Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

DOE PAGES

Tao, Jianmin; Ye, Lin -Hui; Duan, Yuhua

2017-11-20

The primary goal of Kohn–Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao–Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew–Burke–Ernzerhof (PBE), Tao–Perdew–Staroverov–Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree–Fock density yields the exchange and correlation energies in good agreement with the Optimizedmore » Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Lastly, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.« less

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

NASA Astrophysics Data System (ADS)

Tao, Jianmin; Ye, Lin-Hui; Duan, Yuhua

2017-12-01

The primary goal of Kohn-Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao-Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew-Burke-Ernzerhof (PBE), Tao-Perdew-Staroverov-Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree-Fock density yields the exchange and correlation energies in good agreement with the Optimized Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Finally, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

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

Tao, Jianmin; Ye, Lin -Hui; Duan, Yuhua

The primary goal of Kohn–Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao–Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew–Burke–Ernzerhof (PBE), Tao–Perdew–Staroverov–Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree–Fock density yields the exchange and correlation energies in good agreement with the Optimizedmore » Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Lastly, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.« less

Accelerating large scale Kohn-Sham density functional theory calculations with semi-local functionals and hybrid functionals

NASA Astrophysics Data System (ADS)

Lin, Lin

The computational cost of standard Kohn-Sham density functional theory (KSDFT) calculations scale cubically with respect to the system size, which limits its use in large scale applications. In recent years, we have developed an alternative procedure called the pole expansion and selected inversion (PEXSI) method. The PEXSI method solves KSDFT without solving any eigenvalue and eigenvector, and directly evaluates physical quantities including electron density, energy, atomic force, density of states, and local density of states. The overall algorithm scales as at most quadratically for all materials including insulators, semiconductors and the difficult metallic systems. The PEXSI method can be efficiently parallelized over 10,000 - 100,000 processors on high performance machines. The PEXSI method has been integrated into a number of community electronic structure software packages such as ATK, BigDFT, CP2K, DGDFT, FHI-aims and SIESTA, and has been used in a number of applications with 2D materials beyond 10,000 atoms. The PEXSI method works for LDA, GGA and meta-GGA functionals. The mathematical structure for hybrid functional KSDFT calculations is significantly different. I will also discuss recent progress on using adaptive compressed exchange method for accelerating hybrid functional calculations. DOE SciDAC Program, DOE CAMERA Program, LBNL LDRD, Sloan Fellowship.

Present, future of automotive hybrid IC applications discussed

NASA Astrophysics Data System (ADS)

Matsuda, Nobuyoshi; Fukuoka, Atuhisa

1987-09-01

Hybrid ICs are presently utilized in various fields such as commercial televisions, VTRs, and audio devices, industrial usage of communication equipment, computers, terminals, and automobiles. Its applications and environments are various and diverse. The functions required for hybrid ICs vary from simple high density mounting for a system to the realization of high mechanisms with the application of function timing. The functions are properly used depending upon the system with its hybrid ICs and its circuit composition. Considering structure and reliability requirements for automotive hybrid ICs, an application example for hybrid ICs which use the package (COMPACT), will be discussed.

From The Cover: The X3LYP extended density functional for accurate descriptions of nonbond interactions, spin states, and thermochemical properties.

PubMed

Xu, Xin; Goddard, William A

2004-03-02

We derive the form for an exact exchange energy density for a density decaying with Gaussian-like behavior at long range. Based on this, we develop the X3LYP (extended hybrid functional combined with Lee-Yang-Parr correlation functional) extended functional for density functional theory to significantly improve the accuracy for hydrogen-bonded and van der Waals complexes while also improving the accuracy in heats of formation, ionization potentials, electron affinities, and total atomic energies [over the most popular and accurate method, B3LYP (Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional)]. X3LYP also leads to a good description of dipole moments, polarizabilities, and accurate excitation energies from s to d orbitals for transition metal atoms and ions. We suggest that X3LYP will be useful for predicting ligand binding in proteins and DNA.

From The Cover: The X3LYP extended density functional for accurate descriptions of nonbond interactions, spin states, and thermochemical properties

NASA Astrophysics Data System (ADS)

Xu, Xin; Goddard, William A., III

2004-03-01

We derive the form for an exact exchange energy density for a density decaying with Gaussian-like behavior at long range. Based on this, we develop the X3LYP (extended hybrid functional combined with Lee-Yang-Parr correlation functional) extended functional for density functional theory to significantly improve the accuracy for hydrogen-bonded and van der Waals complexes while also improving the accuracy in heats of formation, ionization potentials, electron affinities, and total atomic energies [over the most popular and accurate method, B3LYP (Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional)]. X3LYP also leads to a good description of dipole moments, polarizabilities, and accurate excitation energies from s to d orbitals for transition metal atoms and ions. We suggest that X3LYP will be useful for predicting ligand binding in proteins and DNA.

The X3LYP extended density functional for accurate descriptions of nonbond interactions, spin states, and thermochemical properties

PubMed Central

Xu, Xin; Goddard, William A.

2004-01-01

We derive the form for an exact exchange energy density for a density decaying with Gaussian-like behavior at long range. Based on this, we develop the X3LYP (extended hybrid functional combined with Lee–Yang–Parr correlation functional) extended functional for density functional theory to significantly improve the accuracy for hydrogen-bonded and van der Waals complexes while also improving the accuracy in heats of formation, ionization potentials, electron affinities, and total atomic energies [over the most popular and accurate method, B3LYP (Becke three-parameter hybrid functional combined with Lee–Yang–Parr correlation functional)]. X3LYP also leads to a good description of dipole moments, polarizabilities, and accurate excitation energies from s to d orbitals for transition metal atoms and ions. We suggest that X3LYP will be useful for predicting ligand binding in proteins and DNA. PMID:14981235

Two-component hybrid time-dependent density functional theory within the Tamm-Dancoff approximation.

PubMed

Kühn, Michael; Weigend, Florian

2015-01-21

We report the implementation of a two-component variant of time-dependent density functional theory (TDDFT) for hybrid functionals that accounts for spin-orbit effects within the Tamm-Dancoff approximation (TDA) for closed-shell systems. The influence of the admixture of Hartree-Fock exchange on excitation energies is investigated for several atoms and diatomic molecules by comparison to numbers for pure density functionals obtained previously [M. Kühn and F. Weigend, J. Chem. Theory Comput. 9, 5341 (2013)]. It is further related to changes upon switching to the local density approximation or using the full TDDFT formalism instead of TDA. Efficiency is demonstrated for a comparably large system, Ir(ppy)3 (61 atoms, 1501 basis functions, lowest 10 excited states), which is a prototype molecule for organic light-emitting diodes, due to its "spin-forbidden" triplet-singlet transition.

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

Song, Jong-Won; Hirao, Kimihiko, E-mail: hirao@riken.jp

Since the advent of hybrid functional in 1993, it has become a main quantum chemical tool for the calculation of energies and properties of molecular systems. Following the introduction of long-range corrected hybrid scheme for density functional theory a decade later, the applicability of the hybrid functional has been further amplified due to the resulting increased performance on orbital energy, excitation energy, non-linear optical property, barrier height, and so on. Nevertheless, the high cost associated with the evaluation of Hartree-Fock (HF) exchange integrals remains a bottleneck for the broader and more active applications of hybrid functionals to large molecular andmore » periodic systems. Here, we propose a very simple yet efficient method for the computation of long-range corrected hybrid scheme. It uses a modified two-Gaussian attenuating operator instead of the error function for the long-range HF exchange integral. As a result, the two-Gaussian HF operator, which mimics the shape of the error function operator, reduces computational time dramatically (e.g., about 14 times acceleration in C diamond calculation using periodic boundary condition) and enables lower scaling with system size, while maintaining the improved features of the long-range corrected density functional theory.« less

A long-range-corrected density functional that performs well for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states.

PubMed

Rohrdanz, Mary A; Martins, Katie M; Herbert, John M

2009-02-07

We introduce a hybrid density functional that asymptotically incorporates full Hartree-Fock exchange, based on the long-range-corrected exchange-hole model of Henderson et al. [J. Chem. Phys. 128, 194105 (2008)]. The performance of this functional, for ground-state properties and for vertical excitation energies within time-dependent density functional theory, is systematically evaluated, and optimal values are determined for the range-separation parameter, omega, and for the fraction of short-range Hartree-Fock exchange. We denote the new functional as LRC-omegaPBEh, since it reduces to the standard PBEh hybrid functional (also known as PBE0 or PBE1PBE) for a certain choice of its two parameters. Upon optimization of these parameters against a set of ground- and excited-state benchmarks, the LRC-omegaPBEh functional fulfills three important requirements: (i) It outperforms the PBEh hybrid functional for ground-state atomization energies and reaction barrier heights; (ii) it yields statistical errors comparable to PBEh for valence excitation energies in both small and medium-sized molecules; and (iii) its performance for charge-transfer excitations is comparable to its performance for valence excitations. LRC-omegaPBEh, with the parameters determined herein, is the first density functional that satisfies all three criteria. Notably, short-range Hartree-Fock exchange appears to be necessary in order to obtain accurate ground-state properties and vertical excitation energies using the same value of omega.

Critical Role of the Exchange Interaction for the Electronic Structure and Charge-Density-Wave Formation in TiSe2

NASA Astrophysics Data System (ADS)

Hellgren, Maria; Baima, Jacopo; Bianco, Raffaello; Calandra, Matteo; Mauri, Francesco; Wirtz, Ludger

2017-10-01

We show that the inclusion of screened exchange via hybrid functionals provides a unified description of the electronic and vibrational properties of TiSe2 . In contrast to local approximations in density functional theory, the explicit inclusion of exact, nonlocal exchange captures the effects of the electron-electron interaction needed to both separate the Ti -d states from the Se -p states and stabilize the charge-density-wave (CDW) (or low-T ) phase through the formation of a p -d hybridized state. We further show that this leads to an enhanced electron-phonon coupling that can drive the transition even if a small gap opens in the high-T phase. Finally, we demonstrate that the hybrid functionals can generate a CDW phase where the electronic bands, the geometry, and the phonon frequencies are in agreement with experiments.

Optimization of a hybrid exchange-correlation functional for silicon carbides

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

Oda, Takuji; Zhang, Yanwen; Weber, William J

2013-01-01

A hybrid exchange-correlation functional is optimized in order to accurately describe the nature of silicon carbides (SiC) in the framework of ab-initio calculations based on density functional theory (DFT), especially with an aim toward future applications in defect studies. It is shown that the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional with the screening parameter of 0.15 -1 outperforms conventional exchange-correlation functionals and other popular hybrid functionals regarding description of band structures in SiC. High transferability is proven through assessment over various SiC polytypes, silicon and diamond. Excellent performance is also confirmed for other fundamental material properties including elastic constants and phonon frequency.

Synthesis and characterization of transition metal oxide/sulfide nanostructures for electrochemical applications

NASA Astrophysics Data System (ADS)

Yilmaz, Gamze

This thesis is essentially oriented to develop low-cost nanostructured transition metal (nickel and vanadium) oxides and sulfides with high energy density, power density and electrochemical stability via strategies of structural design, hybridization, functionalization and surface engineering. Metal oxide and metal oxide/sulfide hybrid nanostructures in several designs, including hierarchical porous nanostructures, hollow polyhedrons, nanocubes, nanoframes, octopod nanoframes, and nanocages, were synthesized to study the contribution of structural design, compositional engineering, functionalization and surface engineering to the electrochemical properties of the materials. Modulated compositional and structural features disclosed the opportunities of large accessible active sites, facile ion transport, robustness and enhanced electrical conductivity. The best electrochemical performance with merits of highest energy density (38.9 Wh kg-1), power density (7.4 kW kg-1) and electrochemical stability (90.9% after 10000 cycles) was obtained for nickel cobalt layered double hydroxide/cobalt sulfide (NiCo-LDH/Co9S8) hybrid hollow polyhedron structure.

Hybrid Density Functional Study of the Local Structures and Energy Levels of CaAl2O4:Ce3.

PubMed

Lou, Bibo; Jing, Weiguo; Lou, Liren; Zhang, Yongfan; Yin, Min; Duan, Chang-Kui

2018-05-03

First-principles calculations were carried out for the electronic structures of Ce 3+ in calcium aluminate phosphors, CaAl 2 O 4 , and their effects on luminescence properties. Hybrid density functional approaches were used to overcome the well-known underestimation of band gaps of conventional density functional approaches and to calculate the energy levels of Ce 3+ ions more accurately. The obtained 4f-5d excitation and emission energies show good consistency with measured values. A detailed energy diagram of all three sites is obtained, which explains qualitatively all of the luminescent phenomena. With the results of energy levels calculated by combining the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE06) and the constraint occupancy approach, we are able to construct a configurational coordinate diagram to analyze the processes of capture of a hole or an electron and luminescence. This approach can be applied for systematic high-throughput calculations in predicting Ce 3+ activated luminescent materials with a moderate computing requirement.

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

Density functional study of double ionization energies

NASA Astrophysics Data System (ADS)

Chong, D. P.

2008-02-01

In this paper, double ionization energies (DIEs) of gas-phase atoms and molecules are calculated by energy difference method with density functional theory. To determine the best functional for double ionization energies, we first study 24 main group atoms in the second, third, and fourth periods. An approximation is used in which the electron density is first obtained from a density functional computation with the exchange-correlation potential Vxc known as statistical average of orbital potentials, after which the energy is computed from that density with 59 different exchange-correlation energy functionals Exc. For the 24 atoms, the two best Exc functional providing DIEs with average absolute deviation (AAD) of only 0.25eV are the Perdew-Burke-Ernzerhof functional modified by Hammer et al. [Phys. Rev. B 59, 6413 (1999)] and one known as the Krieger-Chen-Iafrate-Savin functional modified by Krieger et al. (unpublished). Surprisingly, none of the 20 available hybrid functionals is among the top 15 functionals for the DIEs of the 24 atoms. A similar procedure is then applied to molecules, with opposite results: Only hybrid functionals are among the top 15 functionals for a selection of 29molecules. The best Exc functional for the 29molecules is found to be the Becke 1997 functional modified by Wilson et al. [J. Chem. Phys. 115, 9233 (2001)]. With that functional, the AAD from experiment for DIEs of 29molecules is just under 0.5eV. If the two suspected values for C2H2 and Fe(CO)5 are excluded, the AAD improves to 0.32eV. Many other hybrid functionals perform almost as well.

Density functional with full exact exchange, balanced nonlocality of correlations, and constraint satisfaction

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

Tao, Jianmin; Perdew, John P; Staroverov, Viktor N

2008-01-01

We construct a nonlocal density functional approximation with full exact exchange, while preserving the constraint-satisfaction approach and justified error cancellations of simpler semilocal functionals. This is achieved by interpolating between different approximations suitable for two extreme regions of the electron density. In a 'normal' region, the exact exchange-correlation hole density around an electron is semilocal because its spatial range is reduced by correlation and because it integrates over a narrow range to -1. These regions are well described by popular semilocal approximations (many of which have been constructed nonempirically), because of proper accuracy for a slowly-varying density or because ofmore » error cancellation between exchange and correlation. 'Abnormal' regions, where non locality is unveiled, include those in which exchange can dominate correlation (one-electron, nonuniform high-density, and rapidly-varying limits), and those open subsystems of fluctuating electron number over which the exact exchange-correlation hole integrates to a value greater than -1. Regions between these extremes are described by a hybrid functional mixing exact and semi local exchange energy densities locally (i.e., with a mixing fraction that is a function of position r and a functional of the density). Because our mixing fraction tends to 1 in the high-density limit, we employ full exact exchange according to the rigorous definition of the exchange component of any exchange-correlation energy functional. Use of full exact exchange permits the satisfaction of many exact constraints, but the nonlocality of exchange also requires balanced nonlocality of correlation. We find that this nonlocality can demand at least five empirical parameters (corresponding roughly to the four kinds of abnormal regions). Our local hybrid functional is perhaps the first accurate size-consistent density functional with full exact exchange. It satisfies other known exact constraints, including exactness for all one-electron densities, and provides an excellent, fit 1.0 the 223 molecular enthalpies of formation of the G3/99 set and the 42 reaction barrier heights of the BH42/03 set, improving both (but especially the latter) over most semilocal functionals and global hybrids. Exact constraints, physical insights, and paradigm examples hopefully suppress 'overfitting'.« less

Functionalization of poly(methyl methacrylate) (PMMA) as a substrate for DNA microarrays

PubMed Central

Fixe, F.; Dufva, M.; Telleman, P.; Christensen, C. B. V.

2004-01-01

A chemical procedure was developed to functionalize poly(methyl methacrylate) (PMMA) substrates. PMMA is reacted with hexamethylene diamine to yield an aminated surface for immobilizing DNA in microarrays. The density of primary NH2 groups was 0.29 nmol/cm2. The availability of these primary amines was confirmed by the immobilization of DNA probes and hybridization with a complementary DNA strand. The hybridization signal and the hybridization efficiency of the chemically aminated PMMA slides were comparable to the hybridization signal and the hybridization efficiency obtained from differently chemically modified PMMA slides, silanized glass, commercial silylated glass and commercial plastic Euray™ slides. Immobilized and hybridized densities of 10 and 0.75 pmol/cm2, respectively, were observed for microarrays on chemically aminated PMMA. The immobilized probes were heat stable since the hybridization performance of microarrays subjected to 20 PCR heat cycles was only reduced by 4%. In conclusion, this new strategy to modify PMMA provides a robust procedure to immobilize DNA, which is a very useful substrate for fabricating single use diagnostics devices with integrated functions, like sample preparation, treatment and detection using microfabrication and microelectronic techniques. PMID:14718554

Survival of the most transferable at the top of Jacob's ladder: Defining and testing the ωB97M(2) double hybrid density functional

NASA Astrophysics Data System (ADS)

Mardirossian, Narbe; Head-Gordon, Martin

2018-06-01

A meta-generalized gradient approximation, range-separated double hybrid (DH) density functional with VV10 non-local correlation is presented. The final 14-parameter functional form is determined by screening trillions of candidate fits through a combination of best subset selection, forward stepwise selection, and random sample consensus (RANSAC) outlier detection. The MGCDB84 database of 4986 data points is employed in this work, containing a training set of 870 data points, a validation set of 2964 data points, and a test set of 1152 data points. Following an xDH approach, orbitals from the ωB97M-V density functional are used to compute the second-order perturbation theory correction. The resulting functional, ωB97M(2), is benchmarked against a variety of leading double hybrid density functionals, including B2PLYP-D3(BJ), B2GPPLYP-D3(BJ), ωB97X-2(TQZ), XYG3, PTPSS-D3(0), XYGJ-OS, DSD-PBEP86-D3(BJ), and DSD-PBEPBE-D3(BJ). Encouragingly, the overall performance of ωB97M(2) on nearly 5000 data points clearly surpasses that of all of the tested density functionals. As a Rung 5 density functional, ωB97M(2) completes our family of combinatorially optimized functionals, complementing B97M-V on Rung 3, and ωB97X-V and ωB97M-V on Rung 4. The results suggest that ωB97M(2) has the potential to serve as a powerful predictive tool for accurate and efficient electronic structure calculations of main-group chemistry.

Structural and electronic properties of U{sub n}O{sub m} (n=1-3,m=1-3n) clusters: A theoretical study using screened hybrid density functional theory

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

Yang, Yu; Liu, Haitao; Zhang, Ping, E-mail: zhang-ping@iapcm.ac.cn

The structural and electronic properties of small uranium oxide clusters U{sub n}O{sub m} (n=1-3, m=1-3n) are systematically studied within the screened hybrid density functional theory. It is found that the formation of U–O–U bondings and isolated U–O bonds are energetically more stable than U–U bondings. As a result, no uranium cores are observed. Through fragmentation studies, we find that the U{sub n}O{sub m} clusters with the m/n ratio between 2 and 2.5 are very stable, hinting that UO{sub 2+x} hyperoxides are energetically stable. Electronically, we find that the O-2p states always distribute in the deep energy range, and the U-5fmore » states always distribute at the two sides of the Fermi level. The U-6d states mainly hybridize with the U-5f states in U-rich clusters, while hybridizing with O-2p states in O-rich clusters. Our work is the first one on the screened hybrid density functional theory level studying the atomic and electronic properties of the actinide oxide clusters.« less

Hybrid density-functional calculations of phonons in LaCoO3

NASA Astrophysics Data System (ADS)

Gryaznov, Denis; Evarestov, Robert A.; Maier, Joachim

2010-12-01

Phonon frequencies at Γ point in nonmagnetic rhombohedral phase of LaCoO3 were calculated using density-functional theory with hybrid exchange correlation functional PBE0. The calculations involved a comparison of results for two types of basis functions commonly used in ab initio calculations, namely, the plane-wave approach and linear combination of atomic orbitals, as implemented in VASP and CRYSTAL computer codes, respectively. A good qualitative, but also within an error margin of less than 30%, a quantitative agreement was observed not only between the two formalisms but also between theoretical and experimental phonon frequency predictions. Moreover, the correlation between the phonon symmetries in cubic and rhombohedral phases is discussed in detail on the basis of group-theoretical analysis. It is concluded that the hybrid PBE0 functional is able to predict correctly the phonon properties in LaCoO3 .

Doping Level of Boron-Doped Diamond Electrodes Controls the Grafting Density of Functional Groups for DNA Assays.

PubMed

Švorc, Ĺubomír; Jambrec, Daliborka; Vojs, Marian; Barwe, Stefan; Clausmeyer, Jan; Michniak, Pavol; Marton, Marián; Schuhmann, Wolfgang

2015-09-02

The impact of different doping levels of boron-doped diamond on the surface functionalization was investigated by means of electrochemical reduction of aryldiazonium salts. The grafting efficiency of 4-nitrophenyl groups increased with the boron levels (B/C ratio from 0 to 20,000 ppm). Controlled grafting of nitrophenyldiazonium was used to adjust the amount of immobilized single-stranded DNA strands at the surface and further on the hybridization yield in dependence on the boron doping level. The grafted nitro functions were electrochemically reduced to the amine moieties. Subsequent functionalization with a succinic acid introduced carboxyl groups for subsequent binding of an amino-terminated DNA probe. DNA hybridization significantly depends on the probe density which is in turn dependent on the boron doping level. The proposed approach opens new insights for the design and control of doped diamond surface functionalization for the construction of DNA hybridization assays.

Density Functional Theory and Beyond for Band-Gap Screening: Performance for Transition-Metal Oxides and Dichalcogenides.

PubMed

Li, Wenqing; Walther, Christian F J; Kuc, Agnieszka; Heine, Thomas

2013-07-09

The performance of a wide variety of commonly used density functionals, as well as two screened hybrid functionals (HSE06 and TB-mBJ), on predicting electronic structures of a large class of en vogue materials, such as metal oxides, chalcogenides, and nitrides, is discussed in terms of band gaps, band structures, and projected electronic densities of states. Contrary to GGA, hybrid functionals and GGA+U, both HSE06 and TB-mBJ are able to predict band gaps with an appreciable accuracy of 25% and thus allow the screening of various classes of transition-metal-based compounds, i.e., mixed or doped materials, at modest computational cost. The calculated electronic structures are largely unaffected by the choice of basis functions and software implementation, however, might be subject to the treatment of the core electrons.

An open-source framework for analyzing N-electron dynamics. II. Hybrid density functional theory/configuration interaction methodology.

PubMed

Hermann, Gunter; Pohl, Vincent; Tremblay, Jean Christophe

2017-10-30

In this contribution, we extend our framework for analyzing and visualizing correlated many-electron dynamics to non-variational, highly scalable electronic structure method. Specifically, an explicitly time-dependent electronic wave packet is written as a linear combination of N-electron wave functions at the configuration interaction singles (CIS) level, which are obtained from a reference time-dependent density functional theory (TDDFT) calculation. The procedure is implemented in the open-source Python program detCI@ORBKIT, which extends the capabilities of our recently published post-processing toolbox (Hermann et al., J. Comput. Chem. 2016, 37, 1511). From the output of standard quantum chemistry packages using atom-centered Gaussian-type basis functions, the framework exploits the multideterminental structure of the hybrid TDDFT/CIS wave packet to compute fundamental one-electron quantities such as difference electronic densities, transient electronic flux densities, and transition dipole moments. The hybrid scheme is benchmarked against wave function data for the laser-driven state selective excitation in LiH. It is shown that all features of the electron dynamics are in good quantitative agreement with the higher-level method provided a judicious choice of functional is made. Broadband excitation of a medium-sized organic chromophore further demonstrates the scalability of the method. In addition, the time-dependent flux densities unravel the mechanistic details of the simulated charge migration process at a glance. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

A hybrid density functional study of silicon and phosphorus doped hexagonal boron nitride monolayer

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Igumbor, E.; Chetty, N.

2016-10-01

We present a hybrid density functional study of silicon (Si) and phosphorus (P) doped hexagonal boron nitride (h-BN). The local geometry, electronic structure and thermodynamic stability of Si B , Si N , P B and P N are examined using hybrid Heyd-Scuseria- Ernzerhof (HSE) functional. The defect induced buckling and the local bond distances around the defect are sensitive to charge state modulation q = -2, -1, 0, +1 and +2. The +1 charge state is found to be the most energetically stable state and significantly reduces the buckling. Based on the charge state thermodynamic transition levels, we noted that the Si N , Si N and P B defects are too deep to be ionized, and can alter the optical properties of h-BN material.

Electron transport in polycyclic aromatic hydrocarbons/boron nitride hybrid structures: density functional theory combined with the nonequilibrium Green's function.

PubMed

Panahi, S F K S; Namiranian, Afshin; Soleimani, Maryam; Jamaati, Maryam

2018-02-07

We investigate the electronic transport properties of two types of junction based on single polyaromatic hydrocarbons (PAHs) and PAHs embedded in boron nitride (h-BN) nanoribbons, using nonequilibrium Green's functions (NEGF) and density functional theory (DFT). In the PAH junctions, a Fano resonance line shape at the Fermi energy in the transport feature can be clearly seen. In hybrid junctions, structural asymmetries enable interactions between the electronic states, leading to observation of interface-based transport. Our findings reveal that the interface of PAH/h-BN strongly affects the transport properties of the structures.

Exploring the limit of accuracy for density functionals based on the generalized gradient approximation: Local, global hybrid, and range-separated hybrid functionals with and without dispersion corrections

DOE PAGES

Mardirossian, Narbe; Head-Gordon, Martin

2014-03-25

The limit of accuracy for semi-empirical generalized gradient approximation (GGA) density functionals is explored in this paper by parameterizing a variety of local, global hybrid, and range-separated hybrid functionals. The training methodology employed differs from conventional approaches in 2 main ways: (1) Instead of uniformly truncating the exchange, same-spin correlation, and opposite-spin correlation functional inhomogeneity correction factors, all possible fits up to fourth order are considered, and (2) Instead of selecting the optimal functionals based solely on their training set performance, the fits are validated on an independent test set and ranked based on their overall performance on the trainingmore » and test sets. The 3 different methods of accounting for exchange are trained both with and without dispersion corrections (DFT-D2 and VV10), resulting in a total of 491 508 candidate functionals. For each of the 9 functional classes considered, the results illustrate the trade-off between improved training set performance and diminished transferability. Since all 491 508 functionals are uniformly trained and tested, this methodology allows the relative strengths of each type of functional to be consistently compared and contrasted. Finally, the range-separated hybrid GGA functional paired with the VV10 nonlocal correlation functional emerges as the most accurate form for the present training and test sets, which span thermochemical energy differences, reaction barriers, and intermolecular interactions involving lighter main group elements.« less

A hybrid pareto mixture for conditional asymmetric fat-tailed distributions.

PubMed

Carreau, Julie; Bengio, Yoshua

2009-07-01

In many cases, we observe some variables X that contain predictive information over a scalar variable of interest Y , with (X,Y) pairs observed in a training set. We can take advantage of this information to estimate the conditional density p(Y|X = x). In this paper, we propose a conditional mixture model with hybrid Pareto components to estimate p(Y|X = x). The hybrid Pareto is a Gaussian whose upper tail has been replaced by a generalized Pareto tail. A third parameter, in addition to the location and spread parameters of the Gaussian, controls the heaviness of the upper tail. Using the hybrid Pareto in a mixture model results in a nonparametric estimator that can adapt to multimodality, asymmetry, and heavy tails. A conditional density estimator is built by modeling the parameters of the mixture estimator as functions of X. We use a neural network to implement these functions. Such conditional density estimators have important applications in many domains such as finance and insurance. We show experimentally that this novel approach better models the conditional density in terms of likelihood, compared to competing algorithms: conditional mixture models with other types of components and a classical kernel-based nonparametric model.

Self-consistent hybrid functionals for solids: a fully-automated implementation

NASA Astrophysics Data System (ADS)

Erba, A.

2017-08-01

A fully-automated algorithm for the determination of the system-specific optimal fraction of exact exchange in self-consistent hybrid functionals of the density-functional-theory is illustrated, as implemented into the public Crystal program. The exchange fraction of this new class of functionals is self-consistently updated proportionally to the inverse of the dielectric response of the system within an iterative procedure (Skone et al 2014 Phys. Rev. B 89, 195112). Each iteration of the present scheme, in turn, implies convergence of a self-consistent-field (SCF) and a coupled-perturbed-Hartree-Fock/Kohn-Sham (CPHF/KS) procedure. The present implementation, beside improving the user-friendliness of self-consistent hybrids, exploits the unperturbed and electric-field perturbed density matrices from previous iterations as guesses for subsequent SCF and CPHF/KS iterations, which is documented to reduce the overall computational cost of the whole process by a factor of 2.

Enhanced NMR Discrimination of Pharmaceutically Relevant Molecular Crystal Forms through Fragment-Based Ab Initio Chemical Shift Predictions.

