic manganese-vacancy pairs. Higher concentrations of Mn led to the appearance of ferromagnetic interactions between manganese and oxygen vacancies. The increase in the concentration of metallic dopants caused not just an increase in the total magnetic moment of the system but also changed the magnetic interactions between the magnetic moments on the metal ions and oxygen. The present study provides new insight into the

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.

Adsorption behavior and mechanism of acidic blue 25 dye onto cucurbit[8]uril: A spectral and DFT study

NASA Astrophysics Data System (ADS)

Luo, Hanhan; Huang, Xiangyu; Luo, Yuhan; Li, Zhuang; Li, Lan; Gao, Chao; Xiong, Jinyan; Li, Wei

2018-03-01

The acidic blue 25 (AB25) dye was efficiently adsorbed by CB [8]; the saturated adsorption capacity (qexp) reached 434.8 mg/g and was far higher than those of previous reported adsorbents. The Langmuir and Freundich isotherms were used to fit the equilibrium data, and the results showed that the Freundlich isotherm seemed to agree better with the AB25 adsorption. The adsorption kinetics followed the pseudo-second-order model. Calculated thermodynamic parameters showed that the adsorption of AB25 onto CB [8] was a spontaneous and enthalpy-driven process. The adsorption mechanism was explored by N2 adsorption-desorption, TG, FT-IR, UV-vis as well as MD simulation and DFT calculations. TG analysis revealed that a new inclusion complex was produced, and FT-IR,UV-vis spectrum and DFT calculations verify its structure. In this inclusion complex, the AB25 dye molecule inserted into cavities of CB [8] from portal, and the sulfonate and phenyl groups stayed in the hydrophobic cavity. TDDFT calculations indicated that all excitation arisen from π → π* transition.

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.

Structure and electronic absorption spectra of nematogenic alkoxycinnamic acids - a comparative study based on semiempirical and DFT methods.

PubMed

Praveen, Pogula Lakshmi; Ojha, Durga Prasad

2012-04-01

Structure of nematogenic p-n-Alkoxy cinnamic acids (nOCAC) with various alkyl chain carbon atoms (n = 2, 4, 6, 8) has been optimized using density functional B3LYP with 6-31+G (d) basis set using crystallographic geometry as input. Using the optimized geometry, electronic structure of the molecules has been evaluated using the semiempirical methods and DFT calculations. Molecular charge distribution and phase stability of these systems have been analyzed based on Mulliken and Löwdin population analysis. The electronic absorption spectra of nOCAC molecules have been simulated by employing DFT method, semiempirical CNDO/S and INDO/S parameterizations. Two types of calculations have been performed for model systems containing single and double molecules of nOCAC. UV-Visible spectra have been calculated for all single molecules. The UV stability of the molecules has been discussed in light of the electronic transition oscillator strength (f). The dimer complexes of higher homologues (n = 6, 8) have also been reported to enable the comparison between single and double molecules.

One pot synthesis of Curcumin-NSAIDs prodrug, spectroscopic characterization, conformational analysis, chemical reactivity, intramolecular interactions and first order hyperpolarizability by DFT method

NASA Astrophysics Data System (ADS)

Srivastava, Sangeeta; Gupta, Preeti; Sethi, Arun; Singh, Ranvijay Pratap

2016-08-01

A novel Curcumin-NSAIDs prodrug 4-((1E, 3Z, 6E)-3-hydroxy-(4-hydroxy-3-methoxyphenyl)-5-oxohepta-1,3,3-trienyl)-2-methoxyphenyl-2-(4-isobutylphenyl) propanoate (2) derivative was synthesized by Steglich esterification in high yield and characterized with the help of 1H, 13C NMR, 1H-1H COSY, UV, FT-IR spectroscopy and mass spectrometry. The molecular geometry of synthesized compound was calculated in ground state by Density functional theory (DFT/B3LYP) using two different basis set 6-31G (d, p) and 6-311G (d, p). Conformational analysis of 2 was carried out to determine the most stable conformation. Stability of the molecule as a result of hyperconjugative interactions and electron delocalization were analysed using Natural bond orbital (NBO) analysis. Intramolecular interactions were analysed by AIM (Atom in molecule) approach. Global and local reactivity descriptors were calculated to study the reactive site within molecule. The electronic properties such as HOMO and LUMO energies were calculated using time dependent Density Functional Theory (TD-DFT). The vibrational wavenumbers were calculated using DFT method and assigned with the help of potential energy distribution (PED). First hyperpolarizability value has been calculated to describe the nonlinear optical (NLO) property of the synthesized compound. Molecular electrostatic potential (MEP) for synthesized compounds have also been determined to check their electrophilic or nucleophilic reactivity.