PubMed

Hartman, Joshua D; Day, Graeme M; Beran, Gregory J O

2016-11-02

Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction. Fragment methods allow hybrid density functionals to be employed routinely in chemical shift prediction, and we have recently demonstrated appreciable improvements in the accuracy of the predicted shifts when using the hybrid PBE0 functional instead of generalized gradient approximation (GGA) functionals like PBE. Here, we investigate the solid-state 13 C and 15 N NMR spectra for multiple crystal forms of acetaminophen, phenobarbital, and testosterone. We demonstrate that the use of the hybrid density functional instead of a GGA provides both higher accuracy in the chemical shifts and increased discrimination among the different crystallographic environments. Finally, these results also provide compelling evidence for the transferability of the linear regression parameters mapping predicted chemical shieldings to chemical shifts that were derived in an earlier study.

Enhanced NMR Discrimination of Pharmaceutically Relevant Molecular Crystal Forms through Fragment-Based Ab Initio Chemical Shift Predictions

PubMed Central

2016-01-01

Chemical shift prediction plays an important role in the determination or validation of crystal structures with solid-state nuclear magnetic resonance (NMR) spectroscopy. One of the fundamental theoretical challenges lies in discriminating variations in chemical shifts resulting from different crystallographic environments. Fragment-based electronic structure methods provide an alternative to the widely used plane wave gauge-including projector augmented wave (GIPAW) density functional technique for chemical shift prediction. Fragment methods allow hybrid density functionals to be employed routinely in chemical shift prediction, and we have recently demonstrated appreciable improvements in the accuracy of the predicted shifts when using the hybrid PBE0 functional instead of generalized gradient approximation (GGA) functionals like PBE. Here, we investigate the solid-state 13C and 15N NMR spectra for multiple crystal forms of acetaminophen, phenobarbital, and testosterone. We demonstrate that the use of the hybrid density functional instead of a GGA provides both higher accuracy in the chemical shifts and increased discrimination among the different crystallographic environments. Finally, these results also provide compelling evidence for the transferability of the linear regression parameters mapping predicted chemical shieldings to chemical shifts that were derived in an earlier study. PMID:27829821

Affordable and accurate large-scale hybrid-functional calculations on GPU-accelerated supercomputers

NASA Astrophysics Data System (ADS)

Ratcliff, Laura E.; Degomme, A.; Flores-Livas, José A.; Goedecker, Stefan; Genovese, Luigi

2018-03-01

Performing high accuracy hybrid functional calculations for condensed matter systems containing a large number of atoms is at present computationally very demanding or even out of reach if high quality basis sets are used. We present a highly optimized multiple graphics processing unit implementation of the exact exchange operator which allows one to perform fast hybrid functional density-functional theory (DFT) calculations with systematic basis sets without additional approximations for up to a thousand atoms. With this method hybrid DFT calculations of high quality become accessible on state-of-the-art supercomputers within a time-to-solution that is of the same order of magnitude as traditional semilocal-GGA functionals. The method is implemented in a portable open-source library.

ωB97M-V: A combinatorially optimized, range-separated hybrid, meta-GGA density functional with VV10 nonlocal correlation

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

Mardirossian, Narbe; Head-Gordon, Martin

2016-06-07

A combinatorially optimized, range-separated hybrid, meta-GGA density functional with VV10 nonlocal correlation is presented in this paper. The final 12-parameter functional form is selected from approximately 10 × 10 9 candidate fits that are trained on a training set of 870 data points and tested on a primary test set of 2964 data points. The resulting density functional, ωB97M-V, is further tested for transferability on a secondary test set of 1152 data points. For comparison, ωB97M-V is benchmarked against 11 leading density functionals including M06-2X, ωB97X-D, M08-HX, M11, ωM05-D, ωB97X-V, and MN15. Encouragingly, the overall performance of ωB97M-V on nearlymore » 5000 data points clearly surpasses that of all of the tested density functionals. Finally, in order to facilitate the use of ωB97M-V, its basis set dependence and integration grid sensitivity are thoroughly assessed, and recommendations that take into account both efficiency and accuracy are provided.« less

An efficient method for hybrid density functional calculation with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Wang, Maoyuan; Liu, Gui-Bin; Guo, Hong; Yao, Yugui

2018-03-01

In first-principles calculations, hybrid functional is often used to improve accuracy from local exchange correlation functionals. A drawback is that evaluating the hybrid functional needs significantly more computing effort. When spin-orbit coupling (SOC) is taken into account, the non-collinear spin structure increases computing effort by at least eight times. As a result, hybrid functional calculations with SOC are intractable in most cases. In this paper, we present an approximate solution to this problem by developing an efficient method based on a mixed linear combination of atomic orbital (LCAO) scheme. We demonstrate the power of this method using several examples and we show that the results compare very well with those of direct hybrid functional calculations with SOC, yet the method only requires a computing effort similar to that without SOC. The presented technique provides a good balance between computing efficiency and accuracy, and it can be extended to magnetic materials.

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

Lee, Hyewon; Cheong, S.W.; Kim, Bog G., E-mail: boggikim@pusan.ac.kr

We have studied the properties of SnO{sub 6} octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO{sub 6} containing perovskites. We also have expended the hybrid density functional calculation to the ASnO{sub 3}/A'SnO{sub 3} system with different cation orderings. We propose an empirical relationshipmore » between the tolerance factor and the band gap of SnO{sub 6} containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO{sub 3} for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO{sub 6} octahedrons are plotted as polyhedron. (b) Band gap of ASnO{sub 3} as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO{sub 3}/A'SnO{sub 3} superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO{sub 3}, [001] ordered superlattices, and [111] ordered superlattices of ASnO{sub 3}/A'SnO{sub 3} as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO{sub 3} and ASnO{sub 3}/A'SnO{sub 3}. • The band gap of ASnO{sub 3} using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap.« less

Importance of the Kinetic Energy Density for Band Gap Calculations in Solids with Density Functional Theory.

PubMed

Tran, Fabien; Blaha, Peter

2017-05-04

Recently, exchange-correlation potentials in density functional theory were developed with the goal of providing improved band gaps in solids. Among them, the semilocal potentials are particularly interesting for large systems since they lead to calculations that are much faster than with hybrid functionals or methods like GW. We present an exhaustive comparison of semilocal exchange-correlation potentials for band gap calculations on a large test set of solids, and particular attention is paid to the potential HLE16 proposed by Verma and Truhlar. It is shown that the most accurate potential is the modified Becke-Johnson potential, which, most noticeably, is much more accurate than all other semilocal potentials for strongly correlated systems. This can be attributed to its additional dependence on the kinetic energy density. It is also shown that the modified Becke-Johnson potential is at least as accurate as the hybrid functionals and more reliable for solids with large band gaps.

Transitioning NWChem to the Next Generation of Manycore Machines

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

Bylaska, Eric J.; Apra, E; Kowalski, Karol

The NorthWest chemistry (NWChem) modeling software is a popular molecular chemistry simulation software that was designed from the start to work on massively parallel processing supercomputers [1-3]. It contains an umbrella of modules that today includes self-consistent eld (SCF), second order Møller-Plesset perturbation theory (MP2), coupled cluster (CC), multiconguration self-consistent eld (MCSCF), selected conguration interaction (CI), tensor contraction engine (TCE) many body methods, density functional theory (DFT), time-dependent density functional theory (TDDFT), real-time time-dependent density functional theory, pseudopotential plane-wave density functional theory (PSPW), band structure (BAND), ab initio molecular dynamics (AIMD), Car-Parrinello molecular dynamics (MD), classical MD, hybrid quantum mechanicsmore » molecular mechanics (QM/MM), hybrid ab initio molecular dynamics molecular mechanics (AIMD/MM), gauge independent atomic orbital nuclear magnetic resonance (GIAO NMR), conductor like screening solvation model (COSMO), conductor-like screening solvation model based on density (COSMO-SMD), and reference interaction site model (RISM) solvation models, free energy simulations, reaction path optimization, parallel in time, among other capabilities [4]. Moreover, new capabilities continue to be added with each new release.« less

BN-C Hybrid Nanoribbons as Gas Sensors

NASA Astrophysics Data System (ADS)

Darvishi Gilan, Mahdi; Chegel, Raad

2018-02-01

The effects of carbon monoxide (CO) and ammonia (NH3) molecules adsorption on the various composites of boron nitride and graphene BN-C hybrid nanoribbons are investigated using the non-equilibrium Green's function (NEGF) technique based on density functional theory (DFT). The effects of adsorption with possible random configurations on the average of the density of states (DOS), transmission coefficient, and the current-voltage ( I- V) characteristics are calculated. The results indicate that, by embedding armchair graphene nanoribbon (AGNR) with boron nitride nanoribbon (BNNR), the various electronic properties can be observed after gas molecule adsorption. The electronic structure and gap of hybrids system is modified due to gas adsorption, and the systems act like the n-type semiconductor by NH3 molecule adsorption. The hybrid structures due to their tunable band gap are better candidates for gas detecting compared to the pristine BNNRs and AGNRs.

Recent developments in LIBXC - A comprehensive library of functionals for density functional theory

NASA Astrophysics Data System (ADS)

Lehtola, Susi; Steigemann, Conrad; Oliveira, Micael J. T.; Marques, Miguel A. L.

2018-01-01

LIBXC is a library of exchange-correlation functionals for density-functional theory. We are concerned with semi-local functionals (or the semi-local part of hybrid functionals), namely local-density approximations, generalized-gradient approximations, and meta-generalized-gradient approximations. Currently we include around 400 functionals for the exchange, correlation, and the kinetic energy, spanning more than 50 years of research. Moreover, LIBXC is by now used by more than 20 codes, not only from the atomic, molecular, and solid-state physics, but also from the quantum chemistry communities.

Hybrid density functional study of structural, bonding, and electronic properties of the manganite series La1-xCaxMnO3 (x =0,1/4,1)

NASA Astrophysics Data System (ADS)

Korotana, R.; Mallia, G.; Gercsi, Z.; Liborio, L.; Harrison, N. M.

2014-05-01

Hybrid-exchange density functional theory calculations are carried out to determine the effects of A-site doping on the electronic and magnetic properties of the manganite series La1-xCaxMnO3. This study focuses on the ground state of an ordered Ca occupancy in a periodic structure. It is shown that the hybrid-exchange functional, Becke three-parameter Lee-Yang-Parr (B3LYP), provides an accurate and consistent description of the electronic structure for LaMnO3, CaMnO3, and La0.75Ca0.25MnO3. We have quantified the relevant structural, magnetic, and electronic energy contributions to the stability of the doped compound. An insight into the exchange coupling mechanism for the low hole density region of the phase diagram, where a polaron (anti-Jahn-Teller) forms, is also provided. This study completes a microscopic description of the lightly doped insulator with an antiferromagnetic-to-ferromagnetic and metal-to-insulator transition.

Hybrid functional studies of stability and diffusion of hydrogen in Mg-doped GaN

NASA Astrophysics Data System (ADS)

Park, Ji-Sang; Chang, K. J.

2012-02-01

Nitride semiconductors are known to suffer from low p-type doping efficiency due to the high activation energy of Mg acceptors and the compensation of hole carriers. To enhance hole carrier concentration, the hydrogen co-doping method is widely used, in which hydrogen is intentionally doped with Mg dopants and removed by subsequent thermal annealing. In this work, we perform first-principles density functional calculations to study the stability and diffusion of hydrogen in Mg-doped GaN. For the exchange-correlation potential, we employ both the generalized gradient approximation (GGA) proposed by Perdew, Burke, and Ernzerhof and the hybrid density functional of Heyd, Scuseria, and Ernzerhof. We examine the diffusion pathways and dissociation barriers of H from the Mg-H complex using the nudged elastic band and dimer methods. We compare the results of the GGA and hybrid density functional calculations for the stability of various H interstitial configurations and the migration barriers for H diffusion. Finally, using the calculated migration barriers as inputs, we perform kinetic Monte Carlo simulations for the dissociation of the Mg-H complex and find that the Mg acceptors are activated by thermal annealing up to 700-800 ^oC, in good agreement with experiments.

Hybrid sp2+sp3 carbon phases created from carbon nanotubes

NASA Astrophysics Data System (ADS)

Tingaev, M. I.; Belenkov, E. A.

2017-11-01

Using the density functional theory in the gradient approximation (DFT-GGA) methods was calculated the geometrically optimized structure and electronic properties for six new hybrid carbon phases. These hybrid phases consists of atoms in three - and four-coordinated (sp2+sp3-hybridized) states. The initial structure of the carbon phases was constructed by partial cross-linking of (8,0) carbon nanotube bundles. Sublimation energies calculated for hybrid phases above the sublimation energy of cubic diamond, however, fall into the range of values typical for carbon materials, which are stable under normal conditions. The density of electronic states at the Fermi energy for the two phases is non-zero and these phases should have metallic properties. The other hybrid phases should be semiconductors with a band gap from 0.5 to 1.1 eV.

Benchmarking Density Functional Theory Based Methods To Model NiOOH Material Properties: Hubbard and van der Waals Corrections vs Hybrid Functionals.

PubMed

Zaffran, Jeremie; Caspary Toroker, Maytal

2016-08-09

NiOOH has recently been used to catalyze water oxidation by way of electrochemical water splitting. Few experimental data are available to rationalize the successful catalytic capability of NiOOH. Thus, theory has a distinctive role for studying its properties. However, the unique layered structure of NiOOH is associated with the presence of essential dispersion forces within the lattice. Hence, the choice of an appropriate exchange-correlation functional within Density Functional Theory (DFT) is not straightforward. In this work, we will show that standard DFT is sufficient to evaluate the geometry, but DFT+U and hybrid functionals are required to calculate the oxidation states. Notably, the benefit of DFT with van der Waals correction is marginal. Furthermore, only hybrid functionals succeed in opening a bandgap, and such methods are necessary to study NiOOH electronic structure. In this work, we expect to give guidelines to theoreticians dealing with this material and to present a rational approach in the choice of the DFT method of calculation.

A density spike on astrophysical scales from an N-field waterfall transition

NASA Astrophysics Data System (ADS)

Halpern, Illan F.; Hertzberg, Mark P.; Joss, Matthew A.; Sfakianakis, Evangelos I.

2015-09-01

Hybrid inflation models are especially interesting as they lead to a spike in the density power spectrum on small scales, compared to the CMB, while also satisfying current bounds on tensor modes. Here we study hybrid inflation with N waterfall fields sharing a global SO (N) symmetry. The inclusion of many waterfall fields has the obvious advantage of avoiding topologically stable defects for N > 3. We find that it also has another advantage: it is easier to engineer models that can simultaneously (i) be compatible with constraints on the primordial spectral index, which tends to otherwise disfavor hybrid models, and (ii) produce a spike on astrophysically large length scales. The latter may have significant consequences, possibly seeding the formation of astrophysically large black holes. We calculate correlation functions of the time-delay, a measure of density perturbations, produced by the waterfall fields, as a convergent power series in both 1 / N and the field's correlation function Δ (x). We show that for large N, the two-point function is < δt (x) δt (0) > ∝Δ2 (| x |) / N and the three-point function is < δt (x) δt (y) δt (0) > ∝ Δ (| x - y |) Δ (| x |) Δ (| y |) /N2. In accordance with the central limit theorem, the density perturbations on the scale of the spike are Gaussian for large N and non-Gaussian for small N.

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

NASA Astrophysics Data System (ADS)

Atta-Fynn, Raymond; Ray, Asok K.

2009-11-01

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

Density-functional theory applied to d- and f-electron systems

NASA Astrophysics Data System (ADS)

Wu, Xueyuan

Density functional theory (DFT) has been applied to study the electronic and geometric structures of prototype d- and f-electron systems. For the d-electron system, all electron DFT with gradient corrections to the exchange and correlation functionals has been used to investigate the properties of small neutral and cationic vanadium clusters. Results are in good agreement with available experimental and other theoretical data. For the f-electron system, a hybrid DFT, namely, B3LYP (Becke's 3-parameter hybrid functional using the correlation functional of Lee, Yang and Parr) with relativistic effective core potentials and cluster models has been applied to investigate the nature of chemical bonding of both the bulk and the surfaces of plutonium monoxide and dioxide. Using periodic models, the electronic and geometric structures of PuO2 and its (110) surface, as well as water adsorption on this surface have also been investigated using DFT in both local density approximation (LDA) and generalized gradient approximation (GGA) formalisms.

Generalization of dielectric-dependent hybrid functionals to finite systems

DOE PAGES

Brawand, Nicholas P.; Voros, Marton; Govoni, Marco; ...

2016-10-04

The accurate prediction of electronic and optical properties of molecules and solids is a persistent challenge for methods based on density functional theory. We propose a generalization of dielectric-dependent hybrid functionals to finite systems where the definition of the mixing fraction of exact and semilocal exchange is physically motivated, nonempirical, and system dependent. The proposed functional yields ionization potentials, and fundamental and optical gaps of many, diverse molecular systems in excellent agreement with experiments, including organic and inorganic molecules and semiconducting nanocrystals. As a result, we further demonstrate that this hybrid functional gives the correct alignment between energy levels ofmore » the exemplary TTF-TCNQ donor-acceptor system.« less

Understanding the electronic structure of CdSe quantum dot-fullerene (C{sub 60}) hybrid nanostructure for photovoltaic applications

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

Sarkar, Sunandan; Rajbanshi, Biplab; Sarkar, Pranab, E-mail: pranab.sarkar@visva-bharati.ac.in

2014-09-21

By using the density-functional tight binding method, we studied the electronic structure of CdSe quantum dot(QD)-buckminsterfullerene (C{sub 60}) hybrid systems as a function of both the size of the QD and concentration of the fullerene molecule. Our calculation reveals that the lowest unoccupied molecular orbital energy level of the hybrid CdSeQD-C{sub 60} systems lies on the fullerene moiety, whereas the highest occupied molecular orbital (HOMO) energy level lies either on the QD or the fullerene depending on size of the CdSe QD. We explored the possibility of engineering the energy level alignment by varying the size of the CdSe QD.more » With increase in size of the QD, the HOMO level is shifted upward and crosses the HOMO level of the C{sub 60}-thiol molecule resulting transition from the type-I to type-II band energy alignment. The density of states and charge density plot support these types of band gap engineering of the CdSe-C{sub 60} hybrid systems. This type II band alignment indicates the possibility of application of this nanohybrid for photovoltaic purpose.« less

Spin-Multiplet Components and Energy Splittings by Multistate Density Functional Theory.

PubMed

Grofe, Adam; Chen, Xin; Liu, Wenjian; Gao, Jiali

2017-10-05

Kohn-Sham density functional theory has been tremendously successful in chemistry and physics. Yet, it is unable to describe the energy degeneracy of spin-multiplet components with any approximate functional. This work features two contributions. (1) We present a multistate density functional theory (MSDFT) to represent spin-multiplet components and to determine multiplet energies. MSDFT is a hybrid approach, taking advantage of both wave function theory and density functional theory. Thus, the wave functions, electron densities and energy density-functionals for ground and excited states and for different components are treated on the same footing. The method is illustrated on valence excitations of atoms and molecules. (2) Importantly, a key result is that for cases in which the high-spin components can be determined separately by Kohn-Sham density functional theory, the transition density functional in MSDFT (which describes electronic coupling) can be defined rigorously. The numerical results may be explored to design and optimize transition density functionals for configuration coupling in multiconfigurational DFT.

Combined hybrid functional and DFT+U calculations for metal chalcogenides

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

Aras, Mehmet; Kılıç, Çetin, E-mail: cetin-kilic@gyte.edu.tr

2014-07-28

In the density-functional studies of materials with localized electronic states, the local/semilocal exchange-correlation functionals are often either combined with a Hubbard parameter U as in the LDA+U method or mixed with a fraction of exactly computed (Fock) exchange energy yielding a hybrid functional. Although some inaccuracies of the semilocal density approximations are thus fixed to a certain extent, the improvements are not sufficient to make the predictions agree with the experimental data. Here, we put forward the perspective that the hybrid functional scheme and the LDA+U method should be treated as complementary, and propose to combine the range-separated Heyd-Scuseria-Ernzerhof (HSE)more » hybrid functional with the Hubbard U. We thus present a variety of HSE+U calculations for a set of II-VI semiconductors, consisting of zinc and cadmium monochalcogenides, along with comparison to the experimental data. Our findings imply that an optimal value U{sup *} of the Hubbard parameter could be determined, which ensures that the HSE+U{sup *} calculation reproduces the experimental band gap. It is shown that an improved description not only of the electronic structure but also of the crystal structure and energetics is obtained by adding the U{sup *} term to the HSE functional, proving the utility of HSE+U{sup *} approach in modeling semiconductors with localized electronic states.« less

How Accurate Are the Minnesota Density Functionals for Noncovalent Interactions, Isomerization Energies, Thermochemistry, and Barrier Heights Involving Molecules Composed of Main-Group Elements?

DOE PAGES

Mardirossian, Narbe; Head-Gordon, Martin

2016-08-18

The 14 Minnesota density functionals published between the years 2005 and early 2016 are benchmarked on a comprehensive database of 4986 data points (84 data sets) involving molecules composed of main-group elements. The database includes noncovalent interactions, isomerization energies, thermochemistry, and barrier heights, as well as equilibrium bond lengths and equilibrium binding energies of noncovalent dimers. Additionally, the sensitivity of the Minnesota density functionals to the choice of basis set and integration grid is explored for both noncovalent interactions and thermochemistry. By and large, the main strength of the hybrid Minnesota density functionals is that the best ones provide verymore » good performance for thermochemistry (e.g., M06-2X), barrier heights (e.g., M08-HX, M08-SO, MN15), and systems heavily characterized by self-interaction error (e.g., M06-2X, M08-HX, M08-SO, MN15), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-2X is recommended from the 10 hybrid Minnesota functionals). Similarly, the main strength of the local Minnesota density functionals is that the best ones provide very good performance for thermochemistry (e.g., MN15-L), barrier heights (e.g., MN12-L), and systems heavily characterized by self-interaction error (e.g., MN12-L and MN15-L), while the main weakness is that none of them are state-of-the-art for the full spectrum of noncovalent interactions and isomerization energies (although M06-L is clearly the best from the four local Minnesota functionals). Finally, as an overall guide, M06-2X and MN15 are perhaps the most broadly useful hybrid Minnesota functionals, while M06-L and MN15-L are perhaps the most broadly useful local Minnesota functionals, although each has different strengths and weaknesses.« less

Hybrid density functional study on the mechanism for the enhanced photocatalytic properties of the ultrathin hybrid layered nanocomposite g-C3N4/BiOCl

NASA Astrophysics Data System (ADS)

Yao, Wenzhi; Zhang, Jihua; Wang, Yuanxu; Ren, Fengzhu

2018-03-01

To investigate the origin of the high photocatalytic performance of experimentally synthesized g-C3N4/ BiOCl, we studied its geometry structure, electronic structure, and photocatalytic properties by means of hybrid density-functional theory (DFT). The calculated band alignment of g-C3N4 and few-layer BiOCl sheets clearly shows that g-C3N4/ BiOCl is a standard type-II nanocomposite. The density of states, Bader charge, partial charge density, charge density difference, and the effective masses show that electron-hole pair can be effectively separated in the g-C3N4/BiOCl interface. The calculated absorption coefficients indicate an obvious redshift of the absorption edge. The band gap of g-C3N4/BiOCl can be modulated by external electric field, and a semiconductor-semimetal transition is observed. The type-II vdW heterostructure is still maintained during the changes of external electric field. Especially, when the electric field reaches to +0.7 V/Å, the impurity states have been eliminated with the band gap of 2.3 eV. An analysis of optical properties shows that the absorption coefficient in the visible-light region is enhanced considerably as the electric-field strength increases. Our calculation results suggest that the ultrathin hybrid layered g-C3N4/BiOCl nanocomposite may have significant advantages for visible-light photocatalysis.

Hybrid density functional study of band alignment in ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures.

PubMed

Wang, Zhenhai; Zhao, Mingwen; Wang, Xiaopeng; Xi, Yan; He, Xiujie; Liu, Xiangdong; Yan, Shishen

2012-12-05

The band alignment in ZnO-GaN and related heterostructures is crucial for uses in solar harvesting technology. Here, we report our density functional calculations of the band alignment and optical properties of ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures using a Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. We found that the conventional GGA functionals underestimate not only the band gap but also the band offset of these heterostructures. Using the hybrid functional calculations, we show that the (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution has a direct band gap of about 2.608 eV, in good agreement with the experimental data. More importantly, this solid solution forms type-II band alignment with the host materials. A GaN-(Ga(1-x)Zn(x))(N(1-x)O(x))-ZnO core-shell solar cell model is presented to improve the visible light absorption ability and carrier collection efficiency.

Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework.

PubMed

Berger, Daniel; Logsdail, Andrew J; Oberhofer, Harald; Farrow, Matthew R; Catlow, C Richard A; Sherwood, Paul; Sokol, Alexey A; Blum, Volker; Reuter, Karsten

2014-07-14

We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capability by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO2(110).

Embedded-cluster calculations in a numeric atomic orbital density-functional theory framework

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

Berger, Daniel, E-mail: daniel.berger@ch.tum.de; Oberhofer, Harald; Reuter, Karsten

2014-07-14

We integrate the all-electron electronic structure code FHI-aims into the general ChemShell package for solid-state embedding quantum and molecular mechanical (QM/MM) calculations. A major undertaking in this integration is the implementation of pseudopotential functionality into FHI-aims to describe cations at the QM/MM boundary through effective core potentials and therewith prevent spurious overpolarization of the electronic density. Based on numeric atomic orbital basis sets, FHI-aims offers particularly efficient access to exact exchange and second order perturbation theory, rendering the established QM/MM setup an ideal tool for hybrid and double-hybrid level density functional theory calculations of solid systems. We illustrate this capabilitymore » by calculating the reduction potential of Fe in the Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for (photo-)catalytic water oxidation at TiO{sub 2}(110)« less

Electronic structure of stoichiometric and reduced ZnO from periodic relativistic all electron hybrid density functional calculations using numeric atom-centered orbitals.

PubMed

Viñes, Francesc; Illas, Francesc

2017-03-30

The atomic and electronic structure of stoichiometric and reduced ZnO wurtzite has been studied using a periodic relativistic all electron hybrid density functional (PBE0) approach and numeric atom-centered orbital basis set with quality equivalent to aug-cc-pVDZ. To assess the importance of relativistic effects, calculations were carried out without and with explicit inclusion of relativistic effects through the zero order regular approximation. The calculated band gap is ∼0.2 eV smaller than experiment, close to previous PBE0 results including relativistic calculation through the pseudopotential and ∼0.25 eV smaller than equivalent nonrelativistic all electron PBE0 calculations indicating possible sources of error in nonrelativistic all electron density functional calculations for systems containing elements with relatively high atomic number. The oxygen vacancy formation energy converges rather fast with the supercell size, the predicted value agrees with previously hybrid density functional calculations and analysis of the electronic structure evidences the presence of localized electrons at the vacancy site with a concomitant well localized peak in the density of states ∼0.5 eV above the top of the valence band and a significant relaxation of the Zn atoms near to the oxygen vacancy. Finally, present work shows that accurate results can be obtained in systems involving large supercells containing up to ∼450 atoms using a numeric atomic-centered orbital basis set within a full all electron description including scalar relativistic effects at an affordable cost. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Electronic properties of CdWO{sub 4}: Use of hybrid exchange and correlation functionals

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

Meena, B. S., E-mail: bsmphysics@gmail.com; Mund, H. S.; Ahuja, B. L.

Energy bands, density of states (DOS), Mulliken population (MP) and electron momentum densities (EMDs) of CdWO{sub 4} are presented using hybrid exchange and correlation functionals namely B3LYP, B3PW and PBE0. To validate the present hybrid potentials, theoretical EMDs have been compared with the experimental Compton profile. It is found that LCAO-B3LYP based Compton profile gives a better agreement with experiment than other theoretical profiles. The energy bands and DOS show a wide band gap semiconducting nature of CdWO{sub 4}. The theoretical band gap obtained using B3LYP scheme reconciles well with the available experimental data. In addition, we have also presentedmore » the anisotropies in EMDs along [100], [110] and [001] directions and the bonding effects using the MP data.« less

Functionalized carbon nanotube based hybrid electrochemical capacitors using neutral bromide redox-active electrolyte for enhancing energy density

NASA Astrophysics Data System (ADS)

Tang, Xiaohui; Lui, Yu Hui; Chen, Bolin; Hu, Shan

2017-06-01

A hybrid electrochemical capacitor (EC) with enhanced energy density is realized by integrating functionalized carbon nanotube (FCNT) electrodes with redox-active electrolyte that has a neutral pH value (1 M Na2SO4 and 0.5 M KBr mixed aqueous solution). The negative electrode shows an electric double layer capacitor-type behavior. On the positive electrode, highly reversible Br-/Br3- redox reactions take place, presenting a battery-type behavior, which contributes to increase the capacitance of the hybrid cell. The voltage window of the whole cell is extended up to 1.5 V because of the high over-potentials of oxygen and hydrogen evolution reactions in the neutral electrolyte. Compared with raw CNT, the FCNT has better wettability in the aqueous electrolyte and contributes to increase the electric double layer capacitance of the cell. As a result, the maximum energy density of 28.3 Wh kg-1 is obtained from the hybrid EC at 0.5 A g-1 without sacrificing its power density, which is around 4 times larger than that of the electrical double layer capacitor constructed by FCNT electrodes and 1 M Na2SO4 electrolyte. Moreover, the discharge capacity retained 86.3% of its initial performance after 10000 cycles of galvanostatic charge and discharge test (10 A/g), suggesting its long life cycle even at high current loading.

Electronic structure modeling of InAs/GaSb superlattices with hybrid density functional theory

NASA Astrophysics Data System (ADS)

Garwood, T.; Modine, N. A.; Krishna, S.

2017-03-01

The application of first-principles calculations holds promise for greatly improving our understanding of semiconductor superlattices. Developing a procedure to accurately predict band gaps using hybrid density functional theory lays the groundwork for future studies investigating more nuanced properties of these structures. Our approach allows a priori prediction of the properties of SLS structures using only the band gaps of the constituent materials. Furthermore, it should enable direct investigation of the effects of interface structure, e.g., intermixing or ordering at the interface, on SLS properties. In this paper, we present band gap data for various InAs/GaSb type-II superlattice structures calculated using the generalized Kohn-Sham formulation of density functional theory. A PBE0-type hybrid functional was used, and the portion of the exact exchange was tuned to fit the band gaps of the binary compounds InAs and GaSb with the best agreement to bulk experimental values obtained with 18% of the exact exchange. The heterostructures considered in this study are 6 monolayer (ML) InAs/6 ML GaSb, 8 ML InAs/8 ML GaSb and 10 ML InAs/10 ML GaSb with deviations from the experimental band gaps ranging from 3% to 11%.

Electronic structure modeling of InAs/GaSb superlattices with hybrid density functional theory

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

Garwood, Tristan; Modine, Normand A.; Krishna, S.

2016-12-18

The application of first-principles calculations holds promise for greatly improving our understanding of semiconductor superlattices. By developing a procedure to accurately predict band gaps using hybrid density functional theory, it lays the groundwork for future studies investigating more nuanced properties of these structures. Our approach allows a priori prediction of the properties of SLS structures using only the band gaps of the constituent materials. Furthermore, it should enable direct investigation of the effects of interface structure, e.g., intermixing or ordering at the interface, on SLS properties. In this paper, we present band gap data for various InAs/GaSb type-II superlattice structuresmore » calculated using the generalized Kohn-Sham formulation of density functional theory. A PBE0-type hybrid functional was used, and the portion of the exact exchange was tuned to fit the band gaps of the binary compounds InAs and GaSb with the best agreement to bulk experimental values obtained with 18% of the exact exchange. The heterostructures considered in this study are 6 monolayer (ML) InAs/6 ML GaSb, 8 ML InAs/8 ML GaSb and 10 ML InAs/10 ML GaSb with deviations from the experimental band gaps ranging from 3% to 11%.« less

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

NASA Astrophysics Data System (ADS)

Polo, Victor; Kraka, Elfi; Cremer, Dieter

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

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.

Thermodynamics of RNA structures by Wang–Landau sampling

PubMed Central

Lou, Feng; Clote, Peter

2010-01-01

Motivation: Thermodynamics-based dynamic programming RNA secondary structure algorithms have been of immense importance in molecular biology, where applications range from the detection of novel selenoproteins using expressed sequence tag (EST) data, to the determination of microRNA genes and their targets. Dynamic programming algorithms have been developed to compute the minimum free energy secondary structure and partition function of a given RNA sequence, the minimum free-energy and partition function for the hybridization of two RNA molecules, etc. However, the applicability of dynamic programming methods depends on disallowing certain types of interactions (pseudoknots, zig-zags, etc.), as their inclusion renders structure prediction an nondeterministic polynomial time (NP)-complete problem. Nevertheless, such interactions have been observed in X-ray structures. Results: A non-Boltzmannian Monte Carlo algorithm was designed by Wang and Landau to estimate the density of states for complex systems, such as the Ising model, that exhibit a phase transition. In this article, we apply the Wang-Landau (WL) method to compute the density of states for secondary structures of a given RNA sequence, and for hybridizations of two RNA sequences. Our method is shown to be much faster than existent software, such as RNAsubopt. From density of states, we compute the partition function over all secondary structures and over all pseudoknot-free hybridizations. The advantage of the WL method is that by adding a function to evaluate the free energy of arbitary pseudoknotted structures and of arbitrary hybridizations, we can estimate thermodynamic parameters for situations known to be NP-complete. This extension to pseudoknots will be made in the sequel to this article; in contrast, the current article describes the WL algorithm applied to pseudoknot-free secondary structures and hybridizations. Availability: The WL RNA hybridization web server is under construction at http://bioinformatics.bc.edu/clotelab/. Contact: clote@bc.edu PMID:20529917

The electrical and thermal transport properties of hybrid zigzag graphene-BN nanoribbons

NASA Astrophysics Data System (ADS)

Gao, Song; Lu, Wei; Zheng, Guo-Hui; Jia, Yalei; Ke, San-Huang

2017-06-01

The electron and phonon transport in hybrid graphene-BN zigzag nanoribbons are investigated by the nonequilibrium Green’s function method combined with density functional theory calculations. A 100% spin-polarized electron transport in a large energy window around the Fermi level is found and this behavior is independent of the ribbon width as long as there contain 3 zigzag carbon chains. The phonon transport calculations show that the ratio of C-chain number to BN-chain number will modify the thermal conductance of the hybrid nanoribbon in a complicated manner.

Density matrix renormalization group with efficient dynamical electron correlation through range separation

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

Hedegård, Erik Donovan, E-mail: erik.hedegard@phys.chem.ethz.ch; Knecht, Stefan; Reiher, Markus, E-mail: markus.reiher@phys.chem.ethz.ch

2015-06-14

We present a new hybrid multiconfigurational method based on the concept of range-separation that combines the density matrix renormalization group approach with density functional theory. This new method is designed for the simultaneous description of dynamical and static electron-correlation effects in multiconfigurational electronic structure problems.

Description of plasmon-like band in silver clusters: the importance of the long-range Hartree-Fock exchange in time-dependent density-functional theory simulations.

PubMed

Rabilloud, Franck

2014-10-14

Absorption spectra of Ag20 and Ag55(q) (q = +1, -3) nanoclusters are investigated in the framework of the time-dependent density functional theory in order to analyse the role of the d electrons in plasmon-like band of silver clusters. The description of the plasmon-like band from calculations using density functionals containing an amount of Hartree-Fock exchange at long range, namely, hybrid and range-separated hybrid (RSH) density functionals, is in good agreement with the classical interpretation of the plasmon-like structure as a collective excitation of valence s-electrons. In contrast, using local or semi-local exchange functionals (generalized gradient approximations (GGAs) or meta-GGAs) leads to a strong overestimation of the role of d electrons in the plasmon-like band. The semi-local asymptotically corrected model potentials also describe the plasmon as mainly associated to d electrons, though calculated spectra are in fairly good agreement with those calculated using the RSH scheme. Our analysis shows that a portion of non-local exchange modifies the description of the plasmon-like band.

Analysis of Different Cost Functions in the Geosect Airspace Partitioning Tool

NASA Technical Reports Server (NTRS)

Wong, Gregory L.

2010-01-01

A new cost function representing air traffic controller workload is implemented in the Geosect airspace partitioning tool. Geosect currently uses a combination of aircraft count and dwell time to select optimal airspace partitions that balance controller workload. This is referred to as the aircraft count/dwell time hybrid cost function. The new cost function is based on Simplified Dynamic Density, a measure of different aspects of air traffic controller workload. Three sectorizations are compared. These are the current sectorization, Geosect's sectorization based on the aircraft count/dwell time hybrid cost function, and Geosect s sectorization based on the Simplified Dynamic Density cost function. Each sectorization is evaluated for maximum and average workload along with workload balance using the Simplified Dynamic Density as the workload measure. In addition, the Airspace Concept Evaluation System, a nationwide air traffic simulator, is used to determine the capacity and delay incurred by each sectorization. The sectorization resulting from the Simplified Dynamic Density cost function had a lower maximum workload measure than the other sectorizations, and the sectorization based on the combination of aircraft count and dwell time did a better job of balancing workload and balancing capacity. However, the current sectorization had the lowest average workload, highest sector capacity, and the least system delay.

Hybrid density functional theory band structure engineering in hematite

NASA Astrophysics Data System (ADS)

Pozun, Zachary D.; Henkelman, Graeme

2011-06-01

We present a hybrid density functional theory (DFT) study of doping effects in α-Fe2O3, hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that using a screened functional that smoothly transitions from 12% exact exchange at short ranges to standard DFT at long range accurately reproduces the experimental band gap and other material properties. We then show that the antiferromagnetic symmetry in the pure α-Fe2O3 crystal is broken by all dopants and that the ligand field theory correctly predicts local magnetic moments on the dopants. We characterize the resulting band gaps for hematite doped by transition metals and the p-block post-transition metals. The specific case of Pd doping is investigated in order to correlate calculated doping energies and optical properties with experimentally observed photocatalytic behavior.

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.

Few layered vanadyl phosphate nano sheets-MWCNT hybrid as an electrode material for supercapacitor application

NASA Astrophysics Data System (ADS)

Dutta, Shibsankar; De, Sukanta

2016-05-01

It have been already seen that 2-dimensional nano materials are the suitable choice for the supercapacitor application due to their large specific surface area, electrochemical active sites, micromechanical flexibility, expedite ion migration channel properties. Free standing hybrid films of functionalized MWCNT (- COOH group) and α-Vanadyl phosphates (VOPO42H2O) are prepared by vacuum filtering. The surface morphology and microstructure of the samples are studied by transmission electron microscope, field emission scanning electron microscope, XRD, Electrochemical properties of hybrid films have been investigated systematically in 1M Na2SO4 aqueous electrolyte. The hybrid material exhibits a high specific capacitance 236 F/g with high energy density of 65.6 Wh/Kg and a power density of 1476 W/Kg.

Semilocal density functional obeying a strongly tightened bound for exchange

PubMed Central

Sun, Jianwei; Perdew, John P.; Ruzsinszky, Adrienn

2015-01-01

Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb–Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic “meta-GGA made very simple” (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew–Burke–Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules. PMID:25561554

Semilocal density functional obeying a strongly tightened bound for exchange.

PubMed

Sun, Jianwei; Perdew, John P; Ruzsinszky, Adrienn

2015-01-20

Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb-Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic "meta-GGA made very simple" (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew-Burke-Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules.

Efficient self-assembly of DNA-functionalized fluorophores and gold nanoparticles with DNA functionalized silicon surfaces: the effect of oligomer spacers

PubMed Central

Milton, James A.; Patole, Samson; Yin, Huabing; Xiao, Qiang; Brown, Tom; Melvin, Tracy

2013-01-01

Although strategies for the immobilization of DNA oligonucleotides onto surfaces for bioanalytical and top-down bio-inspired nanobiofabrication approaches are well developed, the effect of introducing spacer molecules between the surface and the DNA oligonucleotide for the hybridization of nanoparticle–DNA conjugates has not been previously assessed in a quantitative manner. The hybridization efficiency of DNA oligonucleotides end-labelled with gold nanoparticles (1.4 or 10 nm diameter) with DNA sequences conjugated to silicon surfaces via hexaethylene glycol phosphate diester oligomer spacers (0, 1, 2, 6 oligomers) was found to be independent of spacer length. To quantify both the density of DNA strands attached to the surfaces and hybridization with the surface-attached DNA, new methodologies have been developed. Firstly, a simple approach based on fluorescence has been developed for determination of the immobilization density of DNA oligonucleotides. Secondly, an approach using mass spectrometry has been created to establish (i) the mean number of DNA oligonucleotides attached to the gold nanoparticles and (ii) the hybridization density of nanoparticle–oligonucleotide conjugates with the silicon surface–attached complementary sequence. These methods and results will be useful for application with nanosensors, the self-assembly of nanoelectronic devices and the attachment of nanoparticles to biomolecules for single-molecule biophysical studies. PMID:23361467

Room-temperature d0 ferromagnetism in carbon-doped Y2O3 for spintronic applications: A density functional theory study

NASA Astrophysics Data System (ADS)

Chakraborty, Brahmananda; Nandi, Prithwish K.; Kawazoe, Yoshiyuki; Ramaniah, Lavanya M.

2018-05-01

Through density functional theory simulations with the generalized gradient approximation, confirmed by the more sophisticated hybrid functional, we predict the triggering of d0 ferromagnetism in C doped Y2O3 at a hole density of 3.36 ×1021c m-3 (one order less than the critical hole density of ZnO) having magnetic moment of 2.0 μB per defect with ferromagnetic coupling large enough to promote room-temperature ferromagnetism. The persistence of ferromagnetism at room temperature is established through computation of the Curie temperature by the mean field approximation and ab initio molecular dynamics simulations. The induced magnetic moment is mainly contributed by the 2 p orbital of the impurity C and the 2 p orbital of O and we quantitatively and extensively demonstrate through the analysis of density of states and ferromagnetic coupling that the Stoner criterion is satisfied to activate room-temperature ferromagnetism. As the system is stable at room temperature, C doped Y2O3 has feasible defect formation energy and ferromagnetism survives for the choice of hybrid exchange functional, and at room temperature we strongly believe that C doped Y2O3 can be tailored as a room-temperature diluted magnetic semiconductor for spintronic applications.

Stochastic Optimally Tuned Range-Separated Hybrid Density Functional Theory.

PubMed

Neuhauser, Daniel; Rabani, Eran; Cytter, Yael; Baer, Roi

2016-05-19

We develop a stochastic formulation of the optimally tuned range-separated hybrid density functional theory that enables significant reduction of the computational effort and scaling of the nonlocal exchange operator at the price of introducing a controllable statistical error. Our method is based on stochastic representations of the Coulomb convolution integral and of the generalized Kohn-Sham density matrix. The computational cost of the approach is similar to that of usual Kohn-Sham density functional theory, yet it provides a much more accurate description of the quasiparticle energies for the frontier orbitals. This is illustrated for a series of silicon nanocrystals up to sizes exceeding 3000 electrons. Comparison with the stochastic GW many-body perturbation technique indicates excellent agreement for the fundamental band gap energies, good agreement for the band edge quasiparticle excitations, and very low statistical errors in the total energy for large systems. The present approach has a major advantage over one-shot GW by providing a self-consistent Hamiltonian that is central for additional postprocessing, for example, in the stochastic Bethe-Salpeter approach.

Development of multicomponent hybrid density functional theory with polarizable continuum model for the analysis of nuclear quantum effect and solvent effect on NMR chemical shift.

PubMed

Kanematsu, Yusuke; Tachikawa, Masanori

2014-04-28

We have developed the multicomponent hybrid density functional theory [MC_(HF+DFT)] method with polarizable continuum model (PCM) for the analysis of molecular properties including both nuclear quantum effect and solvent effect. The chemical shifts and H/D isotope shifts of the picolinic acid N-oxide (PANO) molecule in chloroform and acetonitrile solvents are applied by B3LYP electron exchange-correlation functional for our MC_(HF+DFT) method with PCM (MC_B3LYP/PCM). Our MC_B3LYP/PCM results for PANO are in reasonable agreement with the corresponding experimental chemical shifts and isotope shifts. We further investigated the applicability of our method for acetylacetone in several solvents.

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

PubMed

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

2017-11-15

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

Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery

PubMed Central

Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

2016-01-01

α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm−2. At 1.0 V of cell voltage, a current density of 324 mA cm−2 is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm−2, and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte. PMID:27646032

Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery.

PubMed

Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

2016-09-20

α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm(-2). At 1.0 V of cell voltage, a current density of 324 mA cm(-2) is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm(-2), and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte.

Effects of Varied Housing Density on a Hybrid Mouse Strain Followed for 20 Months

PubMed Central

Currer, Joanne M.

2016-01-01

To evaluate the effect of increased housing density in a hybrid mouse strain, we evaluated a panel of physiological and behavioral traits in animals that were housed in groups of 3, 5, 8, or 12, using cages that provide 78.1 in2 of floor space. Such groupings resulted in cage densities that ranged from half to almost twice the density recommended by the Guide for the Care and Use of Laboratory Animals. While previous studies have investigated physiological effects of increased housing density using inbred mouse strains, including C57BL/6J and 129S1/SvImJ, this study tested an F1 hybrid population of C57BL/6J x 129S1/SvImJ for changes resulting from either decreased or increased housing density. Mice were followed until they were 20 months old, a substantially longer duration than has been used in previous density studies. We evaluated mortality, growth, home cage behavior, blood pressure, body composition, clinical plasma chemistries, immune function, and organ weights (heart, kidney, adrenal glands, and testes) as endpoints of chronic stress that may arise from sub-optimal housing conditions. Few statistically different parameters were observed in this study, none of which describe chronic stress and all within normal physiological ranges for research mice, suggesting that this hybrid strain was not adversely affected by housing at twice the density currently recommended. PMID:26900840

Invited Paper - Density functional theory: coverage of dynamic and non-dynamic electron correlation effects

NASA Astrophysics Data System (ADS)

Cremer, Dieter

The electron correlation effects covered by density functional theory (DFT) can be assessed qualitatively by comparing DFT densities ρ(r) with suitable reference densities obtained with wavefunction theory (WFT) methods that cover typical electron correlation effects. The analysis of difference densities ρ(DFT)-ρ(WFT) reveals that LDA and GGA exchange (X) functionals mimic non-dynamic correlation effects in an unspecified way. It is shown that these long range correlation effects are caused by the self-interaction error (SIE) of standard X functionals. Self-interaction corrected (SIC) DFT exchange gives, similar to exact exchange, for the bonding region a delocalized exchange hole, and does not cover any correlation effects. Hence, the exchange SIE is responsible for the fact that DFT densities often resemble MP4 or MP2 densities. The correlation functional changes X-only DFT densities in a manner observed when higher order coupling effects between lower order N-electron correlation effects are included. Hybrid functionals lead to changes in the density similar to those caused by SICDFT, which simply reflects the fact that hybrid functionals have been developed to cover part of the SIE and its long range correlation effects in a balanced manner. In the case of spin-unrestricted DFT (UDFT), non-dynamic electron correlation effects enter the calculation both via the X functional and via the wavefunction, which may cause a double-counting of correlation effects. The use of UDFT in the form of permuted orbital and broken-symmetry DFT (PO-UDFT, BS-UDFT) can lead to reasonable descriptions of multireference systems provided certain conditions are fulfilled. More reliable, however, is a combination of DFT and WFT methods, which makes the routine description of multireference systems possible. The development of such methods implies a separation of dynamic and non-dynamic correlation effects. Strategies for accomplishing this goal are discussed in general and tested in practice for CAS (complete active space)-DFT.

Electronic properties of B and Al doped graphane: A hybrid density functional study

NASA Astrophysics Data System (ADS)

Mapasha, R. E.; Igumbor, E.; Andriambelaza, N. F.; Chetty, N.

2018-04-01

Using a hybrid density functional theory approach parametrized by Heyd, Scuseria and Ernzerhof (HSE06 hybrid functional), we study the energetics, structural and electronic properties of a graphane monolayer substitutionally doped with the B (BCH) and Al (AlCH) atoms. The BCH defect can be integrated within a graphane monolayer at a relative low formation energy, without major structural distortions and symmetry breaking. The AlCH defect relaxes outward of the monolayer and breaks the symmetry. The density of states plots indicate that BCH doped graphane monolayer is a wide band gap semiconductor, whereas the AlCH defect introduces the spin dependent mid gap states at the vicinity of the Fermi level, revealing a metallic character with the pronounced magnetic features. We further examine the response of the Al dependent spin states on the multiple charge states doping. We find that the defect formation energy, structural and electronic properties can be altered via charge state modulation. The +1 charge doping opens an energy band gap of 1.75 eV. This value corresponds to the wavelength in the visible spectrum, suggesting an ideal material for solar cell absorbers. Our study fine tunes the graphane band gap through the foreign atom doping as well as via defect charge state modulation.

Importance of the correlation contribution for local hybrid functionals: range separation and self-interaction corrections.

PubMed

Arbuznikov, Alexei V; Kaupp, Martin

2012-01-07

Local hybrid functionals with their position-dependent exact-exchange admixture are a conceptually simple and promising extension of the concept of a hybrid functional. Local hybrids based on a simple mixing of the local spin density approximation (LSDA) with exact exchange have been shown to be successful for thermochemistry, reaction barriers, and a range of other properties. So far, the combination of this generation of local hybrids with an LSDA correlation functional has been found to give the most favorable results for atomization energies, for a range of local mixing functions (LMFs) governing the exact-exchange admixture. Here, we show that the choice of correlation functional to be used with local hybrid exchange crucially influences the parameterization also of the exchange part as well as the overall performance. A novel ansatz for the correlation part of local hybrids is suggested based on (i) range-separation of LSDA correlation into short-range (SR) and long-range (LR) parts, and (ii) partial or full elimination of the one-electron self-correlation from the SR part. It is shown that such modified correlation functionals allow overall larger exact exchange admixture in thermochemically competitive local hybrids than before. This results in improvements for reaction barriers and for other properties crucially influenced by self-interaction errors, as demonstrated by a number of examples. Based on the range-separation approach, a fresh view on the breakdown of the correlation energy into dynamical and non-dynamical parts is suggested.

Communication: xDH double hybrid functionals can be qualitatively incorrect for non-equilibrium geometries: Dipole moment inversion and barriers to radical-radical association using XYG3 and XYGJ-OS

NASA Astrophysics Data System (ADS)

Hait, Diptarka; Head-Gordon, Martin

2018-05-01

Double hybrid (DH) density functionals are amongst the most accurate density functional approximations developed so far, largely due to the incorporation of correlation effects from unoccupied orbitals via second order perturbation theory (PT2). The xDH family of DH functionals calculate energy directly from orbitals optimized by a lower level approach like B3LYP, without self-consistent optimization. XYG3 and XYGJ-OS are two widely used xDH functionals that are known to be quite accurate at equilibrium geometries. Here, we show that the XYG3 and XYGJ-OS functionals can be ill behaved for stretched bonds well beyond the Coulson-Fischer point, predicting unphysical dipole moments and humps in potential energy curves for some simple systems like the hydrogen fluoride molecule. Numerical experiments and analysis show that these failures are not due to PT2. Instead, a large mismatch at stretched bond-lengths between the reference B3LYP orbitals and the optimized orbitals associated with the non-PT2 part of XYG3 leads to an unphysically large non-Hellman-Feynman contribution to first order properties like forces and electron densities.

Few layered vanadyl phosphate nano sheets-MWCNT hybrid as an electrode material for supercapacitor application

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

Dutta, Shibsankar; De, Sukanta, E-mail: sukanta.physics@presiuniv.ac.in

It have been already seen that 2-dimensional nano materials are the suitable choice for the supercapacitor application due to their large specific surface area, electrochemical active sites, micromechanical flexibility, expedite ion migration channel properties. Free standing hybrid films of functionalized MWCNT (– COOH group) and α-Vanadyl phosphates (VOPO{sub 4}2H{sub 2}O) are prepared by vacuum filtering. The surface morphology and microstructure of the samples are studied by transmission electron microscope, field emission scanning electron microscope, XRD, Electrochemical properties of hybrid films have been investigated systematically in 1M Na{sub 2}SO{sub 4} aqueous electrolyte. The hybrid material exhibits a high specific capacitance 236more » F/g with high energy density of 65.6 Wh/Kg and a power density of 1476 W/Kg.« less

Nuclear magnetic resonance spin-spin coupling constants from coupled perturbed density functional theory

NASA Astrophysics Data System (ADS)

Sychrovský, Vladimír; Gräfenstein, Jürgen; Cremer, Dieter

2000-09-01

For the first time, a complete implementation of coupled perturbed density functional theory (CPDFT) for the calculation of NMR spin-spin coupling constants (SSCCs) with pure and hybrid DFT is presented. By applying this method to several hydrides, hydrocarbons, and molecules with multiple bonds, the performance of DFT for the calculation of SSCCs is analyzed in dependence of the XC functional used. The importance of electron correlation effects is demonstrated and it is shown that the hybrid functional B3LYP leads to the best accuracy of calculated SSCCs. Also, CPDFT is compared with sum-over-states (SOS) DFT where it turns out that the former method is superior to the latter because it explicitly considers the dependence of the Kohn-Sham operator on the perturbed orbitals in DFT when calculating SSCCs. The four different coupling mechanisms contributing to the SSCC are discussed in connection with the electronic structure of the molecule.

Local electric dipole moments for periodic systems via density functional theory embedding.

PubMed

Luber, Sandra

2014-12-21

We describe a novel approach for the calculation of local electric dipole moments for periodic systems. Since the position operator is ill-defined in periodic systems, maximally localized Wannier functions based on the Berry-phase approach are usually employed for the evaluation of local contributions to the total electric dipole moment of the system. We propose an alternative approach: within a subsystem-density functional theory based embedding scheme, subset electric dipole moments are derived without any additional localization procedure, both for hybrid and non-hybrid exchange-correlation functionals. This opens the way to a computationally efficient evaluation of local electric dipole moments in (molecular) periodic systems as well as their rigorous splitting into atomic electric dipole moments. As examples, Infrared spectra of liquid ethylene carbonate and dimethyl carbonate are presented, which are commonly employed as solvents in Lithium ion batteries.

Evolution of the orbitals Dy-4f in the DyB2 compound using the LDA, PBE approximations, and the PBE0 hybrid functional

NASA Astrophysics Data System (ADS)

Rasero Causil, Diego; Ortega López, César; Espitia Rico, Miguel

2018-04-01

Computational calculations of total energy based on density functional theory were used to investigate the structural, electronic, and magnetic properties of the DyB2 compounds in the hexagonal structure. The calculations were carried out by means of the full-potential linearized augmented plane wave (FP-LAPW) method, employing the computational Wien2k package. The local density approximation (LDA) and the generalized gradient approximation (GGA) were used for the electron-electron interactions. Additionally, we used the functional hybrid PBE0 for a better description the electronic and magnetic properties, because the DyB2 compound is a strongly-correlated system. We found that the calculated lattice constant agrees well with the values reported theoretically and experimentally. The density of states (DOS) calculation shows that the compound exhibits a metallic behavior and has magnetic properties, with a total magnetic moment of 5.47 μ0/cell determined mainly by the 4f states of the rare earth elements. The functional PBE0 shows a strong localization of the Dy-4f orbitals.

What correlation effects are covered by density functional theory?

NASA Astrophysics Data System (ADS)

He, Yuan; Grafenstein, Jurgen; Kraka, Elfi; Cremer, Dieter

The electron density distribution rho(r) generated by a DFT calculation was systematically studied by comparison with a series of reference densities obtained by wavefunction theory (WFT) methods that cover typical electron correlation effects. As a sensitive indicator for correlation effects the dipole moment of the CO molecule was used. The analysis reveals that typical LDA and GGA exchange functionals already simulate effects that are actually reminiscent of pair and three-electron correlation effects covered by MP2, MP4, and CCSD(T) in WFT. Correlation functionals contract the density towards the bond and the valence region thus taking negative charge out of the van der Waals region. It is shown that these improvements are relevant for the description of van der Waals interactions. Similar to certain correlated single-determinant WFT methods, BLYP and other GGA functionals underestimate ionic terms needed for a correct description of polar bonds. This is compensated for in hybrid functionals by mixing in HF exchange. The balanced mixing of local and non-local exchange and correlation effects leads to the correct description of polar bonds as in the B3LYP description of the CO molecule. The density obtained with B3LYP is closer to CCSD and CCSD(T) than to MP2 or MP4, which indicates that the B3LYP hybrid functional mimics those pair and three-electron correlation effects, which in WFT are only covered by coupled cluster methods.

High-density fiber-optic DNA random microsphere array.

PubMed

Ferguson, J A; Steemers, F J; Walt, D R

2000-11-15

A high-density fiber-optic DNA microarray sensor was developed to monitor multiple DNA sequences in parallel. Microarrays were prepared by randomly distributing DNA probe-functionalized 3.1-microm-diameter microspheres in an array of wells etched in a 500-microm-diameter optical imaging fiber. Registration of the microspheres was performed using an optical encoding scheme and a custom-built imaging system. Hybridization was visualized using fluorescent-labeled DNA targets with a detection limit of 10 fM. Hybridization times of seconds are required for nanomolar target concentrations, and analysis is performed in minutes.

Hybrid-exchange density-functional theory study of the electronic structure of MnV2O4 : Exotic orbital ordering in the cubic structure

NASA Astrophysics Data System (ADS)

Wu, Wei

2015-05-01

The electronic structures of cubic and tetragonal MnV2O4 have been studied using hybrid-exchange density-functional theory. The computed electronic structure of the tetragonal phase shows an antiferro-orbital ordering on V sites and a ferrimagnetic ground state (the spins on V and Mn are antialigned). These results are in good agreement with the previous theoretical result obtained from the local-density approximation + U methods [S. Sarkar et al., Phys. Rev. Lett. 102, 216405 (2009), 10.1103/PhysRevLett.102.216405]. Moreover, the electronic structure, especially the projected density of states of the cubic phase, has been predicted with good agreement with the recent soft x-ray spectroscopy experiment. Similar to the tetragonal phase, the spins on V and Mn in the cubic structure favor a ferrimagnetic configuration. Most interesting is that the computed charge densities of the spin-carrying orbitals on V in the cubic phase show an exotic orbital ordering, i.e., a ferro-orbital ordering along [110] but an antiferro-orbital ordering along [1 ¯10 ] .

Density functional theory (DFT) study of a new novel bionanosensor hybrid; tryptophan/Pd doped single walled carbon nanotube

NASA Astrophysics Data System (ADS)

Yoosefian, Mehdi; Etminan, Nazanin

2016-07-01

In order to explore a new novel L-amino acid/transition metal doped single walled carbon nanotube based biosensor, density functional theory calculations were studied. These hybrid structures of organic-inorganic nanobiosensors are able to detect the smallest amino acid building block of proteins. The configurations of amine and carbonyl group coordination of tryptophan aromatic amino acid adsorbed on Pd/doped single walled carbon nanotube were compared. The frontier molecular orbital theory, quantum theory atom in molecule and natural bond orbital analysis were performed. The molecular electrostatic potential and the electron density surfaces were constructed. The calculations indicated that the Pd/SWCNT was sensitive to tryptophan suggesting the importance of interaction with biological molecule and potential detecting application. The proposed nanobiosensor represents a highly sensitive detection of protein at ultra-low concentration in diagnosis applications.

Reference Determinant Dependence of the Random Phase Approximation in 3d Transition Metal Chemistry.