Experimental and theoretical investigation of [Al(PCr)(H2O)] complex in aqueous solution

NASA Astrophysics Data System (ADS)

Tenório, Thaís; Lopes, Damiana C. N.; Silva, Andréa M.; Ramos, Joanna Maria; Buarque, Camilla D.

2014-01-01

Phosphocreatine is a phosphorylated creatine molecule synthesized in the liver and transported to muscle cells where it is used for the temporary storage of energy. In Alzheimer's disease, the capture of glucose by cells is impaired, which negatively affects the Krebs cycle, leading to problems with the generation of phosphocreatine. Furthermore, the creatine-phosphocreatine system, regulated by creatine kinase, is affected in the brains of Alzheimer's disease patients. Aluminum ions are associated with Alzheimer's disease. Al(III) decreases cell viability and increases the fluidity of the plasma membrane, profoundly altering cell morphology. In this study, one of the complexes formed by Al(III) and phosphocreatine in aqueous solution was investigated by potentiometry, 31P and 27Al NMR, Raman spectroscopy and density functional theory (DFT) calculations. The log KAlPCr value was 11.37 ± 0.03. Phosphocreatine should act as a tridentate ligand in this complex. The 27Al NMR peak at 48.92 ppm indicated a tetrahedral molecule. The fourth position in the arrangement was occupied by a coordinated water molecule. Raman spectroscopy, 31P NMR and DFT calculations (DFT:B3LYP/6-311++G**) indicated that the donor atoms are oxygen in the phosphate group, the nitrogen of the guanidine group and the oxygen of the carboxylate group. Mulliken charges, NBO charges, frontier molecular orbitals, electrostatic potential contour surfaces and mapped electrostatic potential were also examined.

FTIR, FT-Raman, FT-NMR, UV-visible and quantum chemical investigations of 2-amino-4-methylbenzothiazole.

PubMed

Arjunan, V; Sakiladevi, S; Rani, T; Mythili, C V; Mohan, S

2012-03-01

The FT-IR (4000-400 cm(-1)) and FT-Raman (4000-100 cm(-1)) spectral measurements and complete assignments of the observed spectra of 2-amino-4-methylbenzothiazole (2A4MBT) have been proposed. Ab initio and DFT calculations have been performed and the structural parameters of the compound were determined from the optimised geometry with 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets and giving energies, harmonic vibrational frequencies, depolarisation ratios, IR intensities and Raman activities. (1)H and (13)C NMR spectra were recorded and (1)H and (13)C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO, LUMO and band gap energies were measured by time-dependent DFT (TD-DFT) approach. The geometric parameters, energies, harmonic vibrational frequencies, IR intensities, Raman activities chemical shifts and absorption wavelengths were compared with the available experimental data of the molecule. The influences of methyl and amino groups on the skeletal modes and on the proton chemical shifts have been investigated. Copyright © 2011 Elsevier B.V. All rights reserved.

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.

Molecular structure, vibrational analysis (IR and Raman) and quantum chemical investigations of 1-aminoisoquinoline

NASA Astrophysics Data System (ADS)

Sivaprakash, S.; Prakash, S.; Mohan, S.; Jose, Sujin P.