PubMed

Bates, J E; Mezei, P D; Csonka, G I; Sun, J; Ruzsinszky, A

2017-01-10

Without extensive fitting, accurate prediction of transition metal chemistry is a challenge for semilocal and hybrid density funcitonals. The Random Phase Approximation (RPA) has been shown to yield superior results to semilocal functionals for main group thermochemistry, but much less is known about its performance for transition metals. We have therefore analyzed the behavior of reaction energies, barrier heights, and ligand dissociation energies obtained with RPA and compare our results to several semilocal and hybrid functionals. Particular attention is paid to the reference determinant dependence of RPA. We find that typically the results do not vary much between semilocal or hybrid functionals as a reference, as long as the fraction of exact exchange (EXX) mixing in the hybrid functional is small. For large fractions of EXX mixing, however, the Hartree-Fock-like nature of the determinant can severely degrade the performance. Overall, RPA systematically reduces the errors of semilocal functionals and delivers excellent performance from a single reference determinant for inherently multireference reactions. The behavior of dual hybrids that combine RPA correlation with a hybrid exchange energy was also explored, but ultimately did not lead to a systematic improvement compared to traditional RPA for these systems. We rationalize this conclusion by decomposing the contributions to the reaction energies, and briefly discuss the possible implications for double-hybrid functionals based on RPA. The correlation between EXX mixing and spin-symmetry breaking is also discussed.

Long-range corrected density functional through the density matrix expansion based semilocal exchange hole.

PubMed

Patra, Bikash; Jana, Subrata; Samal, Prasanjit

2018-03-28

The exchange hole, which is one of the principal constituents of the density functional formalism, can be used to design accurate range-separated hybrid functionals in association with appropriate correlation. In this regard, the exchange hole derived from the density matrix expansion has gained attention due to its fulfillment of some of the desired exact constraints. Thus, the new long-range corrected density functional proposed here combines the meta generalized gradient approximation level exchange functional designed from the density matrix expansion based exchange hole coupled with the ab initio Hartree-Fock exchange through the range separation of the Coulomb interaction operator using the standard error function technique. Then, in association with the Lee-Yang-Parr correlation functional, the assessment and benchmarking of the above newly constructed range-separated functional with various well-known test sets shows its reasonable performance for a broad range of molecular properties, such as thermochemistry, non-covalent interaction and barrier heights of the chemical reactions.

Tuning TiO2 nanoparticle morphology in graphene-TiO2 hybrids by graphene surface modification

NASA Astrophysics Data System (ADS)

Sordello, Fabrizio; Zeb, Gul; Hu, Kaiwen; Calza, Paola; Minero, Claudio; Szkopek, Thomas; Cerruti, Marta

2014-05-01

We report the hydrothermal synthesis of graphene (GNP)-TiO2 nanoparticle (NP) hybrids using COOH and NH2 functionalized GNP as a shape controller. Anatase was the only TiO2 crystalline phase nucleated on the functionalized GNP, whereas traces of rutile were detected on unfunctionalized GNP. X-Ray Photoelectron spectroscopy (XPS) showed C-Ti bonds on all hybrids, thus confirming heterogeneous nucleation. GNP functionalization induced the nucleation of TiO2 NPs with specific shapes and crystalline facets exposed. COOH functionalization directed the synthesis of anatase truncated bipyramids, bonded to graphene sheets via the {101} facets, while NH2 functionalization induced the formation of belted truncated bipyramids, bonded to graphene via the {100} facets. Belted truncated bipyramids formed on unfunctionalized GNP too, however the NPs were more irregular and rounded. These effects were ascribed to pH variations in the proximity of the functionalized GNP sheets, due to the high density of COOH or NH2 groups. Because of the different reactivity of anatase {100} and {101} crystalline facets, we hypothesize that the hybrid materials will behave differently as photocatalysts, and that the COOH-GNP-TiO2 hybrids will be better photocatalysts for water splitting and H2 production.We report the hydrothermal synthesis of graphene (GNP)-TiO2 nanoparticle (NP) hybrids using COOH and NH2 functionalized GNP as a shape controller. Anatase was the only TiO2 crystalline phase nucleated on the functionalized GNP, whereas traces of rutile were detected on unfunctionalized GNP. X-Ray Photoelectron spectroscopy (XPS) showed C-Ti bonds on all hybrids, thus confirming heterogeneous nucleation. GNP functionalization induced the nucleation of TiO2 NPs with specific shapes and crystalline facets exposed. COOH functionalization directed the synthesis of anatase truncated bipyramids, bonded to graphene sheets via the {101} facets, while NH2 functionalization induced the formation of belted truncated bipyramids, bonded to graphene via the {100} facets. Belted truncated bipyramids formed on unfunctionalized GNP too, however the NPs were more irregular and rounded. These effects were ascribed to pH variations in the proximity of the functionalized GNP sheets, due to the high density of COOH or NH2 groups. Because of the different reactivity of anatase {100} and {101} crystalline facets, we hypothesize that the hybrid materials will behave differently as photocatalysts, and that the COOH-GNP-TiO2 hybrids will be better photocatalysts for water splitting and H2 production. Electronic supplementary information (ESI) available: Statistical analysis of the D : G intensity ratio, additional XPS analysis and TEM micrographs. See DOI: 10.1039/c4nr01322k

Hybrid functional study of band structures of GaAs1-xNx and GaSb1-xNx alloys

NASA Astrophysics Data System (ADS)

Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

2012-02-01

Band structures of GaAs1-xNx and GaSb1-xNx alloys are studied in the framework of the density functional theory within the hybrid functional scheme (HSE06). We find that the scheme gives a clear improvement over the traditional (semi)local functionals in describing, in a qualitative agreement with experiments, the bowing of electron energy band gap in GaAs1-xNx alloys. In the case of GaSb1-xNx alloys, the hybrid functional used makes the study of band structures possible ab initio without any empirical parameter fitting. We explain the trends in the band gap reductions in the two materials that result mainly from the positions of the nitrogen-induced states with respect to the bottoms of the bulk conduction bands.

Performance analysis of boron nitride embedded armchair graphene nanoribbon metal-oxide-semiconductor field effect transistor with Stone Wales defects

NASA Astrophysics Data System (ADS)

Chanana, Anuja; Sengupta, Amretashis; Mahapatra, Santanu

2014-01-01

We study the performance of a hybrid Graphene-Boron Nitride armchair nanoribbon (a-GNR-BN) n-MOSFET at its ballistic transport limit. We consider three geometric configurations 3p, 3p + 1, and 3p + 2 of a-GNR-BN with BN atoms embedded on either side (2, 4, and 6 BN) on the GNR. Material properties like band gap, effective mass, and density of states of these H-passivated structures are evaluated using the Density Functional Theory. Using these material parameters, self-consistent Poisson-Schrodinger simulations are carried out under the Non Equilibrium Green's Function formalism to calculate the ballistic n-MOSFET device characteristics. For a hybrid nanoribbon of width ˜5 nm, the simulated ON current is found to be in the range of 265 μA-280 μA with an ON/OFF ratio 7.1 × 106-7.4 × 106 for a VDD = 0.68 V corresponding to 10 nm technology node. We further study the impact of randomly distributed Stone Wales (SW) defects in these hybrid structures and only 2.5% degradation of ON current is observed for SW defect density of 3.18%.

ωB97X-V: A 10-parameter, range-separated hybrid, generalized gradient approximation density functional with nonlocal correlation, designed by a survival-of-the-fittest strategy

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

Mardirossian, Narbe; Head-Gordon, Martin

2013-12-18

A 10-parameter, range-separated hybrid (RSH), generalized gradient approximation (GGA) density functional with nonlocal correlation (VV10) is presented in this paper. Instead of truncating the B97-type power series inhomogeneity correction factors (ICF) for the exchange, same-spin correlation, and opposite-spin correlation functionals uniformly, all 16 383 combinations of the linear parameters up to fourth order (m = 4) are considered. These functionals are individually fit to a training set and the resulting parameters are validated on a primary test set in order to identify the 3 optimal ICF expansions. Through this procedure, it is discovered that the functional that performs best onmore » the training and primary test sets has 7 linear parameters, with 3 additional nonlinear parameters from range-separation and nonlocal correlation. The resulting density functional, ωB97X-V, is further assessed on a secondary test set, the parallel-displaced coronene dimer, as well as several geometry datasets. Finally and furthermore, the basis set dependence and integration grid sensitivity of ωB97X-V are analyzed and documented in order to facilitate the use of the functional.« less

The nature of three-body interactions in DFT: Exchange and polarization effects

NASA Astrophysics Data System (ADS)

Hapka, Michał; Rajchel, Łukasz; Modrzejewski, Marcin; Schäffer, Rainer; Chałasiński, Grzegorz; Szcześniak, Małgorzata M.

2017-08-01

We propose a physically motivated decomposition of density functional theory (DFT) 3-body nonadditive interaction energies into the exchange and density-deformation (polarization) components. The exchange component represents the effect of the Pauli exclusion in the wave function of the trimer and is found to be challenging for density functional approximations (DFAs). The remaining density-deformation nonadditivity is less dependent upon the DFAs. Numerical demonstration is carried out for rare gas atom trimers, Ar2-HX (X = F, Cl) complexes, and small hydrogen-bonded and van der Waals molecular systems. None of the tested semilocal, hybrid, and range-separated DFAs properly accounts for the nonadditive exchange in dispersion-bonded trimers. By contrast, for hydrogen-bonded systems, range-separated DFAs achieve a qualitative agreement to within 20% of the reference exchange energy. A reliable performance for all systems is obtained only when the monomers interact through the Hartree-Fock potential in the dispersion-free Pauli blockade scheme. Additionally, we identify the nonadditive second-order exchange-dispersion energy as an important but overlooked contribution in force-field-like dispersion corrections. Our results suggest that range-separated functionals do not include this component, although semilocal and global hybrid DFAs appear to imitate it in the short range.

Two-Component Noncollinear Time-Dependent Spin Density Functional Theory for Excited State Calculations.

PubMed

Egidi, Franco; Sun, Shichao; Goings, Joshua J; Scalmani, Giovanni; Frisch, Michael J; Li, Xiaosong

2017-06-13

We present a linear response formalism for the description of the electronic excitations of a noncollinear reference defined via Kohn-Sham spin density functional methods. A set of auxiliary variables, defined using the density and noncollinear magnetization density vector, allows the generalization of spin density functional kernels commonly used in collinear DFT to noncollinear cases, including local density, GGA, meta-GGA and hybrid functionals. Working equations and derivations of functional second derivatives with respect to the noncollinear density, required in the linear response noncollinear TDDFT formalism, are presented in this work. This formalism takes all components of the spin magnetization into account independent of the type of reference state (open or closed shell). As a result, the method introduced here is able to afford a nonzero local xc torque on the spin magnetization while still satisfying the zero-torque theorem globally. The formalism is applied to a few test cases using the variational exact-two-component reference including spin-orbit coupling to illustrate the capabilities of the method.

Density functional theory calculations on transition metal atoms adsorbed on graphene monolayers

NASA Astrophysics Data System (ADS)

Dimakis, Nicholas; Flor, Fernando Antonio; Salgado, Andres; Adjibi, Kolade; Vargas, Sarah; Saenz, Justin

2017-11-01

Transition metal atom adsorption on graphene monolayers has been elucidated using periodic density functional theory under hybrid and generalized gradient approximation functionals. More specifically, we examined the adsorption of Cu, Fe, Zn, Ru, and Os on graphene monolayers by calculating, among others, the electronic density-of-states spectra of the adatom-graphene system and the overlap populations of the adatom with the nearest adsorbing graphene carbon atoms. These calculations reveal that Cu form primarily covalent bonds with graphene atoms via strong hybridization between the adatom orbitals and the sp band of the graphene substrate, whereas the interaction of the Ru and Os with graphene also contain ionic parts. Although the interaction of Fe with graphene atoms is mostly covalent, some charge transfer to graphene is also observed. The interaction of Zn with graphene is weak. Mulliken population analysis and charge contour maps are used to elucidate charge transfers between the adatom and the substrate. The adsorption strength is correlated with the metal adsorption energy and the height of the metal adatom from the graphene plane for the geometrically optimized adatom-graphene system. Our analysis shows that show that metal adsorption strength follows the adatom trend Ru ≈ Os > Fe > Cu > Zn, as verified by corresponding changes in the adsorption energies. The increased metal-carbon orbital overlap for the Ru relative to Os adatom is attributed to hybridization defects.

A density functional theory study of the influence of exchange-correlation functionals on the properties of FeAs.

PubMed

Griffin, Sinéad M; Spaldin, Nicola A

2017-06-01

We use density functional theory within the local density approximation (LDA), LDA  +  U, generalised gradient approximation (GGA), GGA  +  U, and hybrid-functional methods to calculate the properties of iron monoarsenide. FeAs, which forms in the MnP structure, is of current interest for potential spintronic applications as well as being the parent compound for the pnictide superconductors. We compare the calculated structural, magnetic and electronic properties obtained using the different functionals to each other and to experiment, and investigate the origin of a recently reported magnetic spiral. Our results indicate the appropriateness or otherwise of the various functionals for describing FeAs and the related Fe-pnictide superconductors.

Extent of Fock-exchange mixing for a hybrid van der Waals density functional?

NASA Astrophysics Data System (ADS)

Jiao, Yang; Schröder, Elsebeth; Hyldgaard, Per

2018-05-01

The vdW-DF-cx0 exchange-correlation hybrid design [K. Berland et al., J. Chem. Phys. 146, 234106 (2017)] has a truly nonlocal correlation component and aims to facilitate concurrent descriptions of both covalent and non-covalent molecular interactions. The vdW-DF-cx0 design mixes a fixed ratio, a, of the Fock exchange into the consistent-exchange van der Waals density functional, vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B 89, 035412 (2014)]. The mixing value a is sometimes taken as a semi-empirical parameter in hybrid formulations. Here, instead, we assert a plausible optimum average a value for the vdW-DF-cx0 design from a formal analysis; A new, independent determination of the mixing a is necessary since the Becke fit [A. D. Becke, J. Chem. Phys. 98, 5648 (1993)], yielding a' = 0.2, is restricted to semilocal correlation and does not reflect non-covalent interactions. To proceed, we adapt the so-called two-legged hybrid construction [K. Burke et al., Chem. Phys. Lett. 265, 115 (1997)] to a starting point in the vdW-DF-cx functional. For our approach, termed vdW-DF-tlh, we estimate the properties of the adiabatic-connection specification of the exact exchange-correlation functional, by combining calculations of the Fock exchange and of the coupling-constant variation in vdW-DF-cx. We find that such vdW-DF-tlh hybrid constructions yield accurate characterizations of molecular interactions (even if they lack self-consistency). The accuracy motivates trust in the vdW-DF-tlh determination of system-specific values of the Fock-exchange mixing. We find that an average value a' = 0.2 best characterizes the vdW-DF-tlh description of covalent and non-covalent interactions, although there exists some scatter. This finding suggests that the original Becke value, a' = 0.2, also represents an optimal average Fock-exchange mixing for the new, truly nonlocal-correlation hybrids. To enable self-consistent calculations, we furthermore define and test a zero-parameter hybrid functional vdW-DF-cx0p (having fixed mixing a' = 0.2) and document that this truly nonlocal correlation hybrid works for general molecular interactions (at reference and at relaxed geometries). It is encouraging that the vdW-DF-cx0p functional remains useful also for descriptions of some extended systems.

Structural, vibrational, and quasiparticle properties of the Peierls semiconductor BaBiO3 : A hybrid functional and self-consistent GW+vertex-corrections study

NASA Astrophysics Data System (ADS)

Franchini, C.; Sanna, A.; Marsman, M.; Kresse, G.

2010-02-01

BaBiO3 is characterized by a charge disproportionation with half of the Bi atoms possessing a valence 3+ and half a valence 5+ . Because of self-interaction errors, local- and semilocal-density functionals fail to describe the charge disproportionation quantitatively, yielding a too small structural distortion and no band gap. Using hybrid functionals, we obtain a satisfactory description of the structural, electronic, optical, and vibrational properties of BaBiO3 . The results obtained using GW (Green’s function G and screened Coulomb potential W) based schemes on top of hybrid functionals, including fully self-consistent GW calculations with vertex corrections in the dielectric screening, qualitatively confirm the Heyd-Scuseria-Ernzerhof picture but a systematic overestimation of the band gap by about 0.4 eV is observed.

Excitation of lower hybrid waves by a spiraling ion beam in a magnetized dusty plasma cylinder

NASA Astrophysics Data System (ADS)

Sharma, Suresh C.; Walia, Ritu

2008-09-01

A spiraling ion beam propagating through a magnetized dusty plasma cylinder drives electrostatic lower hybrid waves to instability via cyclotron interaction. Numerical calculations of the growth rate and unstable mode frequencies have been carried out for the Princeton Q-1 device using the experimental dusty plasma parameters [e.g., Barkan et al., Planet. Space Sci. 43, 905 (1995)]. It is found that as the density ratio δ(=nio/neo, where ni0 is the ion plasma density and ne0 is the electron density) of negatively charged dust grains to electrons increases, the unstable mode frequency of the lower hybrid waves increases. In addition, the growth rate of the instability also increases with the density ratio δ. In other words, the presence of negatively charged dust grains can further destabilize the lower hybrid wave instability. The growth rate has the largest value for the modes where Jl(pnro) is maximum [here pn=xn/r0, where pn is the perpendicular wave number in cm-1, r0 is the plasma radius, and xn are the zeros of the Bessel function J1(x )] i.e., whose eigenfunctions peak at the location of the beam. The growth rate scales as one third power of the beam current.

Covalent functionalization of graphene by azobenzene with molecular hydrogen bonds for long-term solar thermal storage

NASA Astrophysics Data System (ADS)

Feng, Yiyu; Liu, Hongpo; Luo, Wen; Liu, Enzuo; Zhao, Naiqin; Yoshino, Katsumi; Feng, Wei

2013-11-01

Reduced graphene oxide-azobenzene (RGO-AZO) hybrids were prepared via covalent functionalization for long-term solar thermal storage. Thermal barrier (ΔEa) of cis to tran reversion and thermal storage (ΔH) were improved by molecular hydrogen bonds (H-bonds) through ortho- or para-substitution of AZO. Intramolecular H-bonds thermally stabilized cis-ortho-AZO on RGO with a long-term half-life of 5400 h (ΔEa = 1.2 eV), which was much longer than that of RGO-para-AZO (116 h). RGO-para-AZO with one intermolecular H-bond showed a high density of thermal storage up to 269.8 kJ kg-1 compared with RGO-ortho-AZO (149.6 kJ kg-1) with multiple intra- and intermolecular H-bonds of AZO according to relaxed stable structures. Thermal storage in experiment was the same order magnitude to theoretical data based on ΔH calculated by density functional theory and packing density. Photoactive RGO-AZO hybrid can be developed for high-performance solar thermal storage by optimizing molecular H-bonds.

Covalent functionalization of graphene by azobenzene with molecular hydrogen bonds for long-term solar thermal storage

PubMed Central

Feng, Yiyu; Liu, Hongpo; Luo, Wen; Liu, Enzuo; Zhao, Naiqin; Yoshino, Katsumi; Feng, Wei

2013-01-01

Reduced graphene oxide-azobenzene (RGO-AZO) hybrids were prepared via covalent functionalization for long-term solar thermal storage. Thermal barrier (ΔEa) of cis to tran reversion and thermal storage (ΔH) were improved by molecular hydrogen bonds (H-bonds) through ortho- or para-substitution of AZO. Intramolecular H-bonds thermally stabilized cis-ortho-AZO on RGO with a long-term half-life of 5400 h (ΔEa = 1.2 eV), which was much longer than that of RGO-para-AZO (116 h). RGO-para-AZO with one intermolecular H-bond showed a high density of thermal storage up to 269.8 kJ kg−1 compared with RGO-ortho-AZO (149.6 kJ kg−1) with multiple intra- and intermolecular H-bonds of AZO according to relaxed stable structures. Thermal storage in experiment was the same order magnitude to theoretical data based on ΔH calculated by density functional theory and packing density. Photoactive RGO-AZO hybrid can be developed for high-performance solar thermal storage by optimizing molecular H-bonds. PMID:24247355

Covalent functionalization of graphene by azobenzene with molecular hydrogen bonds for long-term solar thermal storage.

PubMed

Feng, Yiyu; Liu, Hongpo; Luo, Wen; Liu, Enzuo; Zhao, Naiqin; Yoshino, Katsumi; Feng, Wei

2013-11-19

Reduced graphene oxide-azobenzene (RGO-AZO) hybrids were prepared via covalent functionalization for long-term solar thermal storage. Thermal barrier (ΔEa) of cis to tran reversion and thermal storage (ΔH) were improved by molecular hydrogen bonds (H-bonds) through ortho- or para-substitution of AZO. Intramolecular H-bonds thermally stabilized cis-ortho-AZO on RGO with a long-term half-life of 5400 h (ΔEa = 1.2 eV), which was much longer than that of RGO-para-AZO (116 h). RGO-para-AZO with one intermolecular H-bond showed a high density of thermal storage up to 269.8 kJ kg(-1) compared with RGO-ortho-AZO (149.6 kJ kg(-1)) with multiple intra- and intermolecular H-bonds of AZO according to relaxed stable structures. Thermal storage in experiment was the same order magnitude to theoretical data based on ΔH calculated by density functional theory and packing density. Photoactive RGO-AZO hybrid can be developed for high-performance solar thermal storage by optimizing molecular H-bonds.

Hybrid density functional study of bandgaps for 27 new proposed half-Heusler semiconductors

NASA Astrophysics Data System (ADS)

Shi, Fangyi; Si, M. S.; Xie, Jiafeng; Mi, Kui; Xiao, Chuntao; Luo, Qiangjun

2017-12-01

Recently, 27 new half-Heusler compounds XYZ (X = Co, Rh, Fe, Ru, Ni; Y = Sc, Ti, V; Z = P, As, Sb, Si, Ge, Sn, Al, Ga, In) with 18 valence electrons are proposed and their bandgaps span a wide range of 0.10-1.39 eV, which have a great potential of applications in varied areas. Note that the bandgaps are predicted on the gradient-corrected Perdew-Burke-Ernzerhof functional, which underestimates the magnitude of bandgap. To obtain the accurate bandgaps, we recalculate them based on the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. Our results show that the nonlocal correction from the HSE06 functional mainly acts on the two lowest conduction bands. The variation in energy separation between these two bands dominates the relative increment of bandgap. More importantly, the band ordering is distinguished in the presence of HSE06 functional, where the dz2 orbital exhibits. When the lattice constant varies, such a band ordering can be inverted, similar to the case of topological insulators. In addition, we find an abnormal behavior of the bandgap related to the Pauling electronegativity difference between the X- and Z-sites, which arises from the delocalization of charge on the Y-site. We expect that our work can provide guidance to the study of bandgap based on the hybrid density functional theory in the half-Heusler semiconductors.

Charge-transfer channel in quantum dot-graphene hybrid materials

NASA Astrophysics Data System (ADS)

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-01

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd13Se13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Charge-transfer channel in quantum dot-graphene hybrid materials.

PubMed

Cao, Shuo; Wang, Jingang; Ma, Fengcai; Sun, Mengtao

2018-04-06

The energy band theory of a classical semiconductor can qualitatively explain the charge-transfer process in low-dimensional hybrid colloidal quantum dot (QD)-graphene (GR) materials; however, the definite charge-transfer channels are not clear. Using density functional theory (DFT) and time-dependent DFT, we simulate the hybrid QD-GR nanostructure, and by constructing its orbital interaction diagram, we show the quantitative coupling characteristics of the molecular orbitals (MOs) of the hybrid structure. The main MOs are derived from the fragment MOs (FOs) of GR, and the Cd 13 Se 13 QD FOs merge with the GR FOs in a certain proportion to afford the hybrid system. Upon photoexcitation, electrons in the GR FOs jump to the QD FOs, leaving holes in the GR FOs, and the definite charge-transfer channels can be found by analyzing the complex MOs coupling. The excited electrons and remaining holes can also be localized in the GR or the QD or transfer between the QD and GR with different absorption energies. The charge-transfer process for the selected excited states of the hybrid QD-GR structure are testified by the charge difference density isosurface. The natural transition orbitals, charge-transfer length analysis and 2D site representation of the transition density matrix also verify the electron-hole delocalization, localization, or coherence chacracteristics of the selected excited states. Therefore, our research enhances understanding of the coupling mechanism of low-dimensional hybrid materials and will aid in the design and manipulation of hybrid photoelectric devices for practical application in many fields.

Dephasing of LO-phonon-plasmon hybrid modes in n-type GaAs

NASA Astrophysics Data System (ADS)

Vallée, F.; Ganikhanov, F.; Bogani, F.

1997-11-01

The relaxation dynamics of coherent phononlike LO-phonon-plasmon hybrid modes is investigated in n-doped GaAs using an infrared time-resolved coherent anti-Stokes Raman scattering technique. Measurements performed for different crystal temperatures in the range 10-300 K as a function of the electron density injected by doping show a large reduction of the hybrid mode dephasing time compared to the bare LO-phonon one for densities larger than 1016 cm-3. The results are interpreted in terms of coherent decay of the LO-phonon-plasmon mixed mode in the weak-coupling regime and yield information on the plasmon and electron relaxation. The estimated average electron momentum relaxation times are smaller than those deduced from Hall mobility measurements, as expected from our theoretical model.

Compton profiles and electronic properties of TiB{sub 2}

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

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

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

Hybrid particle-continuum simulations coupling Brownian dynamics and local dynamic density functional theory.

PubMed

Qi, Shuanhu; Schmid, Friederike

2017-11-08

We present a multiscale hybrid particle-field scheme for the simulation of relaxation and diffusion behavior of soft condensed matter systems. It combines particle-based Brownian dynamics and field-based local dynamics in an adaptive sense such that particles can switch their level of resolution on the fly. The switching of resolution is controlled by a tuning function which can be chosen at will according to the geometry of the system. As an application, the hybrid scheme is used to study the kinetics of interfacial broadening of a polymer blend, and is validated by comparing the results to the predictions from pure Brownian dynamics and pure local dynamics calculations.

Jacob's Ladder as Sketched by Escher: Assessing the Performance of Broadly Used Density Functionals on Transition Metal Surface Properties.

PubMed

Vega, Lorena; Ruvireta, Judit; Viñes, Francesc; Illas, Francesc

2018-01-09

The present work surveys the performance of various widely used density functional theory exchange-correlation (xc) functionals in describing observable surface properties of a total of 27 transition metals with face-centered cubic (fcc), body-centered cubic (bcc), or hexagonal close-packed (hcp) crystallographic structures. A total of 81 low Miller index surfaces were considered employing slab models. Exemplary xc functionals within the three first rungs of Jacob's ladder were considered, including the Vosko-Wilk-Nusair xc functional within the local density approximation, the Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA), and the Tao-Perdew-Staroverov-Scuseria functional as a meta-GGA functional. Hybrids were excluded in the survey because they are known to fail in properly describing metallic systems. In addition, two variants of PBE were considered, PBE adapted for solids (PBEsol) and revised PBE (RPBE), aimed at improving adsorption energies. Interlayer atomic distances, surface energies, and surface work functions were chosen as the scrutinized properties. A comparison with available experimental data, including single-crystal and polycrystalline values, shows that no xc functional is best at describing all of the surface properties. However, in statistical mean terms the PBEsol xc functional is advised, while PBE is recommended when considering both bulk and surface properties. On the basis of the present results, a discussion of adapting GGA functionals to the treatment of metallic surfaces in an alternative way to meta-GGA or hybrids is provided.

First-principles calculations on the four phases of BaTiO3.

PubMed

Evarestov, Robert A; Bandura, Andrei V

2012-04-30

The calculations based on linear combination of atomic orbitals basis functions as implemented in CRYSTAL09 computer code have been performed for cubic, tetragonal, orthorhombic, and rhombohedral modifications of BaTiO(3) crystal. Structural and electronic properties as well as phonon frequencies were obtained using local density approximation, generalized gradient approximation, and hybrid exchange-correlation density functional theory (DFT) functionals for four stable phases of BaTiO(3). A comparison was made between the results of different DFT techniques. It is concluded that the hybrid PBE0 [J. P. Perdew, K. Burke, M. Ernzerhof, J. Chem. Phys. 1996, 105, 9982.] functional is able to predict correctly the structural stability and phonon properties both for cubic and ferroelectric phases of BaTiO(3). The comparative phonon symmetry analysis in BaTiO(3) four phases has been made basing on the site symmetry and irreducible representation indexes for the first time. Copyright © 2012 Wiley Periodicals, Inc.

Transverse cracking and stiffness reduction in composite laminates

NASA Technical Reports Server (NTRS)

Yuan, F. G.; Selek, M. C.

1993-01-01

A study of transverse cracking mechanism in composite laminates is presented using a singular hybrid finite element model. The model provides the global structural response as well as the precise local crack-tip stress fields. An elasticity basis for the problem is established by employing Lekhnitskii's complex variable potentials and method of eigenfunction expansion. Stress singularities associated with the transverse crack are obtained by decomposing the deformation into the symmetric and antisymmetric modes and proper boundary conditions. A singular hybrid element is thereby formulated based on the variational principle of a modified hybrid functional to incorporate local crack singularities. Axial stiffness reduction due to transverse cracking is studied. The results are shown to be in very good agreement with the existing experimental data. Comparison with simple shear lag analysis is also given. The effects of stress intensity factors and strain energy density on the increase of crack density are analyzed. The results reveal that the parameters approach definite limits when crack densities are saturated, an evidence of the existence of characteristic damage state.

How Well Can Modern Density Functionals Predict Internuclear Distances at Transition States?

PubMed

Xu, Xuefei; Alecu, I M; Truhlar, Donald G

2011-06-14

We introduce a new database called TSG48 containing 48 transition state geometrical data (in particular, internuclear distances in transition state structures) for 16 main group reactions. The 16 reactions are the 12 reactions in the previously published DBH24 database (which includes hydrogen transfer reactions, heavy-atom transfer reactions, nucleophilic substitution reactions, and association reactions plus one unimolecular isomerization) plus four H-transfer reactions in which a hydrogen atom is abstracted by the methyl or hydroperoxyl radical from the two different positions in methanol. The data in TSG48 include data for four reactions that have previously been treated at a very high level in the literature. These data are used to test and validate methods that are affordable for the entire test suite, and the most accurate of these methods is found to be the multilevel BMC-CCSD method. The data that constitute the TSG48 database are therefore taken to consist of these very high level calculations for the four reactions where they are available and BMC-CCSD calculations for the other 12 reactions. The TSG48 database is used to assess the performance of the eight Minnesota density functionals from the M05-M08 families and 26 other high-performance and popular density functionals for locating transition state geometries. For comparison, the MP2 and QCISD wave function methods have also been tested for transition state geometries. The MC3BB and MC3MPW doubly hybrid functionals and the M08-HX and M06-2X hybrid meta-GGAs are found to have the best performance of all of the density functionals tested. M08-HX is the most highly recommended functional due to the excellent performance for all five subsets of TSG48, as well as having a lower cost when compared to doubly hybrid functionals. The mean absolute errors in transition state internuclear distances associated with breaking and forming bonds as calculated by the B2PLYP, MP2, and B3LYP methods are respectively about 2, 3, and 5 times larger than those calculated by MC3BB and M08-HX.

Density functional theory calculations of the water interactions with ZrO2 nanoparticles Y2O3 doped

NASA Astrophysics Data System (ADS)

Subhoni, Mekhrdod; Kholmurodov, Kholmirzo; Doroshkevich, Aleksandr; Asgerov, Elmar; Yamamoto, Tomoyuki; Lyubchyk, Andrei; Almasan, Valer; Madadzada, Afag

2018-03-01

Development of a new electricity generation techniques is one of the most relevant tasks, especially nowadays under conditions of extreme growth in energy consumption. The exothermic heterogeneous electrochemical energy conversion to the electric energy through interaction of the ZrO2 based nanopowder system with atmospheric moisture is one of the ways of electric energy obtaining. The questions of conversion into the electric form of the energy of water molecules adsorption in 3 mol% Y2O3 doped ZrO2 nanopowder systems were investigated using the density functional theory calculations. The density functional theory calculations has been realized as in the Kohn-Sham formulation, where the exchange-correlation potential is approximated by a functional of the electronic density. The electronic density, total energy and band structure calculations are carried out using the all-electron, full potential, linear augmented plane wave method of the electronic density and related approximations, i.e. the local density, the generalized gradient and their hybrid approximations.

Hybrid functional study of α-uranium

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

Kaur, Gurpreet, E-mail: gurpreet@igcar.gov.in; Chinnappan, Ravi; Panigrahi, B. K.

2016-05-23

We have used the hybrid density functionals to study the structural and electronic properties of alpha-U. The fraction of exact Hartree Folk exchange used is varied from 0.0 to 0.6. The equilibrium volume is found to be underestimated and bulk modulus overestimated with HSE as compared to both calculated by PBE and the experimental values. Electronic bands below the Fermi level are found to shift to lower energy with respect to PBE electronic bands which itself gives the bands shifted to lower energies as compared to UPS experiments.

Electronic Structure Approach to Tunable Electronic Properties of Hybrid Organic-Inorganic Perovskites

NASA Astrophysics Data System (ADS)

Liu, Garnett; Huhn, William; Mitzi, David B.; Kanai, Yosuke; Blum, Volker

We present a study of the electronic structure of layered hybrid organic-inorganic perovskite (HOIP) materials using all-electron density-functional theory. Varying the nature of the organic and inorganic layers should enable systematically fine-tuning the carrier properties of each component. Using the HSE06 hybrid density functional including spin-orbit coupling (SOC), we validate the principle of tuning subsystem-specific parts of the electron band structures and densities of states in CH3NH3PbX3 (X=Cl, Br, I) compared to a modified organic component in layered (C6H5C2H4NH3) 2PbX4 (X=Cl, Br, I) and C20H22S4N2PbX4 (X=Cl, Br, I). We show that tunable shifts of electronic levels indeed arise by varying Cl, Br, I as the inorganic components, and CH3NH3+ , C6H5C2H4NH3+ , C20H22S4N22 + as the organic components. SOC is found to play an important role in splitting the conduction bands of the HOIP compounds investigated here. The frontier orbitals of the halide shift, increasing the gap, when Cl is substituted for Br and I.

Performance analysis of boron nitride embedded armchair graphene nanoribbon metal–oxide–semiconductor field effect transistor with Stone Wales defects

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

Chanana, Anuja; Sengupta, Amretashis; Mahapatra, Santanu

2014-01-21

We study the performance of a hybrid Graphene-Boron Nitride armchair nanoribbon (a-GNR-BN) n-MOSFET at its ballistic transport limit. We consider three geometric configurations 3p, 3p + 1, and 3p + 2 of a-GNR-BN with BN atoms embedded on either side (2, 4, and 6 BN) on the GNR. Material properties like band gap, effective mass, and density of states of these H-passivated structures are evaluated using the Density Functional Theory. Using these material parameters, self-consistent Poisson-Schrodinger simulations are carried out under the Non Equilibrium Green's Function formalism to calculate the ballistic n-MOSFET device characteristics. For a hybrid nanoribbon of widthmore » ∼5 nm, the simulated ON current is found to be in the range of 265 μA–280 μA with an ON/OFF ratio 7.1 × 10{sup 6}–7.4 × 10{sup 6} for a V{sub DD} = 0.68 V corresponding to 10 nm technology node. We further study the impact of randomly distributed Stone Wales (SW) defects in these hybrid structures and only 2.5% degradation of ON current is observed for SW defect density of 3.18%.« less

On the feasibility of p-type Ga2O3

NASA Astrophysics Data System (ADS)

Kyrtsos, Alexandros; Matsubara, Masahiko; Bellotti, Enrico

2018-01-01

We investigate the various cation substitutional dopants in Ga2O3 for the possibility of p-type conductivity using density functional theory. Our calculations include both standard density functional theory and hybrid functional calculations. We demonstrate that all the investigated dopants result in deep acceptor levels, not able to contribute to the p-type conductivity of Ga2O3. In light of these results, we compare our findings with other wide bandgap oxides and reexamine previous experiments on zinc doping in Ga2O3.

Validation of electronic structure methods for isomerization reactions of large organic molecules.

PubMed

Luo, Sijie; Zhao, Yan; Truhlar, Donald G

2011-08-14

In this work the ISOL24 database of isomerization energies of large organic molecules presented by Huenerbein et al. [Phys. Chem. Chem. Phys., 2010, 12, 6940] is updated, resulting in the new benchmark database called ISOL24/11, and this database is used to test 50 electronic model chemistries. To accomplish the update, the very expensive and highly accurate CCSD(T)-F12a/aug-cc-pVDZ method is first exploited to investigate a six-reaction subset of the 24 reactions, and by comparison of various methods with the benchmark, MCQCISD-MPW is confirmed to be of high accuracy. The final ISOL24/11 database is composed of six reaction energies calculated by CCSD(T)-F12a/aug-cc-pVDZ and 18 calculated by MCQCISD-MPW. We then tested 40 single-component density functionals (both local and hybrid), eight doubly hybrid functionals, and two other methods against ISOL24/11. It is found that the SCS-MP3/CBS method, which is used as benchmark for the original ISOL24, has an MUE of 1.68 kcal mol(-1), which is close to or larger than some of the best tested DFT methods. Using the new benchmark, we find ωB97X-D and MC3MPWB to be the best single-component and doubly hybrid functionals respectively, with PBE0-D3 and MC3MPW performing almost as well. The best single-component density functionals without molecular mechanics dispersion-like terms are M08-SO, M08-HX, M05-2X, and M06-2X. The best single-component density functionals without Hartree-Fock exchange are M06-L-D3 when MM terms are included and M06-L when they are not.

First-principles study of the stability, magnetic and electronic properties of Fe and Co monoatomic chains encapsulated into copper nanotube

NASA Astrophysics Data System (ADS)

Ma, Liang-Cai; Ma, Ling; Zhang, Jian-Min

2017-07-01

By using first-principles calculations based on density-functional theory, the stability, magnetic and electronic properties of Fe and Co monoatomic chains encapsulated into copper nanotube are systematically investigated. The binding energies of the hybrid structures are remarkably higher than those of corresponding freestanding TM chains, indicating the TM chains are significantly stabilized after encapsulating into copper nanotube. The formed bonds between outer Cu and inner TM atoms show some degree of covalent bonding character. The magnetic ground states of Fe@CuNW and Co@CuNW hybrid structures are ferromagnetic, and both spin and orbital magnetic moments of inner TM atoms have been calculated. The magnetocrystalline anisotropy energies (MAE) of the hybrid structures are enhanced by nearly fourfold compared to those of corresponding freestanding TM chains, indicating that the hybrid structures can be used in ultrahigh density magnetic storage. Furthermore, the easy magnetization axis switches from that along the axis in freestanding Fe chain to that perpendicular to the axis in Fe@CuNT hybrid structure. The large spin polarization at the Fermi level also makes the hybrid systems interesting as good potential materials for spintronic devices.

A functional hybrid memristor crossbar-array/CMOS system for data storage and neuromorphic applications.

PubMed

Kim, Kuk-Hwan; Gaba, Siddharth; Wheeler, Dana; Cruz-Albrecht, Jose M; Hussain, Tahir; Srinivasa, Narayan; Lu, Wei

2012-01-11

Crossbar arrays based on two-terminal resistive switches have been proposed as a leading candidate for future memory and logic applications. Here we demonstrate a high-density, fully operational hybrid crossbar/CMOS system composed of a transistor- and diode-less memristor crossbar array vertically integrated on top of a CMOS chip by taking advantage of the intrinsic nonlinear characteristics of the memristor element. The hybrid crossbar/CMOS system can reliably store complex binary and multilevel 1600 pixel bitmap images using a new programming scheme. © 2011 American Chemical Society

Quadratic integrand double-hybrid made spin-component-scaled

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

Brémond, Éric, E-mail: eric.bremond@iit.it; Savarese, Marika; Sancho-García, Juan C.

2016-03-28

We propose two analytical expressions aiming to rationalize the spin-component-scaled (SCS) and spin-opposite-scaled (SOS) schemes for double-hybrid exchange-correlation density-functionals. Their performances are extensively tested within the framework of the nonempirical quadratic integrand double-hybrid (QIDH) model on energetic properties included into the very large GMTKN30 benchmark database, and on structural properties of semirigid medium-sized organic compounds. The SOS variant is revealed as a less computationally demanding alternative to reach the accuracy of the original QIDH model without losing any theoretical background.

Four-Component Relativistic Density-Functional Theory Calculations of Nuclear Spin-Rotation Constants: Relativistic Effects in p-Block Hydrides.

PubMed

Komorovsky, Stanislav; Repisky, Michal; Malkin, Elena; Demissie, Taye B; Ruud, Kenneth

2015-08-11

We present an implementation of the nuclear spin-rotation (SR) constants based on the relativistic four-component Dirac-Coulomb Hamiltonian. This formalism has been implemented in the framework of the Hartree-Fock and Kohn-Sham theory, allowing assessment of both pure and hybrid exchange-correlation functionals. In the density-functional theory (DFT) implementation of the response equations, a noncollinear generalized gradient approximation (GGA) has been used. The present approach enforces a restricted kinetic balance condition for the small-component basis at the integral level, leading to very efficient calculations of the property. We apply the methodology to study relativistic effects on the spin-rotation constants by performing calculations on XHn (n = 1-4) for all elements X in the p-block of the periodic table and comparing the effects of relativity on the nuclear SR tensors to that observed for the nuclear magnetic shielding tensors. Correlation effects as described by the density-functional theory are shown to be significant for the spin-rotation constants, whereas the differences between the use of GGA and hybrid density functionals are much smaller. Our calculated relativistic spin-rotation constants at the DFT level of theory are only in fair agreement with available experimental data. It is shown that the scaling of the relativistic effects for the spin-rotation constants (varying between Z(3.8) and Z(4.5)) is as strong as for the chemical shieldings but with a much smaller prefactor.

Four- and eight-membered rings carbon nanotubes: A new class of carbon nanomaterials

NASA Astrophysics Data System (ADS)

Li, Fangfang; Lu, Junzhe; Zhu, Hengjiang; Lin, Xiang

2018-06-01

A new class of carbon nanomaterials composed of alternating four- and eight-membered rings is studied by density functional theory (DFT), including single-walled carbon nanotubes (SWCNTs) double-walled carbon nanotubes (DWCNTs) and triple-walled CNTs (TWCNTs). The analysis of geometrical structure shows that carbon atoms' hybridization in novel carbon tubular clusters (CTCs) and the corresponding carbon nanotubes (CNTs) are both sp2 hybridization; The thermal properties exhibit the high stability of these new CTCs. The results of energy band and density of state (DOS) indicate that the electronic properties of CNTs are independent of their diameter, number of walls and chirality, exhibit obvious metal properties.

Laser Scribed Graphene Cathode for Next Generation of High Performance Hybrid Supercapacitors.

PubMed

Lee, Seung-Hwan; Kim, Jin Hyeon; Yoon, Jung-Rag

2018-05-25

Hybrid supercapacitors have been regarded as next-generation energy storage devices due to their outstanding performances. However, hybrid supercapacitors remain a great challenge to enhance the energy density of hybrid supercapacitors. Herein, a novel approach for high-energy density hybrid supercapacitors based on a laser scribed graphene cathode and AlPO 4 -carbon hybrid coated H 2 Ti 12 O 25 (LSG/H-HTO) was designed. Benefiting from high-energy laser scribed graphene and high-power H-HTO, it was demonstrated that LSG/H-HTO delivers superior energy and power densities with excellent cyclability. Compared to previous reports on other hybrid supercapacitors, LSG/H-HTO electrode composition shows extraordinary energy densities of ~70.8 Wh/kg and power densities of ~5191.9 W/kg. Therefore, LSG/H-HTO can be regarded as a promising milestone in hybrid supercapacitors.

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

NASA Astrophysics Data System (ADS)

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

2018-01-01

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

N-Doped Hybrid Graphene and Boron Nitride Armchair Nanoribbons As Nonmagnetic Semiconductors with Widely Tunable Electronic Properties

NASA Astrophysics Data System (ADS)

Habibpour, Razieh; Kashi, Eslam; Vazirib, Raheleh

2018-03-01

The electronic and chemical properties of N-doped hybrid graphene and boron nitride armchair nanoribbons (N-doped a-GBNNRs) in comparison with graphene armchair nanoribbon (pristine a-GNR) and hybrid graphene and boron nitride armchair nanoribbon (C-3BN) are investigated using the density functional theory method. The results show that all the mentioned nanoribbons are nonmagnetic direct semiconductors and all the graphitic N-doped a-GBNNRs are n-type semiconductors while the rest are p-type semiconductors. The N-doped graphitic 2 and N-doped graphitic 3 structures have the lowest work function and the highest number of valence electrons (Lowdin charges) which confirms that they are effective for use in electronic device applications.

Lower hybrid wave phenomena associated with density depletions

NASA Technical Reports Server (NTRS)

Seyler, C. E.

1994-01-01

A fluid description of lower hybrid, whistler and magnetosonic waves is applied to study wave phenomena near the lower hybrid resonance associated with plasma density depletions. The goal is to understand the nature of lower hybrid cavitons and spikelets often associated with transverse ion acceleration events in the auroral ionosphere. Three-dimensional simulations show the ponderomotive force leads to the formation of a density cavity (caviton) in which lower hybrid wave energy is concentrated (spikelet) resulting in a three-dimensional collapse of the configuration. Plasma density depletions of the order of a few percent are shown to greatly modify the homogeneous linear properties of lower hybrid waves and account for many of the observed features of lower hybrid spikelets.

A hybrid method for solutes in complex solvents: Density functional theory combined with empirical force fields

NASA Astrophysics Data System (ADS)

Eichinger, M.; Tavan, P.; Hutter, J.; Parrinello, M.

1999-06-01

We present a hybrid method for molecular dynamics simulations of solutes in complex solvents as represented, for example, by substrates within enzymes. The method combines a quantum mechanical (QM) description of the solute with a molecular mechanics (MM) approach for the solvent. The QM fragment of a simulation system is treated by ab initio density functional theory (DFT) based on plane-wave expansions. Long-range Coulomb interactions within the MM fragment and between the QM and the MM fragment are treated by a computationally efficient fast multipole method. For the description of covalent bonds between the two fragments, we introduce the scaled position link atom method (SPLAM), which removes the shortcomings of related procedures. The various aspects of the hybrid method are scrutinized through test calculations on liquid water, the water dimer, ethane and a small molecule related to the retinal Schiff base. In particular, the extent to which vibrational spectra obtained by DFT for the solute can be spoiled by the lower quality force field of the solvent is checked, including cases in which the two fragments are covalently joined. The results demonstrate that our QM/MM hybrid method is especially well suited for the vibrational analysis of molecules in condensed phase.

Planar n-Si/PEDOT:PSS hybrid heterojunction solar cells utilizing functionalized carbon nanoparticles synthesized via simple pyrolysis route

NASA Astrophysics Data System (ADS)

Nam, Yoon-Ho; Kim, Dong-Hyung; Shinde, Sambhaji S.; Song, Jae-Won; Park, Min-Joon; Yu, Jin-Young; Lee, Jung-Ho

2017-11-01

Herein, we present a facile and simple strategy for in situ synthesis of functionalized carbon nanoparticles (CNPs) via direct pyrolysis of ethylenediaminetetraacetic acid (EDTA) on silicon surface. The CNPs were incorporated in hybrid planar n-Si and poly(3,4-etyhlenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells to improve device performance. We demonstrate that the CNPs-incorporated devices showed increased electrical conductivity (reduced series resistance) and minority carrier lifetime (better charge carrier collection) than those of the cells without CNPs due to the existence of electrically conductive sp 2-hybridized carbon at the heterojunction interfaces. With an optimal concentration of CNPs, the hybrid solar cells exhibited power conversion efficiency up to 11.95%, with an open-circuit voltage of 614 mV, short-circuit current density of 26.34 mA cm-2, and fill factor of 73.93%. These results indicate that our approach is promising for the development of highly efficient organic-inorganic hybrid solar cells.

Electron density and temperature in an atmospheric-pressure helium diffuse dielectric barrier discharge from kHz to MHz

NASA Astrophysics Data System (ADS)

Boisvert, J.-S.; Stafford, L.; Naudé, N.; Margot, J.; Massines, F.

2018-03-01

Diffuse dielectric barrier discharges are generated over a very wide range of frequencies. According to the targeted frequency, the glow, Townsend-like, hybrid, Ω and RF-α modes are sustained. In this paper, the electrical characterization of the discharge cell together with an electrical model are used to estimate the electron density from current and voltage measurements for excitation frequencies ranging from 50 kHz to 15 MHz. The electron density is found to vary from 1014 to 1017 m-3 over this frequency range. In addition, a collisional-radiative model coupled with optical emission spectroscopy is used to evaluate the electron temperature (assuming Maxwellian electron energy distribution function) in the same conditions. The time and space-averaged electron temperature is found to be about 0.3 eV in both the low-frequency and high-frequency ranges. However, in the medium-frequency range, it reaches almost twice this value as the discharge is in the hybrid mode. The hybrid mode is similar to the atmospheric-pressure glow discharge usually observed in helium DBDs at low frequency with the major difference being that the plasma is continuously sustained and is characterized by a higher power density.

An inorganic/organic hybrid magnetic network as a colorimetric fluorescent nanosensor and its recognizing behavior toward Hg2+

NASA Astrophysics Data System (ADS)

Zeng, Xianfei; Xu, Yaohui; Chen, Xiumin; Ma, Wenhui; Zhou, Yang

2017-11-01

An inorganic/organic hybrid magnetic Fe3O4@SiO2 network functionalized with rhodamine derivatives was devised as a nanosensor for selective detection and removal of Hg2+ in this work. The inorganic/organic hybrid composites showed naked-eye color change in water/methanol media. The distinct color change on the surface of functionalized composite network was observed by separating and drying from aqueous solution after adsorbing Hg2+. The fluorescence spectra indicated that the functionalized nanosensor was highly sensitive and selective to Hg2+ in aqueous solution. Density functional theory (DFT) calculation was performed, which revealed a mechanism of fluorescence generated from Hg2+ induced desulfurization of rhodamine derivatives via forming new five-membered ring structure. The as-obtained composites not only had an excellent adsorption capability for Hg2+, but also showed a strong magnetic sensitivity, which allowed one to separate the functionalized magnetic nanocomposites from the solution.

Density functional theory study of defects in unalloyed δ-Pu

DOE PAGES

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

2017-03-19

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Density functional theory study of defects in unalloyed δ-Pu

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

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Rare earth substitutional impurities in germanium: A hybrid density functional theory study

NASA Astrophysics Data System (ADS)

Igumbor, E.; Omotoso, E.; Tunhuma, S. M.; Danga, H. T.; Meyer, W. E.

2017-10-01

The Heyd, Scuseria, and Ernzerhof (HSE06) hybrid functional by means of density functional theory has been used to model the electronic and structural properties of rare earth (RE) substitutional impurities in germanium (REGe) . The formation and charge state transition energies for the REGe (RE = Ce, Pr, Er and Eu) were calculated. The energy of formation for the neutral charge state of the REGe lies between -0.14 and 3.13 eV. The formation energy result shows that the Pr dopant in Ge (PrGe) has the lowest formation energy of -0.14 eV, and is most energetically favourable under equilibrium conditions. The REGe induced charge state transition levels within the band gap of Ge. Shallow acceptor levels were induced by both the Eu (EuGe) and Pr (PrGe) dopants in Ge. The CeGe and ErGe exhibited properties of negative-U ordering with effective-U values of -0.85 and -1.07 eV, respectively.

Intrinsic point defects in β-In2S3 studied by means of hybrid density-functional theory

NASA Astrophysics Data System (ADS)

Ghorbani, Elaheh; Albe, Karsten

2018-03-01

We have employed first principles total energy calculations in the framework of density functional theory, with plane wave basis sets and screened exchange hybrid functionals to study the incorporation of intrinsic defects in bulk β-In2S3. The results are obtained for In-rich and S-rich experimental growth conditions. The charge transition level is discussed for all native defects, including VIn, VS, Ini, Si, SIn, and InS, and a comparison between the theoretically calculated charge transition levels and the available experimental findings is presented. The results imply that β-In2S3 shows n-type conductivity under both In-rich and S-rich growth conditions. The indium antiisite (InS), the indium interstitial (Ini), and the sulfur vacancy ( VS ' ) are found to be the leading sources of sample's n-type conductivity. When going from the In-rich to the S-rich condition, the conductivity of the material decreases; however, the type of conductivity remains unchanged.

Hybrid asymptotic-numerical approach for estimating first-passage-time densities of the two-dimensional narrow capture problem.

PubMed

Lindsay, A E; Spoonmore, R T; Tzou, J C

2016-10-01

A hybrid asymptotic-numerical method is presented for obtaining an asymptotic estimate for the full probability distribution of capture times of a random walker by multiple small traps located inside a bounded two-dimensional domain with a reflecting boundary. As motivation for this study, we calculate the variance in the capture time of a random walker by a single interior trap and determine this quantity to be comparable in magnitude to the mean. This implies that the mean is not necessarily reflective of typical capture times and that the full density must be determined. To solve the underlying diffusion equation, the method of Laplace transforms is used to obtain an elliptic problem of modified Helmholtz type. In the limit of vanishing trap sizes, each trap is represented as a Dirac point source that permits the solution of the transform equation to be represented as a superposition of Helmholtz Green's functions. Using this solution, we construct asymptotic short-time solutions of the first-passage-time density, which captures peaks associated with rapid capture by the absorbing traps. When numerical evaluation of the Helmholtz Green's function is employed followed by numerical inversion of the Laplace transform, the method reproduces the density for larger times. We demonstrate the accuracy of our solution technique with a comparison to statistics obtained from a time-dependent solution of the diffusion equation and discrete particle simulations. In particular, we demonstrate that the method is capable of capturing the multimodal behavior in the capture time density that arises when the traps are strategically arranged. The hybrid method presented can be applied to scenarios involving both arbitrary domains and trap shapes.

Magnetic exchange couplings from noncollinear perturbation theory: dinuclear CuII complexes.

PubMed

Phillips, Jordan J; Peralta, Juan E

2014-08-07

To benchmark the performance of a new method based on noncollinear coupled-perturbed density functional theory [J. Chem. Phys. 138, 174115 (2013)], we calculate the magnetic exchange couplings in a series of triply bridged ferromagnetic dinuclear Cu(II) complexes that have been recently synthesized [Phys. Chem. Chem. Phys. 15, 1966 (2013)]. We find that for any basis-set the couplings from our noncollinear coupled-perturbed methodology are practically identical to those of spin-projected energy-differences when a hybrid density functional approximation is employed. This demonstrates that our methodology properly recovers a Heisenberg description for these systems, and is robust in its predictive power of magnetic couplings. Furthermore, this indicates that the failure of density functional theory to capture the subtle variation of the exchange couplings in these complexes is not simply an artifact of broken-symmetry methods, but rather a fundamental weakness of current approximate density functionals for the description of magnetic couplings.

Control of DNA-Functionalized Nanoparticle Assembly

NASA Astrophysics Data System (ADS)

Olvera de La Cruz, Monica

Directed crystallization of a large variety of nanoparticles, including proteins, via DNA hybridization kinetics has led to unique materials with a broad range of crystal symmetries. The nanoparticles are functionalized with DNA chains that link neighboring functionalized units. The shape of the nanoparticle, the DNA length, the sequence of the hybridizing DNA linker and the grafting density determine the crystal symmetries and lattice spacing. By carefully selecting these parameters one can, in principle, achieve all the symmetries found for both atomic and colloidal crystals of asymmetric shapes as well as new symmetries, and drive transitions between them. A scale-accurate coarse-grained model with explicit DNA chains provides the design parameters, including degree of hybridization, to achieve specific crystal structures. The model also provides surface energy values to determine the shape of defect-free single crystals with macroscopic anisotropic properties, as well as the parameters to develop colloidal models that reproduce both the shape of single crystals and their growth kinetics.

Design, processing and testing of LSI arrays hybrid microelectronics task

NASA Technical Reports Server (NTRS)

Himmel, R. P.; Stuhlbarg, S. M.; Salmassy, S.

1978-01-01

Those factors affecting the cost of electronic subsystems utilizing LSI microcircuits were determined and the most efficient methods for low cost packaging of LSI devices as a function of density and reliability were developed.

Density Functional Theory Study of Leaching Performance of Different Acids on Pyrochlore (100) Surface

NASA Astrophysics Data System (ADS)

Yang, Xiuli; Fang, Qing; Ouyang, Hui

2018-04-01

Pyrochlore leaching using hydrofluoric, sulfuric, and hydrochloric acids has been studied via experimental methods for years, but the interactions between niobium atoms on the pyrochlore surface and different acids have not been investigated. In this work, first-principles calculations based on density functional theory were used to elucidate the leaching performance of these three acids from the viewpoint of geometrical and electronic structures. The calculation results indicate that sulfate, chloride, and fluoride anions influence the geometric structure of pyrochlore (100) to different extents, decreasing in the order: sulfate, fluoride, chloride. Orbitals of O1 and O2 atoms of sulfate hybridized with those of surface niobium atom. Fluorine orbitals hybridized with those of surface niobium atoms. However, no obvious overlap exists between any orbitals of chlorine and surface niobium, revealing that chlorine does not interact chemically with surface niobium atoms.

Density Functional Theory Study of Leaching Performance of Different Acids on Pyrochlore (100) Surface

NASA Astrophysics Data System (ADS)

Yang, Xiuli; Fang, Qing; Ouyang, Hui

2018-06-01

Pyrochlore leaching using hydrofluoric, sulfuric, and hydrochloric acids has been studied via experimental methods for years, but the interactions between niobium atoms on the pyrochlore surface and different acids have not been investigated. In this work, first-principles calculations based on density functional theory were used to elucidate the leaching performance of these three acids from the viewpoint of geometrical and electronic structures. The calculation results indicate that sulfate, chloride, and fluoride anions influence the geometric structure of pyrochlore (100) to different extents, decreasing in the order: sulfate, fluoride, chloride. Orbitals of O1 and O2 atoms of sulfate hybridized with those of surface niobium atom. Fluorine orbitals hybridized with those of surface niobium atoms. However, no obvious overlap exists between any orbitals of chlorine and surface niobium, revealing that chlorine does not interact chemically with surface niobium atoms.

A Hybrid Density Functional Study of Atomic Hydrogen and Oxygen Adsorptions on the (0001) Surface of Non-Magnetic DHCP Americium

NASA Astrophysics Data System (ADS)

Amdani-Moten, Shafaq; Atta-Fynn, Raymond; Ray, Asok

2010-03-01

As our group have recently shown^+, hybrid density functional theory (HDFT) which replaces a fraction (40%) of approximate DFT exchange with exact Hartree-Fock exchange yield structural, magnetic, and electronic properties for Americium-I that are in excellent agreement with experimental data. As a natural progression, ab initio calculations for atomic adsorptions on the (0001) surface of non-magnetic americium have been performed using HDFT. The americium surface is modeled by a seven-layer slab using inversion symmetry consisting of one atom per layer and non-magnetic ABAC stacking arrangement of these layers. Top, bridge, hcp and fcc chemisorption sites have been investigated with energies optimized with respect to the adatom distance from the surface. Details of the chemisorptions processes as well as comparisons of different sites will be presented. ^+ R. Atta-Fynn and A. K. Ray, Chemical Physics Letters, 482, 223-227 (2009).

A Well-Tempered Hybrid Method for Solving Challenging Time-Dependent Density Functional Theory (TDDFT) Systems.

PubMed

Kasper, Joseph M; Williams-Young, David B; Vecharynski, Eugene; Yang, Chao; Li, Xiaosong

2018-04-10

The time-dependent Hartree-Fock (TDHF) and time-dependent density functional theory (TDDFT) equations allow one to probe electronic resonances of a system quickly and inexpensively. However, the iterative solution of the eigenvalue problem can be challenging or impossible to converge, using standard methods such as the Davidson algorithm for spectrally dense regions in the interior of the spectrum, as are common in X-ray absorption spectroscopy (XAS). More robust solvers, such as the generalized preconditioned locally harmonic residual (GPLHR) method, can alleviate this problem, but at the expense of higher average computational cost. A hybrid method is proposed which adapts to the problem in order to maximize computational performance while providing the superior convergence of GPLHR. In addition, a modification to the GPLHR algorithm is proposed to adaptively choose the shift parameter to enforce a convergence of states above a predefined energy threshold.