2017-12-01

Quantum chemical calculations of energy and geometrical parameters of 1-aminoisoquinoline [1-AIQ] were carried out by using DFT/B3LYP method using 6-311G (d,p), 6-311G++(d,p) and cc-pVTZ basis sets. The vibrational wavenumbers were computed for the energetically most stable, optimized geometry. The vibrational assignments were performed on the basis of potential energy distribution (PED) using VEDA program. The NBO analysis was done to investigate the intra molecular charge transfer of the molecule. The frontier molecular orbital (FMO) analysis was carried out and the chemical reactivity descriptors of the molecule were studied. The Mulliken charge analysis, molecular electrostatic potential (MEP), HOMO-LUMO energy gap and the related properties were also investigated at B3LYP level. The absorption spectrum of the molecule was studied from UV-Visible analysis by using time-dependent density functional theory (TD-DFT). Fourier Transform Infrared spectrum (FT-IR) and Raman spectrum of 1-AIQ compound were analyzed and recorded in the range 4000-400 cm-1 and 3500-100 cm-1 respectively. The experimentally determined wavenumbers were compared with those calculated theoretically and they complement each other.

DFT modeling, UV-Vis and IR spectroscopic study of acetylacetone-modified zirconia sol-gel materials.

PubMed

Georgieva, Ivelina; Danchova, Nina; Gutzov, Stoyan; Trendafilova, Natasha

2012-06-01

Theoretical and spectroscopic studies of a series of monomeric and dimeric complexes formed through the modification of a zirconium butoxide precursor with acetylacetone and subsequent hydrolysis and/or condensation have been performed by applying DFT/B3LYP/6-31++G(d) and highly accurate RI-ADC(2) methods as well as IR and UV-Vis transmittance and diffuse reflectance spectroscopies. Based on DFT model calculations and simulated and experimental UV-Vis and IR spectra of all the studied structures, the most probable building units of the Zr(IV)-AcAc gel were predicted: the dimeric double hydroxo-bridged complex Zr(2)(AcAc)(2)(OH)(4)(OH)(2br) 9 and the monooxo-bridged complex Zr(2)(AcAc)(2)(OH)(4)O(br)·2H(2)O 12. In both structures, the two AcAc ligands are coordinated to one Zr atom. It was shown that building units 9 and 12 determine the photophysical and vibrational properties of the gel material. The observed UV-Vis and IR spectra of Zr(IV)-AcAc gel were interpreted and a relation between the spectroscopic and structural data was derived. The observed UV-Vis bands at 315 nm and 298/288 nm were assigned to partial ligand-metal transitions and to intra-/inter-AcAc ligand transitions, respectively.

Synthesis, characterization and DFT studies of two new silver(I) complexes with 3,4-lutidine

NASA Astrophysics Data System (ADS)

Soliman, Saied M.; Assem, Rania; Abu-Youssef, Morsy A. M.; Kassem, Taher S.

2015-04-01

The synthesis, characterization and molecular structure of two new Ag(I) complexes with 3,4-lutidine (34lut) have been reported. The [Ag(34lut)3(OAC)]; 1 and [Ag(34lut)2(TFA)]; 2 complexes, where OAC and TFA are acetate and trifluoroacetate respectively, have been characterized using elemental analysis, FTIR, NMR and mass spectra. Their molecular structures were calculated using DFT quantum chemical calculations. Both 1 and 2 were found to have distorted tetrahedral geometry around the Ag(I). The spectroscopic properties of the studied complexes have been calculated using the same level of theory. The Infrared vibrational frequencies of the COO stretches confirmed that the OAC is monodentate in 1 while the TFA is bidentate in 2. The calculated polarizability (α0) and HOMO-LUMO energy gap (ΔE) values indicated that 1 has higher NLO activity than 2. The electronic spectra of these complexes are calculated using the TD-DFT calculations. The calculated 1H NMR chemical shift values using GIAO approach showed good correlations with the experimental data. The interaction energies using the second order perturbation theory have been used to study the different intramolecular charge transfer interactions in the studied complexes. The NBO calculations indicated that both the Agsbnd O bonds are almost identical in 2 but not in 1.