Optimized Vertex Method and Hybrid Reliability

NASA Technical Reports Server (NTRS)

Smith, Steven A.; Krishnamurthy, T.; Mason, B. H.

2002-01-01

A method of calculating the fuzzy response of a system is presented. This method, called the Optimized Vertex Method (OVM), is based upon the vertex method but requires considerably fewer function evaluations. The method is demonstrated by calculating the response membership function of strain-energy release rate for a bonded joint with a crack. The possibility of failure of the bonded joint was determined over a range of loads. After completing the possibilistic analysis, the possibilistic (fuzzy) membership functions were transformed to probability density functions and the probability of failure of the bonded joint was calculated. This approach is called a possibility-based hybrid reliability assessment. The possibility and probability of failure are presented and compared to a Monte Carlo Simulation (MCS) of the bonded joint.

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.

Determination of ionospheric electron density profiles from satellite UV (Ultraviolet) emission measurements, fiscal year 1984

NASA Astrophysics Data System (ADS)

Daniell, R. E.; Strickland, D. J.; Decker, D. T.; Jasperse, J. R.; Carlson, H. C., Jr.

1985-04-01

The possible use of satellite ultraviolet measurements to deduce the ionospheric electron density profile (EDP) on a global basis is discussed. During 1984 comparisons were continued between the hybrid daytime ionospheric model and the experimental observations. These comparison studies indicate that: (1) the essential features of the EDP and certain UV emissions can be modelled; (2) the models are sufficiently sensitive to input parameters to yield poor agreement with observations when typical input values are used; (3) reasonable adjustments of the parameters can produce excellent agreement between theory and data for either EDP or airglow but not both; and (4) the qualitative understanding of the relationship between two input parameters (solar flux and neutral densities) and the model EDP and airglow features has been verified. The development of a hybrid dynamic model for the nighttime midlatitude ionosphere has been initiated. This model is similar to the daytime hybrid model, but uses the sunset EDP as an initial value and calculates the EDP as a function of time through the night. In addition, a semiempirical model has been developed, based on the assumption that the nighttime EDP is always well described by a modified Chapman function. This model has great simplicity and allows the EDP to be inferred in a straightforward manner from optical observations. Comparisons with data are difficult, however, because of the low intensity of the nightglow.

An extended hybrid density functional (X3LYP) with improved descriptions of nonbond interactions and thermodynamic properties of molecular systems

NASA Astrophysics Data System (ADS)

Xu, Xin; Zhang, Qingsong; Muller, Richard P.; Goddard, William A.

2005-01-01

We derive here the form for the exact exchange energy density for a density that decays with Gaussian-type behavior at long range. This functional is intermediate between the B88 and the PW91 exchange functionals. Using this modified functional to match the form expected for Gaussian densities, we propose the X3LYP extended functional. We find that X3LYP significantly outperforms Becke three parameter Lee-Yang-Parr (B3LYP) for describing van der Waals and hydrogen bond interactions, while performing slightly better than B3LYP for predicting heats of formation, ionization potentials, electron affinities, proton affinities, and total atomic energies as validated with the extended G2 set of atoms and molecules. Thus X3LYP greatly enlarges the field of applications for density functional theory. In particular the success of X3LYP in describing the water dimer (with Re and De within the error bars of the most accurate determinations) makes it an excellent candidate for predicting accurate ligand-protein and ligand-DNA interactions.

Use of the interior cavity of the P22 capsid for site-specific initiation of atom-transfer radical polymerization with high-density cargo loading

NASA Astrophysics Data System (ADS)

Lucon, Janice; Qazi, Shefah; Uchida, Masaki; Bedwell, Gregory J.; Lafrance, Ben; Prevelige, Peter E.; Douglas, Trevor

2012-10-01

Virus-like particles (VLPs) have emerged as important and versatile architectures for chemical manipulation in the development of functional hybrid nanostructures. Here we demonstrate a successful site-selective initiation of atom-transfer radical polymerization reactions to form an addressable polymer constrained within the interior cavity of a VLP. Potentially, this protein-polymer hybrid of P22 and cross-linked poly(2-aminoethyl methacrylate) could be useful as a new high-density delivery vehicle for the encapsulation and delivery of small-molecule cargos. In particular, the encapsulated polymer can act as a scaffold for the attachment of small functional molecules, such as fluorescein dye or the magnetic resonance imaging (MRI) contrast agent Gd-diethylenetriaminepentacetate, through reactions with its pendant primary amine groups. Using this approach, a significant increase in the labelling density of the VLP, compared to that of previous modifications of VLPs, can be achieved. These results highlight the use of multimeric protein-polymer conjugates for their potential utility in the development of VLP-based MRI contrast agents with the possibility of loading other cargos.

Effect of Spin-Orbit Coupling on the Actinide Dioxides AnO2 (An=Th, Pa, U, Np, Pu, and Am): A Screened Hybrid Density Functional Study

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

Wen, Xiaodong; Martin, Richard L.; Roy, Lindsay E.

2012-10-21

We present a systematic comparison of the lattice structures, electronic density of states, and band gaps of actinide dioxides, AnO₂ (An=Th, Pa, U, Np, Pu, and Am) predicted by the Heyd-Scuseria-Ernzerhof screened hybrid density functional (HSE) with the self-consistent inclusion of spin-orbit coupling(SOC). The computed HSE lattice constants and band gaps of AnO₂ are in consistently good agreement with the available experimental data across the series, and differ little from earlier HSE results without SOC. ThO₂ is a simple band insulator (f⁰), while PaO₂, UO₂, and NpO₂ are predicted to be Mott insulators. The remainders (PuO₂ and AmO₂) show considerablemore » O2p/An5f mixing and are classified as charge-transfer insulators. We also compare our results for UO₂, NpO₂, and PuO₂with the PBE+U, self interaction correction (SIC), and dynamic mean-field theory (DMFT) many-body approximations.« less

Course 4: Density Functional Theory, Methods, Techniques, and Applications

NASA Astrophysics Data System (ADS)

Chrétien, S.; Salahub, D. R.

Contents 1 Introduction 2 Density functional theory 2.1 Hohenberg and Kohn theorems 2.2 Levy's constrained search 2.3 Kohn-Sham method 3 Density matrices and pair correlation functions 4 Adiabatic connection or coupling strength integration 5 Comparing and constrasting KS-DFT and HF-CI 6 Preparing new functionals 7 Approximate exchange and correlation functionals 7.1 The Local Spin Density Approximation (LSDA) 7.2 Gradient Expansion Approximation (GEA) 7.3 Generalized Gradient Approximation (GGA) 7.4 meta-Generalized Gradient Approximation (meta-GGA) 7.5 Hybrid functionals 7.6 The Optimized Effective Potential method (OEP) 7.7 Comparison between various approximate functionals 8 LAP correlation functional 9 Solving the Kohn-Sham equations 9.1 The Kohn-Sham orbitals 9.2 Coulomb potential 9.3 Exchange-correlation potential 9.4 Core potential 9.5 Other choices and sources of error 9.6 Functionality 10 Applications 10.1 Ab initio molecular dynamics for an alanine dipeptide model 10.2 Transition metal clusters: The ecstasy, and the agony... 10.3 The conversion of acetylene to benzene on Fe clusters 11 Conclusions

Frequency and zero-point vibrational energy scale factors for double-hybrid density functionals (and other selected methods): can anharmonic force fields be avoided?

PubMed

Kesharwani, Manoj K; Brauer, Brina; Martin, Jan M L

2015-03-05

We have obtained uniform frequency scaling factors λ(harm) (for harmonic frequencies), λ(fund) (for fundamentals), and λ(ZPVE) (for zero-point vibrational energies (ZPVEs)) for the Weigend-Ahlrichs and other selected basis sets for MP2, SCS-MP2, and a variety of DFT functionals including double hybrids. For selected levels of theory, we have also obtained scaling factors for true anharmonic fundamentals and ZPVEs obtained from quartic force fields. For harmonic frequencies, the double hybrids B2PLYP, B2GP-PLYP, and DSD-PBEP86 clearly yield the best performance at RMSD = 10-12 cm(-1) for def2-TZVP and larger basis sets, compared to 5 cm(-1) at the CCSD(T) basis set limit. For ZPVEs, again, the double hybrids are the best performers, reaching root-mean-square deviations (RMSDs) as low as 0.05 kcal/mol, but even mainstream functionals like B3LYP can get down to 0.10 kcal/mol. Explicitly anharmonic ZPVEs only are marginally more accurate. For fundamentals, however, simple uniform scaling is clearly inadequate.

Curvature and frontier orbital energies in density functional theory

NASA Astrophysics Data System (ADS)

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

2013-03-01

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

Design, processing and testing of LSI arrays: Hybrid microelectronics task

NASA Technical Reports Server (NTRS)

Himmel, R. P.; Stuhlbarg, S. M.; Ravetti, R. G.; Zulueta, P. J.

1979-01-01

Mathematical cost factors were generated for both hybrid microcircuit and printed wiring board packaging methods. A mathematical cost model was created for analysis of microcircuit fabrication costs. The costing factors were refined and reduced to formulae for computerization. Efficient methods were investigated for low cost packaging of LSI devices as a function of density and reliability. Technical problem areas such as wafer bumping, inner/outer leading bonding, testing on tape, and tape processing, were investigated.

Improved treatment of exact exchange in Quantum ESPRESSO

DOE PAGES

Barnes, Taylor A.; Kurth, Thorsten; Carrier, Pierre; ...

2017-01-18

Here, we present an algorithm and implementation for the parallel computation of exact exchange in Quantum ESPRESSO (QE) that exhibits greatly improved strong scaling. QE is an open-source software package for electronic structure calculations using plane wave density functional theory, and supports the use of local, semi-local, and hybrid DFT functionals. Wider application of hybrid functionals is desirable for the improved simulation of electronic band energy alignments and thermodynamic properties, but the computational complexity of evaluating the exact exchange potential limits the practical application of hybrid functionals to large systems and requires efficient implementations. We demonstrate that existing implementations ofmore » hybrid DFT that utilize a single data structure for both the local and exact exchange regions of the code are significantly limited in the degree of parallelization achievable. We present a band-pair parallelization approach, in which the calculation of exact exchange is parallelized and evaluated independently from the parallelization of the remainder of the calculation, with the wavefunction data being efficiently transformed on-the-fly into a form that is optimal for each part of the calculation. For a 64 water molecule supercell, our new algorithm reduces the overall time to solution by nearly an order of magnitude.« less

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

Barnes, Taylor A.; Kurth, Thorsten; Carrier, Pierre

Here, we present an algorithm and implementation for the parallel computation of exact exchange in Quantum ESPRESSO (QE) that exhibits greatly improved strong scaling. QE is an open-source software package for electronic structure calculations using plane wave density functional theory, and supports the use of local, semi-local, and hybrid DFT functionals. Wider application of hybrid functionals is desirable for the improved simulation of electronic band energy alignments and thermodynamic properties, but the computational complexity of evaluating the exact exchange potential limits the practical application of hybrid functionals to large systems and requires efficient implementations. We demonstrate that existing implementations ofmore » hybrid DFT that utilize a single data structure for both the local and exact exchange regions of the code are significantly limited in the degree of parallelization achievable. We present a band-pair parallelization approach, in which the calculation of exact exchange is parallelized and evaluated independently from the parallelization of the remainder of the calculation, with the wavefunction data being efficiently transformed on-the-fly into a form that is optimal for each part of the calculation. For a 64 water molecule supercell, our new algorithm reduces the overall time to solution by nearly an order of magnitude.« less

3D hierarchical architecture based on 1D TiO2 nanorod and 2D MnO2 nanoflake for high performance supercapacitor electrode

NASA Astrophysics Data System (ADS)

Thakur, S.; Maiti, S.; Acharya, A.; Paul, T.; Besra, N.; Sarkar, S.; Chattopadhyay, K. K.

2018-04-01

Possibility of integration of manifold functionalities coupled with novel interface phenomenon generation in geometrically intricate hierarchical nanoform has made them greatly pertinent from both research and technological point of view. Here, oxide based hybrid has been realized by integrating 1D TiO2 nanorod with 2D MnO2 nanoflake via low temperature chemical route. Meticulous tunability over the hierarchical morphology was achieved by subtle variation of reaction parameter which in turn created difference in MnO2 growth over TiO2. Morphological features of the samples were examined by FESEM and TEM. Hybrid samples exhibited high electrochemical performance than pristine TiO2 nanorods. Registered electrochemical performance from TiO2-MnO2 hybrid was found to be ˜1024F/g at a current density of 0.66A/g which is ˜100 fold than TiO2 at same current density. Such enhanced performance is accounted from higher surface area and electrical conductivity of the hybrid.

Resolution of the Band Gap Prediction Problem for Materials Design

DOE PAGES

Crowley, Jason M.; Tahir-Kheli, Jamil; Goddard, William A.

2016-03-04

An important property with any new material is the band gap. Standard density functional theory methods grossly underestimate band gaps. This is known as the band gap problem. Here in this paper, we show that the hybrid B3PW91 density functional returns band gaps with a mean absolute deviation (MAD) from experiment of 0.22 eV over 64 insulators with gaps spanning a factor of 500 from 0.014 to 7 eV. The MAD is 0.28 eV over 70 compounds with gaps up to 14.2 eV, with a mean error of -0.03 eV. To benchmark the quality of the hybrid method, we comparedmore » the hybrid method to the rigorous GW many-body perturbation theory method. Surprisingly, the MAD for B3PW91 is about 1.5 times smaller than the MAD for GW. Furthermore, B3PW91 is 3-4 orders of magnitude faster computationally. Hence, B3PW91 is a practical tool for predicting band gaps of materials before they are synthesized and represents a solution to the band gap prediction problem.« less

Studying the varied shapes of gold clusters by an elegant optimization algorithm that hybridizes the density functional tight-binding theory and the density functional theory

NASA Astrophysics Data System (ADS)

Yen, Tsung-Wen; Lim, Thong-Leng; Yoon, Tiem-Leong; Lai, S. K.

2017-11-01

We combined a new parametrized density functional tight-binding (DFTB) theory (Fihey et al. 2015) with an unbiased modified basin hopping (MBH) optimization algorithm (Yen and Lai 2015) and applied it to calculate the lowest energy structures of Au clusters. From the calculated topologies and their conformational changes, we find that this DFTB/MBH method is a necessary procedure for a systematic study of the structural development of Au clusters but is somewhat insufficient for a quantitative study. As a result, we propose an extended hybridized algorithm. This improved algorithm proceeds in two steps. In the first step, the DFTB theory is employed to calculate the total energy of the cluster and this step (through running DFTB/MBH optimization for given Monte-Carlo steps) is meant to efficiently bring the Au cluster near to the region of the lowest energy minimum since the cluster as a whole has explicitly considered the interactions of valence electrons with ions, albeit semi-quantitatively. Then, in the second succeeding step, the energy-minimum searching process will continue with a skilledly replacement of the energy function calculated by the DFTB theory in the first step by one calculated in the full density functional theory (DFT). In these subsequent calculations, we couple the DFT energy also with the MBH strategy and proceed with the DFT/MBH optimization until the lowest energy value is found. We checked that this extended hybridized algorithm successfully predicts the twisted pyramidal structure for the Au40 cluster and correctly confirms also the linear shape of C8 which our previous DFTB/MBH method failed to do so. Perhaps more remarkable is the topological growth of Aun: it changes from a planar (n =3-11) → an oblate-like cage (n =12-15) → a hollow-shape cage (n =16-18) and finally a pyramidal-like cage (n =19, 20). These varied forms of the cluster's shapes are consistent with those reported in the literature.

Modeling and Density Estimation of an Urban Freeway Network Based on Dynamic Graph Hybrid Automata

PubMed Central

Chen, Yangzhou; Guo, Yuqi; Wang, Ying

2017-01-01

In this paper, in order to describe complex network systems, we firstly propose a general modeling framework by combining a dynamic graph with hybrid automata and thus name it Dynamic Graph Hybrid Automata (DGHA). Then we apply this framework to model traffic flow over an urban freeway network by embedding the Cell Transmission Model (CTM) into the DGHA. With a modeling procedure, we adopt a dual digraph of road network structure to describe the road topology, use linear hybrid automata to describe multi-modes of dynamic densities in road segments and transform the nonlinear expressions of the transmitted traffic flow between two road segments into piecewise linear functions in terms of multi-mode switchings. This modeling procedure is modularized and rule-based, and thus is easily-extensible with the help of a combination algorithm for the dynamics of traffic flow. It can describe the dynamics of traffic flow over an urban freeway network with arbitrary topology structures and sizes. Next we analyze mode types and number in the model of the whole freeway network, and deduce a Piecewise Affine Linear System (PWALS) model. Furthermore, based on the PWALS model, a multi-mode switched state observer is designed to estimate the traffic densities of the freeway network, where a set of observer gain matrices are computed by using the Lyapunov function approach. As an example, we utilize the PWALS model and the corresponding switched state observer to traffic flow over Beijing third ring road. In order to clearly interpret the principle of the proposed method and avoid computational complexity, we adopt a simplified version of Beijing third ring road. Practical application for a large-scale road network will be implemented by decentralized modeling approach and distributed observer designing in the future research. PMID:28353664

Modeling and Density Estimation of an Urban Freeway Network Based on Dynamic Graph Hybrid Automata.

PubMed

Chen, Yangzhou; Guo, Yuqi; Wang, Ying

2017-03-29

In this paper, in order to describe complex network systems, we firstly propose a general modeling framework by combining a dynamic graph with hybrid automata and thus name it Dynamic Graph Hybrid Automata (DGHA). Then we apply this framework to model traffic flow over an urban freeway network by embedding the Cell Transmission Model (CTM) into the DGHA. With a modeling procedure, we adopt a dual digraph of road network structure to describe the road topology, use linear hybrid automata to describe multi-modes of dynamic densities in road segments and transform the nonlinear expressions of the transmitted traffic flow between two road segments into piecewise linear functions in terms of multi-mode switchings. This modeling procedure is modularized and rule-based, and thus is easily-extensible with the help of a combination algorithm for the dynamics of traffic flow. It can describe the dynamics of traffic flow over an urban freeway network with arbitrary topology structures and sizes. Next we analyze mode types and number in the model of the whole freeway network, and deduce a Piecewise Affine Linear System (PWALS) model. Furthermore, based on the PWALS model, a multi-mode switched state observer is designed to estimate the traffic densities of the freeway network, where a set of observer gain matrices are computed by using the Lyapunov function approach. As an example, we utilize the PWALS model and the corresponding switched state observer to traffic flow over Beijing third ring road. In order to clearly interpret the principle of the proposed method and avoid computational complexity, we adopt a simplified version of Beijing third ring road. Practical application for a large-scale road network will be implemented by decentralized modeling approach and distributed observer designing in the future research.

Three-dimensional neutronics optimization of helium-cooled blanket for multi-functional experimental fusion-fission hybrid reactor (FDS-MFX)

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

Jiang, J.; Yuan, B.; Jin, M.

2012-07-01

Three-dimensional neutronics optimization calculations were performed to analyse the parameters of Tritium Breeding Ratio (TBR) and maximum average Power Density (PDmax) in a helium-cooled multi-functional experimental fusion-fission hybrid reactor named FDS (Fusion-Driven hybrid System)-MFX (Multi-Functional experimental) blanket. Three-stage tests will be carried out successively, in which the tritium breeding blanket, uranium-fueled blanket and spent-fuel-fueled blanket will be utilized respectively. In this contribution, the most significant and main goal of the FDS-MFX blanket is to achieve the PDmax of about 100 MW/m3 with self-sustaining tritium (TBR {>=} 1.05) based on the second-stage test with uranium-fueled blanket to check and validate themore » demonstrator reactor blanket relevant technologies based on the viable fusion and fission technologies. Four different enriched uranium materials were taken into account to evaluate PDmax in subcritical blanket: (i) natural uranium, (ii) 3.2% enriched uranium, (iii) 19.75% enriched uranium, and (iv) 64.4% enriched uranium carbide. These calculations and analyses were performed using a home-developed code VisualBUS and Hybrid Evaluated Nuclear Data Library (HENDL). The results showed that the performance of the blanket loaded with 64.4% enriched uranium was the most attractive and it could be promising to effectively obtain tritium self-sufficiency (TBR-1.05) and a high maximum average power density ({approx}100 MW/m{sup 3}) when the blanket was loaded with the mass of {sup 235}U about 1 ton. (authors)« less

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.

Spatial Electron-hole Separation in a One Dimensional Hybrid Organic-Inorganic Lead Iodide

NASA Astrophysics Data System (ADS)

Savory, Christopher N.; Palgrave, Robert G.; Bronstein, Hugo; Scanlon, David O.

2016-02-01

The increasing efficiency of the inorganic-organic hybrid halides has revolutionised photovoltaic research. Despite this rapid progress, the significant issues of poor stability and toxicity have yet to be suitably overcome. In this article, we use Density Functional Theory to examine (Pb2I6) · (H2DPNDI) · (H2O) · (NMP), an alternative lead-based hybrid inorganic-organic solar absorber based on a photoactive organic cation. Our results demonstrate that optical properties suitable for photovoltaic applications, in addition to spatial electron-hole separation, are possible but efficient charge transport may be a limiting factor.

Spatial Electron-hole Separation in a One Dimensional Hybrid Organic–Inorganic Lead Iodide

PubMed Central

Savory, Christopher N.; Palgrave, Robert G.; Bronstein, Hugo; Scanlon, David O.

2016-01-01

The increasing efficiency of the inorganic-organic hybrid halides has revolutionised photovoltaic research. Despite this rapid progress, the significant issues of poor stability and toxicity have yet to be suitably overcome. In this article, we use Density Functional Theory to examine (Pb2I6) · (H2DPNDI) · (H2O) · (NMP), an alternative lead-based hybrid inorganic-organic solar absorber based on a photoactive organic cation. Our results demonstrate that optical properties suitable for photovoltaic applications, in addition to spatial electron-hole separation, are possible but efficient charge transport may be a limiting factor. PMID:26858147

Projected Hybrid Orbitals: A General QM/MM Method

PubMed Central

2015-01-01

A projected hybrid orbital (PHO) method was described to model the covalent boundary in a hybrid quantum mechanical and molecular mechanical (QM/MM) system. The PHO approach can be used in ab initio wave function theory and in density functional theory with any basis set without introducing system-dependent parameters. In this method, a secondary basis set on the boundary atom is introduced to formulate a set of hybrid atomic orbtials. The primary basis set on the boundary atom used for the QM subsystem is projected onto the secondary basis to yield a representation that provides a good approximation to the electron-withdrawing power of the primary basis set to balance electronic interactions between QM and MM subsystems. The PHO method has been tested on a range of molecules and properties. Comparison with results obtained from QM calculations on the entire system shows that the present PHO method is a robust and balanced QM/MM scheme that preserves the structural and electronic properties of the QM region. PMID:25317748

A Screened Hybrid DFT Study of Actinide Oxides, Nitrides, and Carbides

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

Wen, Xiaodong; Martin, Richard L.; Scuseria, Gustavo E.

2013-06-27

A systematic study of the structural, electronic, and magnetic properties of actinide oxides, nitrides, and carbides (AnX1–2 with X = C, N, O) is performed using the Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Our computed results show that the screened hybrid HSE functional gives a good description of the electronic and structural properties of actinide dioxides (strongly correlated insulators) when compared with available experimental data. However, there are still some problems reproducing the electronic properties of actinide nitrides and carbides (strongly correlated metals). In addition, in order to compare with the results by HSE, the structures, electronic, and magnetic properties of thesemore » actinide compounds are also investigated in the PBE and PBE+U approximation. Interestingly, the density of states of UN obtained with PBE compares well with the experimental photoemission spectra, in contrast to the hybrid approximation. This is presumably related to the need of additional screening in the Hartree–Fock exchange term of the metallic phases.« less

Electromagnetic Properties Analysis on Hybrid-driven System of Electromagnetic Motor

NASA Astrophysics Data System (ADS)

Zhao, Jingbo; Han, Bingyuan; Bei, Shaoyi

2018-01-01

The hybrid-driven system made of permanent-and electromagnets applied in the electromagnetic motor was analyzed, equivalent magnetic circuit was used to establish the mathematical models of hybrid-driven system, based on the models of hybrid-driven system, the air gap flux, air-gap magnetic flux density, electromagnetic force was proposed. Taking the air-gap magnetic flux density and electromagnetic force as main research object, the hybrid-driven system was researched. Electromagnetic properties of hybrid-driven system with different working current modes is studied preliminary. The results shown that analysis based on hybrid-driven system can improve the air-gap magnetic flux density and electromagnetic force more effectively and can also guarantee the output stability, the effectiveness and feasibility of the hybrid-driven system are verified, which proved theoretical basis for the design of hybrid-driven system.

Optical properties of anthocyanins in the gas phase

NASA Astrophysics Data System (ADS)

Ge, Xiaochuan; Calzolari, Arrigo; Baroni, Stefano

2015-01-01

The gas-phase optical properties of the six most common anthocyanins are studied using time-dependent density-functional theory. Different anthocyanins are classified into three groups, according to the number of low-frequency peaks displayed in the UV-vis spectrum. This behavior is analyzed in terms of one-electron transitions and interaction effects, the latter being rationalized using a suitable double-pole model. Moving from PBE to hybrid exchange-correlation functionals results in a hypsochromic shift of the optical gap. While the colors thus predicted do not quite match those observed in solution, thus highlighting the importance of solvation effects, adoption of hybrid functionals remarkably determines a greater chromatic uniformity of different molecules, in qualitative agreement with experimental evidence in acidic solutions.

Nonlinear electronic excitations in crystalline solids using meta-generalized gradient approximation and hybrid functional in time-dependent density functional theory

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

Sato, Shunsuke A.; Taniguchi, Yasutaka; Department of Medical and General Sciences, Nihon Institute of Medical Science, 1276 Shimogawara, Moroyama-Machi, Iruma-Gun, Saitama 350-0435

2015-12-14

We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functionalmore » which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.« less

Explicit polarization (X-Pol) potential using ab initio molecular orbital theory and density functional theory.

PubMed

Song, Lingchun; Han, Jaebeom; Lin, Yen-lin; Xie, Wangshen; Gao, Jiali

2009-10-29

The explicit polarization (X-Pol) method has been examined using ab initio molecular orbital theory and density functional theory. The X-Pol potential was designed to provide a novel theoretical framework for developing next-generation force fields for biomolecular simulations. Importantly, the X-Pol potential is a general method, which can be employed with any level of electronic structure theory. The present study illustrates the implementation of the X-Pol method using ab initio Hartree-Fock theory and hybrid density functional theory. The computational results are illustrated by considering a set of bimolecular complexes of small organic molecules and ions with water. The computed interaction energies and hydrogen bond geometries are in good accord with CCSD(T) calculations and B3LYP/aug-cc-pVDZ optimizations.

Preparation and properties of CVD-graphene/AgNWs hybrid transparent electrodes for the application of flexible optoelectronic devices

NASA Astrophysics Data System (ADS)

Wang, Xue-yan; Bao, Jun; Li, Lu; Cui, Shao-li; Du, Xiao-qing

2017-10-01

The flexible electrodes based on CVD-graphene/ AgNWs hybrid transparent films were prepared by the vacuum filtration and substrate transferring method, and several performances of the films including sheet resistance, optical transmittance, work function, surface roughness and flexibility were further researched. The results suggested that the hybrid films which were obtained by vacuum filtration and substrate transferring method have the advantages such as uniform distribution of AgNWs, high work function, low roughness and small sheet resistance and good flexibility. The sheet resistance of the hybrid films would decrease with the increasing of the concentration of AgNWs, while the surface roughness would increase and the optical transmittance at 550nm of the films decrease linearly. Organic light emitting devices (OLED) devices based on CVD-graphene/AgNWs hybrid films were fabricated, and characteristics of voltage-current density, luminance, current efficiency were tested. It's found that CVD-graphene/AgNWs hybrid films were better than CVD-graphene films when they were used as anodes for organic light emitting devices. It can be seen that CVD-graphene/AgNWs hybrid transparent films have great potential in applications of flexible electrodes, and are of great significance for promoting the development of organic light emitting devices.

RFI in hybrid loops - Simulation and experimental results.

NASA Technical Reports Server (NTRS)

Ziemer, R. E.; Nelson, D. R.; Raghavan, H. R.

1972-01-01

A digital simulation of an imperfect second-order hybrid phase-locked loop (HPLL) operating in radio frequency interference (RFI) is described. Its performance is characterized in terms of phase error variance and phase error probability density function (PDF). Monte-Carlo simulation is used to show that the HPLL can be superior to the conventional phase-locked loops in RFI backgrounds when minimum phase error variance is the goodness criterion. Similar experimentally obtained data are given in support of the simulation data.

A Model for Lower Hybrid Wave Excitation Compared with Observations by Viking

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Liemohn, M. W.; Krivorutsky, E. N.; Horwitz, J. L.

1997-01-01

The mechanism of lower hybrid wave (LHW) excitation due to the O+ relative drift in a plasma subjected to low-frequency waves (LFWs) is used for analysis of Viking satellite data for events in the cusp/cleft region. In some cases, such a mechanism leads to LHW energy densities and ion distribution functions close to those observed, suggesting the proposed mechanism is a plausible candidate to explain certain classes of LHW generation events in space plasmas.

Physical Meaning of Virtual Kohn-Sham Orbitals and Orbital Energies: An Ideal Basis for the Description of Molecular Excitations.

PubMed

van Meer, R; Gritsenko, O V; Baerends, E J

2014-10-14

In recent years, several benchmark studies on the performance of large sets of functionals in time-dependent density functional theory (TDDFT) calculations of excitation energies have been performed. The tested functionals do not approximate exact Kohn-Sham orbitals and orbital energies closely. We highlight the advantages of (close to) exact Kohn-Sham orbitals and orbital energies for a simple description, very often as just a single orbital-to-orbital transition, of molecular excitations. Benchmark calculations are performed for the statistical average of orbital potentials (SAOP) functional for the potential [J. Chem. Phys. 2000, 112, 1344; 2001, 114, 652], which approximates the true Kohn-Sham potential much better than LDA, GGA, mGGA, and hybrid potentials do. An accurate Kohn-Sham potential does not only perform satisfactorily for calculated vertical excitation energies of both valence and Rydberg transitions but also exhibits appealing properties of the KS orbitals including occupied orbital energies close to ionization energies, virtual-occupied orbital energy gaps very close to excitation energies, realistic shapes of virtual orbitals, leading to straightforward interpretation of most excitations as single orbital transitions. We stress that such advantages are completely lost in time-dependent Hartree-Fock and partly in hybrid approaches. Many excitations and excitation energies calculated with local density, generalized gradient, and hybrid functionals are spurious. There is, with an accurate KS, or even the LDA or GGA potentials, nothing problematic about the "band gap" in molecules: the HOMO-LUMO gap is close to the first excitation energy (the optical gap).

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine.

PubMed

Wu, Wei

2014-06-14

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-½) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by the long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.

Increasing the applicability of density functional theory. IV. Consequences of ionization-potential improved exchange-correlation potentials.

PubMed

Verma, Prakash; Bartlett, Rodney J

2014-05-14

This paper's objective is to create a "consistent" mean-field based Kohn-Sham (KS) density functional theory (DFT) meaning the functional should not only provide good total energy properties, but also the corresponding KS eigenvalues should be accurate approximations to the vertical ionization potentials (VIPs) of the molecule, as the latter condition attests to the viability of the exchange-correlation potential (VXC). None of the prominently used DFT approaches show these properties: the optimized effective potential VXC based ab initio dft does. A local, range-separated hybrid potential cam-QTP-00 is introduced as the basis for a "consistent" KS DFT approach. The computed VIPs as the negative of KS eigenvalue have a mean absolute error of 0.8 eV for an extensive set of molecule's electron ionizations, including the core. Barrier heights, equilibrium geometries, and magnetic properties obtained from the potential are in good agreement with experiment. A similar accuracy with less computational efforts can be achieved by using a non-variational global hybrid variant of the QTP-00 approach.

Coupling density functional theory to polarizable force fields for efficient and accurate Hamiltonian molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Schwörer, Magnus; Breitenfeld, Benedikt; Tröster, Philipp; Bauer, Sebastian; Lorenzen, Konstantin; Tavan, Paul; Mathias, Gerald

2013-06-01

Hybrid molecular dynamics (MD) simulations, in which the forces acting on the atoms are calculated by grid-based density functional theory (DFT) for a solute molecule and by a polarizable molecular mechanics (PMM) force field for a large solvent environment composed of several 103-105 molecules, pose a challenge. A corresponding computational approach should guarantee energy conservation, exclude artificial distortions of the electron density at the interface between the DFT and PMM fragments, and should treat the long-range electrostatic interactions within the hybrid simulation system in a linearly scaling fashion. Here we describe a corresponding Hamiltonian DFT/(P)MM implementation, which accounts for inducible atomic dipoles of a PMM environment in a joint DFT/PMM self-consistency iteration. The long-range parts of the electrostatics are treated by hierarchically nested fast multipole expansions up to a maximum distance dictated by the minimum image convention of toroidal boundary conditions and, beyond that distance, by a reaction field approach such that the computation scales linearly with the number of PMM atoms. Short-range over-polarization artifacts are excluded by using Gaussian inducible dipoles throughout the system and Gaussian partial charges in the PMM region close to the DFT fragment. The Hamiltonian character, the stability, and efficiency of the implementation are investigated by hybrid DFT/PMM-MD simulations treating one molecule of the water dimer and of bulk water by DFT and the respective remainder by PMM.

Solar-microbial hybrid device based on oxygen-deficient niobium pentoxide anodes for sustainable hydrogen production.

PubMed

Li, Mingyang; He, Xinjun; Zeng, Yinxiang; Chen, Meiqiong; Zhang, Ziyang; Yang, Hao; Fang, Pingping; Lu, Xihong; Tong, Yexiang

2015-12-01

Hydrogen gas is emerging as an attractive fuel with high energy density for the direction of energy resources in the future. Designing integrated devices based on a photoelectrochemical (PEC) cell and a microbial fuel cell (MFC) represents a promising strategy to produce hydrogen fuel at a low price. In this work, we demonstrate a new solar-microbial (PEC-MFC) hybrid device based on the oxygen-deficient Nb 2 O 5 nanoporous (Nb 2 O 5- x NPs) anodes for sustainable hydrogen generation without external bias for the first time. Owing to the improved conductivity and porous structure, the as-prepared Nb 2 O 5- x NPs film yields a remarkable photocurrent density of 0.9 mA cm -2 at 0.6 V ( vs. SCE) in 1 M KOH aqueous solution under light irradiation, and can achieve a maximum power density of 1196 mW m -2 when used as an anode in a MFC device. More importantly, a solar-microbial hybrid system by combining a PEC cell with a MFC is designed, in which the Nb 2 O 5- x NPs electrodes function as both anodes. The as-fabricated PEC-MFC hybrid device can simultaneously realize electricity and hydrogen using organic matter and solar light at zero external bias. This novel design and attempt might provide guidance for other materials to convert and store energy.

Fragment-based 13C nuclear magnetic resonance chemical shift predictions in molecular crystals: An alternative to planewave methods

NASA Astrophysics Data System (ADS)

Hartman, Joshua D.; Monaco, Stephen; Schatschneider, Bohdan; Beran, Gregory J. O.

2015-09-01

We assess the quality of fragment-based ab initio isotropic 13C chemical shift predictions for a collection of 25 molecular crystals with eight different density functionals. We explore the relative performance of cluster, two-body fragment, combined cluster/fragment, and the planewave gauge-including projector augmented wave (GIPAW) models relative to experiment. When electrostatic embedding is employed to capture many-body polarization effects, the simple and computationally inexpensive two-body fragment model predicts both isotropic 13C chemical shifts and the chemical shielding tensors as well as both cluster models and the GIPAW approach. Unlike the GIPAW approach, hybrid density functionals can be used readily in a fragment model, and all four hybrid functionals tested here (PBE0, B3LYP, B3PW91, and B97-2) predict chemical shifts in noticeably better agreement with experiment than the four generalized gradient approximation (GGA) functionals considered (PBE, OPBE, BLYP, and BP86). A set of recommended linear regression parameters for mapping between calculated chemical shieldings and observed chemical shifts are provided based on these benchmark calculations. Statistical cross-validation procedures are used to demonstrate the robustness of these fits.

Fragment-based (13)C nuclear magnetic resonance chemical shift predictions in molecular crystals: An alternative to planewave methods.

PubMed

Hartman, Joshua D; Monaco, Stephen; Schatschneider, Bohdan; Beran, Gregory J O

2015-09-14

We assess the quality of fragment-based ab initio isotropic (13)C chemical shift predictions for a collection of 25 molecular crystals with eight different density functionals. We explore the relative performance of cluster, two-body fragment, combined cluster/fragment, and the planewave gauge-including projector augmented wave (GIPAW) models relative to experiment. When electrostatic embedding is employed to capture many-body polarization effects, the simple and computationally inexpensive two-body fragment model predicts both isotropic (13)C chemical shifts and the chemical shielding tensors as well as both cluster models and the GIPAW approach. Unlike the GIPAW approach, hybrid density functionals can be used readily in a fragment model, and all four hybrid functionals tested here (PBE0, B3LYP, B3PW91, and B97-2) predict chemical shifts in noticeably better agreement with experiment than the four generalized gradient approximation (GGA) functionals considered (PBE, OPBE, BLYP, and BP86). A set of recommended linear regression parameters for mapping between calculated chemical shieldings and observed chemical shifts are provided based on these benchmark calculations. Statistical cross-validation procedures are used to demonstrate the robustness of these fits.

An extended hybrid density functional (X3LYP) with improved descriptions of nonbond interactions and thermodynamic properties of molecular systems.

PubMed

Xu, Xin; Zhang, Qingsong; Muller, Richard P; Goddard, William A

2005-01-01

We derive here the form for the exact exchange energy density for a density that decays with Gaussian-type behavior at long range. This functional is intermediate between the B88 and the PW91 exchange functionals. Using this modified functional to match the form expected for Gaussian densities, we propose the X3LYP extended functional. We find that X3LYP significantly outperforms Becke three parameter Lee-Yang-Parr (B3LYP) for describing van der Waals and hydrogen bond interactions, while performing slightly better than B3LYP for predicting heats of formation, ionization potentials, electron affinities, proton affinities, and total atomic energies as validated with the extended G2 set of atoms and molecules. Thus X3LYP greatly enlarges the field of applications for density functional theory. In particular the success of X3LYP in describing the water dimer (with R(e) and D(e) within the error bars of the most accurate determinations) makes it an excellent candidate for predicting accurate ligand-protein and ligand-DNA interactions. (c) 2005 American Institute of Physics.

Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics.

PubMed

Hutchins, Daniel O; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E; Castner, David G; Ma, Hong; Jen, Alex K-Y

2012-11-15

Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlO x (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10 -8 A cm -2 and capacitance density of 0.62 µF cm -2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm 2 V -1 s -1 .

Solid-State Densification of Spun-Cast Self-Assembled Monolayers for Use in Ultra-Thin Hybrid Dielectrics

PubMed Central

Hutchins, Daniel O.; Acton, Orb; Weidner, Tobias; Cernetic, Nathan; Baio, Joe E.; Castner, David G.; Ma, Hong; Jen, Alex K.-Y.

2013-01-01

Ultra-thin self-assembled monolayer (SAM)-oxide hybrid dielectrics have gained significant interest for their application in low-voltage organic thin film transistors (OTFTs). A [8-(11-phenoxy-undecyloxy)-octyl]phosphonic acid (PhO-19-PA) SAM on ultrathin AlOx (2.5 nm) has been developed to significantly enhance the dielectric performance of inorganic oxides through reduction of leakage current while maintaining similar capacitance to the underlying oxide structure. Rapid processing of this SAM in ambient conditions is achieved by spin coating, however, as-cast monolayer density is not sufficient for dielectric applications. Thermal annealing of a bulk spun-cast PhO-19-PA molecular film is explored as a mechanism for SAM densification. SAM density, or surface coverage, and order are examined as a function of annealing temperature. These SAM characteristics are probed through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). It is found that at temperatures sufficient to melt the as-cast bulk molecular film, SAM densification is achieved; leading to a rapid processing technique for high performance SAM-oxide hybrid dielectric systems utilizing a single wet processing step. To demonstrate low-voltage devices based on this hybrid dielectric (with leakage current density of 7.7×10−8 A cm−2 and capacitance density of 0.62 µF cm−2 at 3 V), pentacene thin-film transistors (OTFTs) are fabricated and yield sub 2 V operation and charge carrier mobilites of up to 1.1 cm2 V−1 s−1. PMID:24288423

Charge localization and ordering in A 2 Mn 8 O 16 hollandite group oxides: Impact of density functional theory approaches

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

Kaltak, Merzuk; Fernandez-Serra, Marivi; Hybertsen, Mark S.

The phases of A 2Mn 8O 16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3d electrons are more explicitly considered with the DFT + Umore » approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn 3+ centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Lastly, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.« less

Charge localization and ordering in A 2 Mn 8 O 16 hollandite group oxides: Impact of density functional theory approaches

DOE PAGES

Kaltak, Merzuk; Fernandez-Serra, Marivi; Hybertsen, Mark S.

2017-12-01

The phases of A 2Mn 8O 16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3d electrons are more explicitly considered with the DFT + Umore » approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn 3+ centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Lastly, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.« less

Charge localization and ordering in A2Mn8O16 hollandite group oxides: Impact of density functional theory approaches

NASA Astrophysics Data System (ADS)

Kaltak, Merzuk; Fernández-Serra, Marivi; Hybertsen, Mark S.

2017-12-01

The phases of A2Mn8O16 hollandite group oxides emerge from the competition between ionic interactions, Jahn-Teller effects, charge ordering, and magnetic interactions. Their balanced treatment with feasible computational approaches can be challenging for commonly used approximations in density functional theory. Three examples (A = Ag, Li, and K) are studied with a sequence of different approximate exchange-correlation functionals. Starting from a generalized gradient approximation (GGA), an extension to include van der Waals interactions and a recently proposed meta-GGA are considered. Then local Coulomb interactions for the Mn 3 d electrons are more explicitly considered with the DFT + U approach. Finally, selected results from a hybrid functional approach provide a reference. Results for the binding energy of the A species in the parent oxide highlight the role of van der Waals interactions. Relatively accurate results for insertion energies can be achieved with a low-U and a high-U approach. In the low-U case, the materials are described as band metals with a high-symmetry, tetragonal crystal structure. In the high-U case, the electrons donated by A result in formation of local Mn3 + centers and corresponding Jahn-Teller distortions characterized by a local order parameter. The resulting degree of monoclinic distortion depends on charge ordering and magnetic interactions in the phase formed. The reference hybrid functional results show charge localization and ordering. Comparison to low-temperature experiments of related compounds suggests that charge localization is the physically correct result for the hollandite group oxides studied here. Finally, while competing effects in the local magnetic coupling are subtle, the fully anisotropic implementation of DFT + U gives the best overall agreement with results from the hybrid functional.

Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional

DOE PAGES

Liu, Zhen-Fei; Egger, David A.; Refaely-Abramson, Sivan; ...

2017-02-21

The alignment of the frontier orbital energies of an adsorbed molecule with the substrate Fermi level at metal-organic interfaces is a fundamental observable of significant practical importance in nanoscience and beyond. Typical density functional theory calculations, especially those using local and semi-local functionals, often underestimate level alignment leading to inaccurate electronic structure and charge transport properties. Here, we develop a new fully self-consistent predictive scheme to accurately compute level alignment at certain classes of complex heterogeneous molecule-metal interfaces based on optimally tuned range-separated hybrid functionals. Starting from a highly accurate description of the gas-phase electronic structure, our method by constructionmore » captures important nonlocal surface polarization effects via tuning of the long-range screened exchange in a range-separated hybrid in a non-empirical and system-specific manner. We implement this functional in a plane-wave code and apply it to several physisorbed and chemisorbed molecule-metal interface systems. Our results are in quantitative agreement with experiments, the both the level alignment and work function changes. This approach constitutes a new practical scheme for accurate and efficient calculations of the electronic structure of molecule-metal interfaces.« less

Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional

NASA Astrophysics Data System (ADS)

Liu, Zhen-Fei; Egger, David A.; Refaely-Abramson, Sivan; Kronik, Leeor; Neaton, Jeffrey B.

2017-03-01

The alignment of the frontier orbital energies of an adsorbed molecule with the substrate Fermi level at metal-organic interfaces is a fundamental observable of significant practical importance in nanoscience and beyond. Typical density functional theory calculations, especially those using local and semi-local functionals, often underestimate level alignment leading to inaccurate electronic structure and charge transport properties. In this work, we develop a new fully self-consistent predictive scheme to accurately compute level alignment at certain classes of complex heterogeneous molecule-metal interfaces based on optimally tuned range-separated hybrid functionals. Starting from a highly accurate description of the gas-phase electronic structure, our method by construction captures important nonlocal surface polarization effects via tuning of the long-range screened exchange in a range-separated hybrid in a non-empirical and system-specific manner. We implement this functional in a plane-wave code and apply it to several physisorbed and chemisorbed molecule-metal interface systems. Our results are in quantitative agreement with experiments, the both the level alignment and work function changes. Our approach constitutes a new practical scheme for accurate and efficient calculations of the electronic structure of molecule-metal interfaces.

Electronic, structural, and thermodynamic properties of mixed actinide dioxides (U, Pu, Am) O2 from hybrid density functional theory

NASA Astrophysics Data System (ADS)

Ma, Li; Ray, Asok K.

2010-03-01

As a continuation of our studies of pure actinide metals using hybrid density functional theory,footnotetextR. Atta-Fynn and A. K. Ray, Europhysics Letters, 85, 27008-p1- p6 (2009); Chemical Physics Letters, 482, 223-227 (2009). we present here a systematic study of the electronic and geometric structure properties of mixed actinide dioxides, U0.5Pu0.5O2, U0.5Am0.5O2, Pu0.5Am0.5 O2 and U0.8Pu0.2O2. The fraction of exact Hartree-Fock exchange used was 40%. To investigate the effect of spin-orbit coupling on the ground state electronic and geometric structure properties, computations have been carried out at two theoretical levels, one at the scalar-relativistic level with no spin-orbit coupling and one at the fully relativistic level with spin-orbit coupling. Thermodynamic properties have been calculated by a coupling of first-principles calculation and lattice dynamics.

A hybrid CS-SA intelligent approach to solve uncertain dynamic facility layout problems considering dependency of demands

NASA Astrophysics Data System (ADS)

Moslemipour, Ghorbanali

2018-07-01

This paper aims at proposing a quadratic assignment-based mathematical model to deal with the stochastic dynamic facility layout problem. In this problem, product demands are assumed to be dependent normally distributed random variables with known probability density function and covariance that change from period to period at random. To solve the proposed model, a novel hybrid intelligent algorithm is proposed by combining the simulated annealing and clonal selection algorithms. The proposed model and the hybrid algorithm are verified and validated using design of experiment and benchmark methods. The results show that the hybrid algorithm has an outstanding performance from both solution quality and computational time points of view. Besides, the proposed model can be used in both of the stochastic and deterministic situations.

When 2D Materials Meet Molecules: Opportunities and Challenges of Hybrid Organic/Inorganic van der Waals Heterostructures.

PubMed

Gobbi, Marco; Orgiu, Emanuele; Samorì, Paolo

2018-05-01

van der Waals heterostructures, composed of vertically stacked inorganic 2D materials, represent an ideal platform to demonstrate novel device architectures and to fabricate on-demand materials. The incorporation of organic molecules within these systems holds an immense potential, since, while nature offers a finite number of 2D materials, an almost unlimited variety of molecules can be designed and synthesized with predictable functionalities. The possibilities offered by systems in which continuous molecular layers are interfaced with inorganic 2D materials to form hybrid organic/inorganic van der Waals heterostructures are emphasized. Similar to their inorganic counterpart, the hybrid structures have been exploited to put forward novel device architectures, such as antiambipolar transistors and barristors. Moreover, specific molecular groups can be employed to modify intrinsic properties and confer new capabilities to 2D materials. In particular, it is highlighted how molecular self-assembly at the surface of 2D materials can be mastered to achieve precise control over position and density of (molecular) functional groups, paving the way for a new class of hybrid functional materials whose final properties can be selected by careful molecular design. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A comparative density functional study on electrical properties of layered penta-graphene

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

Yu, Zhi Gen, E-mail: yuzg@ihpc.a-star.edu.sg; Zhang, Yong-Wei, E-mail: zhangyw@ihpc.a-star.edu.sg

We present a comparative study of the influence of the number of layers, the biaxial strain in the range of −3% to 3%, and the stacking misalignments on the electronic properties of a new 2D carbon allotrope, penta-graphene (PG), based on hybrid-functional method within the density functional theory (DFT). In comparison with local exchange-correlation approximation in the DFT, the hybrid-functional provides an accurate description on the degree of p{sub z} orbitals localization and bandgap. Importantly, the predicted bandgap of few-layer PG has a weak layer dependence. The bandgap of monolayer PG is 3.27 eV, approximately equal to those of GaN andmore » ZnO; and the bandgap of few-layer PG decreases slowly with the number of layers (N) and converge to 2.57 eV when N ≥ 4. Our calculations using HSE06 functional on few-layer PG reveal that bandgap engineering by stacking misalignment can further tune the bandgap down to 1.37 eV. Importantly, there is no direct-to-indirect bandgap transition in PG by varying strain, layer number, and stacking misalignment. Owing to its tunable, robustly direct, and wide bandgap characteristics, few-layer PG is promising for optoelectronic and photovoltaic applications.« less

Scanning tunneling microscopy image simulation of the rutile (110) TiO2 surface with hybrid functionals and the localized basis set approach

NASA Astrophysics Data System (ADS)

Di Valentin, Cristiana

2007-10-01

In this work we present a simplified procedure to use hybrid functionals and localized atomic basis sets to simulate scanning tunneling microscopy (STM) images of stoichiometric, reduced and hydroxylated rutile (110) TiO2 surface. For the two defective systems it is necessary to introduce some exact Hartree-Fock exchange in the exchange functional in order to correctly describe the details of the electronic structure. Results are compared to the standard density functional theory and planewave basis set approach. Both methods have advantages and drawbacks that are analyzed in detail. In particular, for the localized basis set approach, it is necessary to introduce a number of Gaussian function in the vacuum region above the surface in order to correctly describe the exponential decay of the integrated local density of states from the surface. In the planewave periodic approach, a thick vacuum region is required to achieve correct results. Simulated STM images are obtained for both the reduced and hydroxylated surface which nicely compare with experimental findings. A direct comparison of the two defects as displayed in the simulated STM images indicates that the OH groups should appear brighter than oxygen vacancies in perfect agreement with the experimental STM data.

Influence of xc functional on thermal-elastic properties of Ceria: A DFT-based Debye-Grüneisen model approach

NASA Astrophysics Data System (ADS)

Lee, Ji-Hwan; Tak, Youngjoo; Lee, Taehun; Soon, Aloysius

Ceria (CeO2-x) is widely studied as a choice electrolyte material for intermediate-temperature (~ 800 K) solid oxide fuel cells. At this temperature, maintaining its chemical stability and thermal-mechanical integrity of this oxide are of utmost importance. To understand their thermal-elastic properties, we firstly test the influence of various approximations to the density-functional theory (DFT) xc functionals on specific thermal-elastic properties of both CeO2 and Ce2O3. Namely, we consider the local-density approximation (LDA), the generalized gradient approximation (GGA-PBE) with and without additional Hubbard U as applied to the 4 f electron of Ce, as well as the recently popularized hybrid functional due to Heyd-Scuseria-Ernzehof (HSE06). Next, we then couple this to a volume-dependent Debye-Grüneisen model to determine the thermodynamic quantities of ceria at arbitrary temperatures. We find an explicit description of the strong correlation (e.g. via the DFT + U and hybrid functional approach) is necessary to have a good agreement with experimental values, in contrast to the mean-field treatment in standard xc approximations (such as LDA or GGA-PBE). We acknowledge support from Samsung Research Funding Center of Samsung Electronics (SRFC-MA1501-03).

Assessing the role of Hartree-Fock exchange, correlation energy and long range corrections in evaluating ionization potential, and electron affinity in density functional theory.

PubMed

Vikramaditya, Talapunur; Lin, Shiang-Tai

2017-06-05

Accurate determination of ionization potentials (IPs), electron affinities (EAs), fundamental gaps (FGs), and HOMO, LUMO energy levels of organic molecules play an important role in modeling and predicting the efficiencies of organic photovoltaics, OLEDs etc. In this work, we investigate the effects of Hartree Fock (HF) Exchange, correlation energy, and long range corrections in predicting IP and EA in Hybrid Functionals. We observe increase in percentage of HF exchange results in increase of IPs and decrease in EAs. Contrary to the general expectations inclusion of both HF exchange and correlation energy (from the second order perturbation theory MP2) leads to poor prediction. Range separated Hybrid Functionals are found to be more reliable among various DFT Functionals investigated. DFT Functionals predict accurate IPs whereas post HF methods predict accurate EAs. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

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

PubMed

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

2012-03-08

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

Theoretical calculations of Electron Paramagnetic Resonance parameters of liquid phase Orotic acid radical

NASA Astrophysics Data System (ADS)

Sarikaya, Ebru Karakaş; Dereli, Ömer

2017-02-01

To obtain liquid phase molecular structure, conformational analysis of Orotic acid was performed and six conformers were determined. For these conformations, eight possible radicals were modelled by using Density Functional Theory computations with respect to molecular structure. Electron Paramagnetic Resonance parameters of these model radicals were calculated and then they were compared with the experimental ones. Geometry optimizations of the molecule and modeled radicals were performed using Becke's three-parameter hybrid-exchange functional combined with the Lee-Yang-Parr correlation functional of Density Functional Theory and 6-311++G(d,p) basis sets in p-dioxane solution. Because Orotic acid can be mutagenic in mammalian somatic cells and it is also mutagenic for bacteria and yeast, it has been studied.

Structural and Morphological Investigation for Water-Processed Graphene Oxide/Single-Walled Carbon Nanotubes Hybrids

NASA Astrophysics Data System (ADS)

Muda, M. R.; Ramli, M. M.; Mat Isa, S. S.; Halin, D. S. C.; Talip, L. F. A.; Mazelan, N. S.; Anhar, N. A. M.; Danial, N. A.

2017-06-01

New group of materials derived from hybridization of single walled carbon nanotubes (SWCNTs) and graphene oxide (GO) which resulting novel three dimensional (3D) materials generates an outstanding properties compared to corresponding SWCNTs and GO/Graphene. In this paper, we describe a simple approach using water processing method to develop integrated rGO/GO-SWCNT hybrids with different hybrid ratios. The hybrid ratios were varied into three divided ratio and the results were compared between pristine SWCNTs and GO in order to investigate the structural density and morphology of these carbonaceous materials. With an optimized ratio of rGO/GO-SWCNT, the hybrid shows a well-organized hybrid film structures with less defects density sites. The optimized mixture ratio emphasized the important of both rGO and SWCNTs in the hybrid structures. Morphological structural and defects density degrees were examined by Field Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy.

A study of accurate exchange-correlation functionals through adiabatic connection

NASA Astrophysics Data System (ADS)

Singh, Rabeet; Harbola, Manoj K.

2017-10-01

A systematic way of improving exchange-correlation energy functionals of density functional theory has been to make them satisfy more and more exact relations. Starting from the initial generalized gradient approximation (GGA) functionals, this has culminated into the recently proposed SCAN (strongly constrained and appropriately normed) functional that satisfies several known constraints and is appropriately normed. The ultimate test for the functionals developed is the accuracy of energy calculated by employing them. In this paper, we test these exchange-correlation functionals—the GGA hybrid functionals B3LYP and PBE0 and the meta-GGA functional SCAN—from a different perspective. We study how accurately these functionals reproduce the exchange-correlation energy when electron-electron interaction is scaled as αVee with α varying between 0 and 1. Our study reveals interesting comparison between these functionals and the associated difference Tc between the interacting and the non-interacting kinetic energy for the same density.

Microstructure and Dynamic Failure Properties of Freeze-Cast Materials for Thermobaric Warhead Cases

DTIC Science & Technology

2012-12-01

Function LLNL Lawrence Livermore National Laboratory PDF Probability Density Function PMMA Poly(Methyl Methacrylate) RM Reactive Materials SEM...FREEZE CAST MATERIALS Freeze casting technology combines compounds such as aluminum oxide and poly(methyl methacrylate) ( PMMA ) to develop a...Subsequently, the porous structure can be infiltrated with a variety of materials, such as a standard polymer like PMMA . This hybrid material is believed

Periodic density functional theory study of spin crossover in the cesium iron hexacyanochromate prussian blue analog

NASA Astrophysics Data System (ADS)

Wojdeł, Jacek C.; Moreira, Ibério de P. R.; Illas, Francesc

2009-01-01

This paper presents a detailed theoretical analysis of the electronic structure of the CsFe[Cr(CN)6] prussian blue analog with emphasis on the structural origin of the experimentally observed spin crossover transition in this material. Periodic density functional calculations using generalized gradient approximation (GGA)+U and nonlocal hybrid exchange-correlation potentials show that, for the experimental low temperature crystal structure, the t2g6eg0 low spin configuration of FeII is the most stable and CrIII (S =3/2, t2g3eg0) remains the same in all cases. This is also found to be the case for the low spin GGA+U fully relaxed structure with the optimized unit cell. A completely different situation emerges when calculations are carried out using the experimental high temperature structure. Here, GGA+U and hybrid density functional theory calculations consistently predict that the t2g4eg2 FeII high spin configuration is the ground state. However, the two spin configurations appear to be nearly degenerate when calculations are carried out for the geometries arising from a GGA+U full relaxation of the atomic structure carried out at experimental high temperature lattice constant. A detailed analysis of the energy difference between the two spin configurations as a function of the lattice constant strongly suggests that the observed spin crossover transition has a structural origin with non-negligible entropic contributions of the high spin state.

Current Density Functional Theory Using Meta-Generalized Gradient Exchange-Correlation Functionals.

PubMed

Furness, James W; Verbeke, Joachim; Tellgren, Erik I; Stopkowicz, Stella; Ekström, Ulf; Helgaker, Trygve; Teale, Andrew M

2015-09-08

We present the self-consistent implementation of current-dependent (hybrid) meta-generalized gradient approximation (mGGA) density functionals using London atomic orbitals. A previously proposed generalized kinetic energy density is utilized to implement mGGAs in the framework of Kohn-Sham current density functional theory (KS-CDFT). A unique feature of the nonperturbative implementation of these functionals is the ability to seamlessly explore a wide range of magnetic fields up to 1 au (∼235 kT) in strength. CDFT functionals based on the TPSS and B98 forms are investigated, and their performance is assessed by comparison with accurate coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) data. In the weak field regime, magnetic properties such as magnetizabilities and nuclear magnetic resonance shielding constants show modest but systematic improvements over generalized gradient approximations (GGA). However, in the strong field regime, the mGGA-based forms lead to a significantly improved description of the recently proposed perpendicular paramagnetic bonding mechanism, comparing well with CCSD(T) data. In contrast to functionals based on the vorticity, these forms are found to be numerically stable, and their accuracy at high field suggests that the extension of mGGAs to CDFT via the generalized kinetic energy density should provide a useful starting point for further development of CDFT approximations.