DFT predictions, synthesis, stoichiometric structures and anti-diabetic activity of Cu (II) and Fe (III) complexes of quercetin, morin, and primuletin

NASA Astrophysics Data System (ADS)

Jabeen, Erum; Janjua, Naveed Kausar; Ahmed, Safeer; Murtaza, Iram; Ali, Tahir; Masood, Nosheen; Rizvi, Aysha Sarfraz; Murtaza, Gulam

2017-12-01

The current study is aimed at the synthesis of Cu (II) and Fe (III) complexes of three flavonoids {morin (mor), quercetin (quer) and primuletin (prim)} and characterization through UV-Vis spectroscopy, cyclic voltammetry, FTIR, and thermal analysis. Structure prediction through DFT calculation was supported by experimental data. Benesi-Hildebrand equation was modified to function for 1:2 Cu-flavonoid and 1:3 Fe-flavonoid complexes. DFT predictions revealed that out of poly chelation sites present in morin and quercetin, 3-OH site was utilized as preferable chelation site while primuletin chelated through 5-OH position. In-vivo trials revealed the complexes to have better anti-diabetic potential than respective flavonoid. Fls/M-Fls proved as antagonistic to Alloxan induced diabetes and also retained anti-diabetic activity even in the presence of (2-hydroxypropyl)-β-cyclodextrin (HPβCD).

Density-functional approaches to noncovalent interactions: a comparison of dispersion corrections (DFT-D), exchange-hole dipole moment (XDM) theory, and specialized functionals.

PubMed

Burns, Lori A; Vázquez-Mayagoitia, Alvaro; Sumpter, Bobby G; Sherrill, C David

2011-02-28

A systematic study of techniques for treating noncovalent interactions within the computationally efficient density functional theory (DFT) framework is presented through comparison to benchmark-quality evaluations of binding strength compiled for molecular complexes of diverse size and nature. In particular, the efficacy of functionals deliberately crafted to encompass long-range forces, a posteriori DFT+dispersion corrections (DFT-D2 and DFT-D3), and exchange-hole dipole moment (XDM) theory is assessed against a large collection (469 energy points) of reference interaction energies at the CCSD(T) level of theory extrapolated to the estimated complete basis set limit. The established S22 [revised in J. Chem. Phys. 132, 144104 (2010)] and JSCH test sets of minimum-energy structures, as well as collections of dispersion-bound (NBC10) and hydrogen-bonded (HBC6) dissociation curves and a pairwise decomposition of a protein-ligand reaction site (HSG), comprise the chemical systems for this work. From evaluations of accuracy, consistency, and efficiency for PBE-D, BP86-D, B97-D, PBE0-D, B3LYP-D, B970-D, M05-2X, M06-2X, ωB97X-D, B2PLYP-D, XYG3, and B3LYP-XDM methodologies, it is concluded that distinct, often contrasting, groups of these elicit the best performance within the accessible double-ζ or robust triple-ζ basis set regimes and among hydrogen-bonded or dispersion-dominated complexes. For overall results, M05-2X, B97-D3, and B970-D2 yield superior values in conjunction with aug-cc-pVDZ, for a mean absolute deviation of 0.41 - 0.49 kcal/mol, and B3LYP-D3, B97-D3, ωB97X-D, and B2PLYP-D3 dominate with aug-cc-pVTZ, affording, together with XYG3/6-311+G(3df,2p), a mean absolute deviation of 0.33 - 0.38 kcal/mol.

Ammonia IRMS-TPD measurements and DFT calculation on acidic hydroxyl groups in CHA-type zeolites.

PubMed

Suzuki, Katsuki; Sastre, German; Katada, Naonobu; Niwa, Miki

2007-12-07

Brønsted acidity of H-chabazite (CHA) zeolites (Si : Al(2) = 4.2) was investigated by means of ammonia infrared-mass spectrometry/temperature-programmed desorption (IRMS-TPD) methods and density functional calculations. Four IR bands were observed at 3644, 3616, 3575 and 3538 cm(-1), and they were ascribable to the acidic OH groups on four nonequivalent oxygen sites in the CHA structure. The absorption band at 3538 cm(-1) was attributed to the O(4)H in the 6-membered ring (MR), and ammonia adsorption energy (DeltaU) of this OH group was the lowest among the 4 kinds of OH groups. The other 3 bands were assigned to the acidic OH groups in 8MR. It was observed that the DeltaU in 8 and 6MR were 131 (+/-3) and 101 kJ mol(-1), respectively. On the other hand, the density functional theory (DFT) calculations within periodic boundary conditions yielded the adsorption energies on these OH groups in 8 and 6MR to be ca. 130 and 110 kJ mol(-1), respectively, in good agreement with the experimentally-observed values.