Use of the rVV10 Nonlocal Correlation Functional in the B97M-V Density Functional: Defining B97M-rV and Related Functionals [On the Use of the rVV10 Nonlocal Correlation Functional in the B97M-V Density Functional: Defining B97M-rV and Related Functionals

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

Mardirossian, Narbe; Ruiz Pestana, Luis; Womack, James C.

The VV10 and rVV10 nonlocal correlation functionals are consistently implemented and assessed, with the goal of determining if the rVV10 nonlocal correlation functional can replace the VV10 nonlocal correlation functional in the recently developed B97M-V density functional, to give the B97M-rV density functional. Along the way, four density functionals are simultaneously tested: VV10, rVV10, B97M-V, and B97M-rV. An initial assessment is carried out across the S22 data set, and the short-range damping variable, b, is varied for all four density functionals in order to determine the sensitivity of the functionals to the empirical parameter. The results of this test indicatemore » that a value of b = 6 (fortuitously the same as that in B97M-V) is suitable for B97M-rV. The functionals are then compared across an extensive database of interaction energies, and it is demonstrated that B97M-rV either matches or outperforms B97M-V for all of the tests considered. Finally, the optimization of b across the S22 data set is extended to two range-separated hybrid density functionals, ωB97X-V and ωB97M-V, and a value of b = 6.2 is recommended for both ωB97X-rV and ωB97M-rV.« less

Use of the rVV10 Nonlocal Correlation Functional in the B97M-V Density Functional: Defining B97M-rV and Related Functionals [On the Use of the rVV10 Nonlocal Correlation Functional in the B97M-V Density Functional: Defining B97M-rV and Related Functionals

DOE PAGES

Mardirossian, Narbe; Ruiz Pestana, Luis; Womack, James C.; ...

2016-12-06

The VV10 and rVV10 nonlocal correlation functionals are consistently implemented and assessed, with the goal of determining if the rVV10 nonlocal correlation functional can replace the VV10 nonlocal correlation functional in the recently developed B97M-V density functional, to give the B97M-rV density functional. Along the way, four density functionals are simultaneously tested: VV10, rVV10, B97M-V, and B97M-rV. An initial assessment is carried out across the S22 data set, and the short-range damping variable, b, is varied for all four density functionals in order to determine the sensitivity of the functionals to the empirical parameter. The results of this test indicatemore » that a value of b = 6 (fortuitously the same as that in B97M-V) is suitable for B97M-rV. The functionals are then compared across an extensive database of interaction energies, and it is demonstrated that B97M-rV either matches or outperforms B97M-V for all of the tests considered. Finally, the optimization of b across the S22 data set is extended to two range-separated hybrid density functionals, ωB97X-V and ωB97M-V, and a value of b = 6.2 is recommended for both ωB97X-rV and ωB97M-rV.« less

Hierarchical assembly of viral nanotemplates with encoded microparticles via nucleic acid hybridization.

PubMed

Tan, Wui Siew; Lewis, Christina L; Horelik, Nicholas E; Pregibon, Daniel C; Doyle, Patrick S; Yi, Hyunmin

2008-11-04

We demonstrate hierarchical assembly of tobacco mosaic virus (TMV)-based nanotemplates with hydrogel-based encoded microparticles via nucleic acid hybridization. TMV nanotemplates possess a highly defined structure and a genetically engineered high density thiol functionality. The encoded microparticles are produced in a high throughput microfluidic device via stop-flow lithography (SFL) and consist of spatially discrete regions containing encoded identity information, an internal control, and capture DNAs. For the hybridization-based assembly, partially disassembled TMVs were programmed with linker DNAs that contain sequences complementary to both the virus 5' end and a selected capture DNA. Fluorescence microscopy, atomic force microscopy (AFM), and confocal microscopy results clearly indicate facile assembly of TMV nanotemplates onto microparticles with high spatial and sequence selectivity. We anticipate that our hybridization-based assembly strategy could be employed to create multifunctional viral-synthetic hybrid materials in a rapid and high-throughput manner. Additionally, we believe that these viral-synthetic hybrid microparticles may find broad applications in high capacity, multiplexed target sensing.

Efficient light emission from inorganic and organic semiconductor hybrid structures by energy-level tuning

PubMed Central

Schlesinger, R.; Bianchi, F.; Blumstengel, S.; Christodoulou, C.; Ovsyannikov, R.; Kobin, B.; Moudgil, K.; Barlow, S.; Hecht, S.; Marder, S.R.; Henneberger, F.; Koch, N.

2015-01-01

The fundamental limits of inorganic semiconductors for light emitting applications, such as holographic displays, biomedical imaging and ultrafast data processing and communication, might be overcome by hybridization with their organic counterparts, which feature enhanced frequency response and colour range. Innovative hybrid inorganic/organic structures exploit efficient electrical injection and high excitation density of inorganic semiconductors and subsequent energy transfer to the organic semiconductor, provided that the radiative emission yield is high. An inherent obstacle to that end is the unfavourable energy level offset at hybrid inorganic/organic structures, which rather facilitates charge transfer that quenches light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels, here comprising ZnO and a tailored ladder-type oligophenylene. The ZnO work function is substantially lowered with an organometallic donor monolayer, aligning the frontier levels of the inorganic and organic semiconductors. This increases the hybrid structure's radiative emission yield sevenfold, validating the relevance of our approach. PMID:25872919

Efficient light emission from inorganic and organic semiconductor hybrid structures by energy-level tuning.

PubMed

Schlesinger, R; Bianchi, F; Blumstengel, S; Christodoulou, C; Ovsyannikov, R; Kobin, B; Moudgil, K; Barlow, S; Hecht, S; Marder, S R; Henneberger, F; Koch, N

2015-04-15

The fundamental limits of inorganic semiconductors for light emitting applications, such as holographic displays, biomedical imaging and ultrafast data processing and communication, might be overcome by hybridization with their organic counterparts, which feature enhanced frequency response and colour range. Innovative hybrid inorganic/organic structures exploit efficient electrical injection and high excitation density of inorganic semiconductors and subsequent energy transfer to the organic semiconductor, provided that the radiative emission yield is high. An inherent obstacle to that end is the unfavourable energy level offset at hybrid inorganic/organic structures, which rather facilitates charge transfer that quenches light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels, here comprising ZnO and a tailored ladder-type oligophenylene. The ZnO work function is substantially lowered with an organometallic donor monolayer, aligning the frontier levels of the inorganic and organic semiconductors. This increases the hybrid structure's radiative emission yield sevenfold, validating the relevance of our approach.

Comparing Charge Transport in Oligonucleotides: RNA:DNA Hybrids and DNA Duplexes.

PubMed

Li, Yuanhui; Artés, Juan M; Qi, Jianqing; Morelan, Ian A; Feldstein, Paul; Anantram, M P; Hihath, Joshua

2016-05-19

Understanding the electronic properties of oligonucleotide systems is important for applications in nanotechnology, biology, and sensing systems. Here the charge-transport properties of guanine-rich RNA:DNA hybrids are compared to double-stranded DNA (dsDNA) duplexes with identical sequences. The conductance of the RNA:DNA hybrids is ∼10 times higher than the equivalent dsDNA, and conformational differences are determined to be the primary reason for this difference. The conductance of the RNA:DNA hybrids is also found to decrease more rapidly than dsDNA when the length is increased. Ab initio electronic structure and Green's function-based density of states calculations demonstrate that these differences arise because the energy levels are more spatially distributed in the RNA:DNA hybrid but that the number of accessible hopping sites is smaller. These combination results indicate that a simple hopping model that treats each individual guanine as a hopping site is insufficient to explain both a higher conductance and β value for RNA:DNA hybrids, and larger delocalization lengths must be considered.

The RPA Atomization Energy Puzzle.

PubMed

Ruzsinszky, Adrienn; Perdew, John P; Csonka, Gábor I

2010-01-12

There is current interest in the random phase approximation (RPA), a "fifth-rung" density functional for the exchange-correlation energy. RPA has full exact exchange and constructs the correlation with the help of the unoccupied Kohn-Sham orbitals. In many cases (uniform electron gas, jellium surface, and free atom), the correction to RPA is a short-ranged effect that is captured by a local spin density approximation (LSDA) or a generalized gradient approximation (GGA). Nonempirical density functionals for the correction to RPA were constructed earlier at the LSDA and GGA levels (RPA+), but they are constructed here at the fully nonlocal level (RPA++), using the van der Waals density functional (vdW-DF) of Langreth, Lundqvist, and collaborators. While they make important and helpful corrections to RPA total and ionization energies of free atoms, they correct the RPA atomization energies of molecules by only about 1 kcal/mol. Thus, it is puzzling that RPA atomization energies are, on average, about 10 kcal/mol lower than those of accurate values from experiment. We find here that a hybrid of 50% Perdew-Burke-Ernzerhof GGA with 50% RPA+ yields atomization energies much more accurate than either one does alone. This suggests a solution to the puzzle: While the proper correction to RPA is short-ranged in some systems, its contribution to the correlation hole can spread out in a molecule with multiple atomic centers, canceling part of the spread of the exact exchange hole (more so than in RPA or RPA+), making the true exchange-correlation hole more localized than in RPA or RPA+. This effect is not captured even by the vdW-DF nonlocality, but it requires the different kind of full nonlocality present in a hybrid functional.

On the accuracy of density-functional theory exchange-correlation functionals for H bonds in small water clusters: Benchmarks approaching the complete basis set limit

NASA Astrophysics Data System (ADS)

Santra, Biswajit; Michaelides, Angelos; Scheffler, Matthias

2007-11-01

The ability of several density-functional theory (DFT) exchange-correlation functionals to describe hydrogen bonds in small water clusters (dimer to pentamer) in their global minimum energy structures is evaluated with reference to second order Møller-Plesset perturbation theory (MP2). Errors from basis set incompleteness have been minimized in both the MP2 reference data and the DFT calculations, thus enabling a consistent systematic evaluation of the true performance of the tested functionals. Among all the functionals considered, the hybrid X3LYP and PBE0 functionals offer the best performance and among the nonhybrid generalized gradient approximation functionals, mPWLYP and PBE1W perform best. The popular BLYP and B3LYP functionals consistently underbind and PBE and PW91 display rather variable performance with cluster size.

On the accuracy of density-functional theory exchange-correlation functionals for H bonds in small water clusters: benchmarks approaching the complete basis set limit.

PubMed

Santra, Biswajit; Michaelides, Angelos; Scheffler, Matthias

2007-11-14

The ability of several density-functional theory (DFT) exchange-correlation functionals to describe hydrogen bonds in small water clusters (dimer to pentamer) in their global minimum energy structures is evaluated with reference to second order Moller-Plesset perturbation theory (MP2). Errors from basis set incompleteness have been minimized in both the MP2 reference data and the DFT calculations, thus enabling a consistent systematic evaluation of the true performance of the tested functionals. Among all the functionals considered, the hybrid X3LYP and PBE0 functionals offer the best performance and among the nonhybrid generalized gradient approximation functionals, mPWLYP and PBE1W perform best. The popular BLYP and B3LYP functionals consistently underbind and PBE and PW91 display rather variable performance with cluster size.

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.

Electron momentum density and band structure calculations of α- and β-GeTe

NASA Astrophysics Data System (ADS)

Vadkhiya, Laxman; Arora, Gunjan; Rathor, Ashish; Ahuja, B. L.

2011-12-01

We have measured isotropic experimental Compton profile of α-GeTe by employing high energy (662 keV) γ-radiation from a 137Cs isotope. To compare our experiment, we have also computed energy bands, density of states, electron momentum densities and Compton profiles of α- and β-phases of GeTe using the linear combination of atomic orbitals method. The electron momentum density is found to play a major role in understanding the topology of bands in the vicinity of the Fermi level. It is seen that the density functional theory (DFT) with generalised gradient approximation is relatively in better agreement with the experiment than the local density approximation and hybrid Hartree-Fock/DFT.

Structure factor of blends of solvent-free nanoparticle-organic hybrid materials: density-functional theory and small angle X-ray scattering.

PubMed

Yu, Hsiu-Yu; Srivastava, Samanvaya; Archer, Lynden A; Koch, Donald L

2014-12-07

We investigate the static structure factor S(q) of solvent-free nanoparticle-organic hybrid materials consisting of silica nanocores and space-filling polyethylene glycol coronas using a density-functional theory and small angle X-ray scattering measurements. The theory considers a bidisperse suspension of hard spheres with different radii and tethered bead-spring oligomers with different grafting densities to approximate the polydispersity effects in experiments. The experimental systems studied include pure samples with different silica core volume fractions and the associated mean corona grafting densities, and blends with different mixing ratios of the pure samples, in order to introduce varying polydispersity of corona grafting density. Our scattering experiments and theory show that, compared to the hard-sphere suspension with the same core volume fraction, S(q) for pure samples exhibit both substantially smaller values at small q and stronger particle correlations corresponding to a larger effective hard core at large q, indicating that the tethered incompressible oligomers enforce a more uniform particle distribution, and the densely grafted brush gives rise to an additional exclusionary effect between the nanoparticles. According to the theory, polydispersity in the oligomer grafting density controls the deviation of S(q) from the monodisperse system at smaller q, and the interplay of the enhanced effective core size and the entropic attraction among the particles is responsible for complex variations in the particle correlations at larger q. The successful comparison between the predictions and the measurements for the blends further suggests that S(q) can be used to assess the uniformity of grafting density in polymer-grafted nanoparticle materials.

Physical properties of coir and pineapple leaf fibre reinforced polylactic acid hybrid composites

NASA Astrophysics Data System (ADS)

Siakeng, R.; Jawaid, M.; Ariffin, H.; Sapuan, S. M.

2018-01-01

This study examined the physical behaviour of Coir fibres (CF)/Pineapple leaf fibres (PALF)/Poly lactic acid (PLA) composites. In this research, coir and PALF reinforced PLA hybrid composites were fabricated by hand lay-up process and hot press. The aim of this work is to do comparative study on density, water absorption (WA) and thickness swelling (TS) of untreated CF/PALF reinforced PLA composites and hybrid composites. The effect of different fibre ratios in hybridization on density, WA and TS of CF/PALF hybrid composites were also analyzed and C7P3 showed highest density while P30 had lowest. The results indicated that the density varies on different fibre ratio. WA and TS of CF/PALF composites and hybrid composites vary with fibres ratio and soaking duration. WA and TS of untreated CF/PALF hybrid composites were increased by increasing coir fibre ratio so, C30 showed highest WA and TS whereas P30 and C1P1 showed least WA and TS respectively apart from neat PLA.

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

Tumuluru, Jaya Shankar; McCulloch, Richard Chet James

In this work a new hybrid genetic algorithm was developed which combines a rudimentary adaptive steepest ascent hill climbing algorithm with a sophisticated evolutionary algorithm in order to optimize complex multivariate design problems. By combining a highly stochastic algorithm (evolutionary) with a simple deterministic optimization algorithm (adaptive steepest ascent) computational resources are conserved and the solution converges rapidly when compared to either algorithm alone. In genetic algorithms natural selection is mimicked by random events such as breeding and mutation. In the adaptive steepest ascent algorithm each variable is perturbed by a small amount and the variable that caused the mostmore » improvement is incremented by a small step. If the direction of most benefit is exactly opposite of the previous direction with the most benefit then the step size is reduced by a factor of 2, thus the step size adapts to the terrain. A graphical user interface was created in MATLAB to provide an interface between the hybrid genetic algorithm and the user. Additional features such as bounding the solution space and weighting the objective functions individually are also built into the interface. The algorithm developed was tested to optimize the functions developed for a wood pelleting process. Using process variables (such as feedstock moisture content, die speed, and preheating temperature) pellet properties were appropriately optimized. Specifically, variables were found which maximized unit density, bulk density, tapped density, and durability while minimizing pellet moisture content and specific energy consumption. The time and computational resources required for the optimization were dramatically decreased using the hybrid genetic algorithm when compared to MATLAB's native evolutionary optimization tool.« less

Implementation and benchmark of a long-range corrected functional in the density functional based tight-binding method

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

Lutsker, V.; Niehaus, T. A., E-mail: thomas.niehaus@physik.uni-regensburg.de; Aradi, B.

2015-11-14

Bridging the gap between first principles methods and empirical schemes, the density functional based tight-binding method (DFTB) has become a versatile tool in predictive atomistic simulations over the past years. One of the major restrictions of this method is the limitation to local or gradient corrected exchange-correlation functionals. This excludes the important class of hybrid or long-range corrected functionals, which are advantageous in thermochemistry, as well as in the computation of vibrational, photoelectron, and optical spectra. The present work provides a detailed account of the implementation of DFTB for a long-range corrected functional in generalized Kohn-Sham theory. We apply themore » method to a set of organic molecules and compare ionization potentials and electron affinities with the original DFTB method and higher level theory. The new scheme cures the significant overpolarization in electric fields found for local DFTB, which parallels the functional dependence in first principles density functional theory (DFT). At the same time, the computational savings with respect to full DFT calculations are not compromised as evidenced by numerical benchmark data.« less

Application of hybrid supercapacitor using granule Li4Ti5O12/activated carbon with variation of current density

NASA Astrophysics Data System (ADS)

Lee, Byung-Gwan; Lee, Seung-Hwan

2017-03-01

We report the electrochemical performance of asymmetric hybrid supercapacitors composed of granule Li4Ti5O12 as an anode and activated carbon as a cathode with different current densities. It is demonstrated that the hybrid supercapacitors show good initial discharge capacities were ranged from 39.8 to 46.4 F g-1 in the current densities range of 0.3-1 A g-1. The performance degradation is proportional to the current density due to quick gassing, resulting from H2O and HF formation. In particular, the hybrid supercapacitors show the pretty good cycling stability of 97.4%, even at the high current density of 0.8 A g-1, which are among most important performance in the real application for energy storage devices. Therefore, we believe that hybrid supercapacitors using granule Li4Ti5O12/activated carbon are eligible for the promising next generation energy devices.

Computationally Probing the Performance of Hybrid, Heterogeneous, and Homogeneous Iridium-Based Catalysts for Water Oxidation

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

García-Melchor, Max; Vilella, Laia; López, Núria

2016-04-29

An attractive strategy to improve the performance of water oxidation catalysts would be to anchor a homogeneous molecular catalyst on a heterogeneous solid surface to create a hybrid catalyst. The idea of this combined system is to take advantage of the individual properties of each of the two catalyst components. We use Density Functional Theory to determine the stability and activity of a model hybrid water oxidation catalyst consisting of a dimeric Ir complex attached on the IrO 2(110) surface through two oxygen atoms. We find that homogeneous catalysts can be bound to its matrix oxide without losing significant activity.more » Hence, designing hybrid systems that benefit from both the high tunability of activity of homogeneous catalysts and the stability of heterogeneous systems seems feasible.« less

Exchange interaction between the triplet exciton and the localized spin in copper-phthalocyanine

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

Wu, Wei, E-mail: wei.wu@ucl.ac.uk

2014-06-14

Triplet excitonic state in the organic molecule may arise from a singlet excitation and the following inter-system crossing. Especially for a spin-bearing molecule, an exchange interaction between the triplet exciton and the original spin on the molecule can be expected. In this paper, such exchange interaction in copper-phthalocyanine (CuPc, spin-1/2 ) was investigated from first-principles by using density-functional theory within a variety of approximations to the exchange correlation, ranging from local-density approximation to long-range corrected hybrid-exchange functional. The magnitude of the computed exchange interaction is in the order of meV with the minimum value (1.5 meV, ferromagnetic) given by themore » long-range corrected hybrid-exchange functional CAM-B3LYP. This exchange interaction can therefore give rise to a spin coherence with an oscillation period in the order of picoseconds, which is much shorter than the triplet lifetime in CuPc (typically tens of nanoseconds). This implies that it might be possible to manipulate the localized spin on Cu experimentally using optical excitation and inter-system crossing well before the triplet state disappears.« less

Electronic structure properties of UO2 as a Mott insulator

NASA Astrophysics Data System (ADS)

Sheykhi, Samira; Payami, Mahmoud

2018-06-01

In this work using the density functional theory (DFT), we have studied the structural, electronic and magnetic properties of uranium dioxide with antiferromagnetic 1k-, 2k-, and 3k-order structures. Ordinary approximations in DFT, such as the local density approximation (LDA) or generalized gradient approximation (GGA), usually predict incorrect metallic behaviors for this strongly correlated electron system. Using Hubbard term correction for f-electrons, LDA+U method, as well as using the screened Heyd-Scuseria-Ernzerhof (HSE) hybrid functional for the exchange-correlation (XC), we have obtained the correct ground-state behavior as an insulator, with band gaps in good agreement with experiment.

Fragment-based {sup 13}C nuclear magnetic resonance chemical shift predictions in molecular crystals: An alternative to planewave methods

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

Hartman, Joshua D.; Beran, Gregory J. O., E-mail: gregory.beran@ucr.edu; Monaco, Stephen

2015-09-14

We assess the quality of fragment-based ab initio isotropic {sup 13}C chemical shift predictions for a collection of 25 molecular crystals with eight different density functionals. We explore the relative performance of cluster, two-body fragment, combined cluster/fragment, and the planewave gauge-including projector augmented wave (GIPAW) models relative to experiment. When electrostatic embedding is employed to capture many-body polarization effects, the simple and computationally inexpensive two-body fragment model predicts both isotropic {sup 13}C chemical shifts and the chemical shielding tensors as well as both cluster models and the GIPAW approach. Unlike the GIPAW approach, hybrid density functionals can be used readilymore » in a fragment model, and all four hybrid functionals tested here (PBE0, B3LYP, B3PW91, and B97-2) predict chemical shifts in noticeably better agreement with experiment than the four generalized gradient approximation (GGA) functionals considered (PBE, OPBE, BLYP, and BP86). A set of recommended linear regression parameters for mapping between calculated chemical shieldings and observed chemical shifts are provided based on these benchmark calculations. Statistical cross-validation procedures are used to demonstrate the robustness of these fits.« less

A Novel Strategy for Numerical Simulation of High-speed Turbulent Reacting Flows

NASA Technical Reports Server (NTRS)

Sheikhi, M. R. H.; Drozda, T. G.; Givi, P.

2003-01-01

The objective of this research is to improve and implement the filtered mass density function (FDF) methodology for large eddy simulation (LES) of high-speed reacting turbulent flows. We have just completed Year 1 of this research. This is the Final Report on our activities during the period: January 1, 2003 to December 31, 2003. 2002. In the efforts during the past year, LES is conducted of the Sandia Flame D, which is a turbulent piloted nonpremixed methane jet flame. The subgrid scale (SGS) closure is based on the scalar filtered mass density function (SFMDF) methodology. The SFMDF is basically the mass weighted probability density function (PDF) of the SGS scalar quantities. For this flame (which exhibits little local extinction), a simple flamelet model is used to relate the instantaneous composition to the mixture fraction. The modelled SFMDF transport equation is solved by a hybrid finite-difference/Monte Carlo scheme.

Spin-polarized density-matrix functional theory of the single-impurity Anderson model

NASA Astrophysics Data System (ADS)

Töws, W.; Pastor, G. M.

2012-12-01

Lattice density functional theory (LDFT) is used to investigate spin excitations in the single-impurity Anderson model. In this method, the single-particle density matrix γijσ with respect to the lattice sites replaces the wave function as the basic variable of the many-body problem. A recently developed two-level approximation (TLA) to the interaction-energy functional W[γ] is extended to systems having spin-polarized density distributions and bond orders. This allows us to investigate the effect of external magnetic fields and, in particular, the important singlet-triplet gap ΔE, which determines the Kondo temperature. Applications to finite Anderson rings and square lattices show that the gap ΔE as well as other ground-state and excited-state properties are very accurately reproduced. One concludes that the spin-polarized TLA is reliable in all interaction regimes, from weak to strong correlations, for different hybridization strengths and for all considered impurity valence states. In this way the efficiency of LDFT to account for challenging electron-correlation effects is demonstrated.

E2 and SN2 Reactions of X(-) + CH3CH2X (X = F, Cl); an ab Initio and DFT Benchmark Study.

PubMed

Bento, A Patrícia; Solà, Miquel; Bickelhaupt, F Matthias

2008-06-01

We have computed consistent benchmark potential energy surfaces (PESs) for the anti-E2, syn-E2, and SN2 pathways of X(-) + CH3CH2X with X = F and Cl. This benchmark has been used to evaluate the performance of 31 popular density functionals, covering local-density approximation, generalized gradient approximation (GGA), meta-GGA, and hybrid density-functional theory (DFT). The ab initio benchmark has been obtained by exploring the PESs using a hierarchical series of ab initio methods [up to CCSD(T)] in combination with a hierarchical series of Gaussian-type basis sets (up to aug-cc-pVQZ). Our best CCSD(T) estimates show that the overall barriers for the various pathways increase in the order anti-E2 (X = F) < SN2 (X = F) < SN2 (X = Cl) ∼ syn-E2 (X = F) < anti-E2 (X = Cl) < syn-E2 (X = Cl). Thus, anti-E2 dominates for F(-) + CH3CH2F, and SN2 dominates for Cl(-) + CH3CH2Cl, while syn-E2 is in all cases the least favorable pathway. Best overall agreement with our ab initio benchmark is obtained by representatives from each of the three categories of functionals, GGA, meta-GGA, and hybrid DFT, with mean absolute errors in, for example, central barriers of 4.3 (OPBE), 2.2 (M06-L), and 2.0 kcal/mol (M06), respectively. Importantly, the hybrid functional BHandH and the meta-GGA M06-L yield incorrect trends and qualitative features of the PESs (in particular, an erroneous preference for SN2 over the anti-E2 in the case of F(-) + CH3CH2F) even though they are among the best functionals as measured by their small mean absolute errors of 3.3 and 2.2 kcal/mol in reaction barriers. OLYP and B3LYP have somewhat higher mean absolute errors in central barriers (5.6 and 4.8 kcal/mol, respectively), but the error distribution is somewhat more uniform, and as a consequence, the correct trends are reproduced.

Probabilistic distribution and stochastic P-bifurcation of a hybrid energy harvester under colored noise

NASA Astrophysics Data System (ADS)

Mokem Fokou, I. S.; Nono Dueyou Buckjohn, C.; Siewe Siewe, M.; Tchawoua, C.

2018-03-01

In this manuscript, a hybrid energy harvesting system combining piezoelectric and electromagnetic transduction and subjected to colored noise is investigated. By using the stochastic averaging method, the stationary probability density functions of amplitudes are obtained and reveal interesting dynamics related to the long term behavior of the device. From stationary probability densities, we discuss the stochastic bifurcation through the qualitative change which shows that noise intensity, correlation time and other system parameters can be treated as bifurcation parameters. Numerical simulations are made for a comparison with analytical findings. The Mean first passage time (MFPT) is numerical provided in the purpose to investigate the system stability. By computing the Mean residence time (TMR), we explore the stochastic resonance phenomenon; we show how it is related to the correlation time of colored noise and high output power.

Hybridization wave as the cause of the metal-insulator transition in rare earth nickelates

NASA Astrophysics Data System (ADS)

Park, Hyowon; Marianetti, Chris A.; Millis, Andrew J.

2012-02-01

The metal-insulator transition driven by varying rare earth (Re) ion in ReNiO3 has been a longstanding challenge to materials theory. Experimental evidence suggesting charge order is seemingly incompatible with the strong Mott-Hubbard correlations characteristic of transition metals. We present density functional, Hartree-Fock and Dynamical Mean field calculations showing that the origin of the insulating phase is a hybridization wave, in which a two sublattice ordering of the oxygen breathing mode produces two Ni sites with almost identical Ni d-charge densities but very different magnetic moments and other properties. The high temperature crystal structure associated with smaller Re ions such as Lu is shown to be more susceptible to the distortion than the high temperature structure associated with larger Re ions such as La.

Extension of many-body theory and approximate density functionals to fractional charges and fractional spins.

PubMed

Yang, Weitao; Mori-Sánchez, Paula; Cohen, Aron J

2013-09-14

The exact conditions for density functionals and density matrix functionals in terms of fractional charges and fractional spins are known, and their violation in commonly used functionals has been shown to be the root of many major failures in practical applications. However, approximate functionals are designed for physical systems with integer charges and spins, not in terms of the fractional variables. Here we develop a general framework for extending approximate density functionals and many-electron theory to fractional-charge and fractional-spin systems. Our development allows for the fractional extension of any approximate theory that is a functional of G(0), the one-electron Green's function of the non-interacting reference system. The extension to fractional charge and fractional spin systems is based on the ensemble average of the basic variable, G(0). We demonstrate the fractional extension for the following theories: (1) any explicit functional of the one-electron density, such as the local density approximation and generalized gradient approximations; (2) any explicit functional of the one-electron density matrix of the non-interacting reference system, such as the exact exchange functional (or Hartree-Fock theory) and hybrid functionals; (3) many-body perturbation theory; and (4) random-phase approximations. A general rule for such an extension has also been derived through scaling the orbitals and should be useful for functionals where the link to the Green's function is not obvious. The development thus enables the examination of approximate theories against known exact conditions on the fractional variables and the analysis of their failures in chemical and physical applications in terms of violations of exact conditions of the energy functionals. The present work should facilitate the calculation of chemical potentials and fundamental bandgaps with approximate functionals and many-electron theories through the energy derivatives with respect to the fractional charge. It should play an important role in developing accurate approximate density functionals and many-body theory.

Exploring N-Rich Phases in Li(x)N(y) Clusters for Hydrogen Storage at Nanoscale.

PubMed

Bhattacharya, Amrita; Bhattacharya, Saswata

2015-09-17

We have performed cascade genetic algorithm and ab initio atomistic thermodynamics under the framework of first-principles-based hybrid density functional theory to study the (meta-)stability of a wide range of Li(x)N(y) clusters. We found that hybrid xc-functional is essential to address this problem as a local/semilocal functional simply fails even to predict a qualitative prediction. Most importantly, we find that though in bulk lithium nitride, the Li-rich phase, that is, Li3N, is the stable stoichiometry; in small Li(x)N(y) clusters, N-rich phases are more stable at thermodynamic equilibrium. We further show that these N-rich clusters are promising hydrogen storage material because of their easy adsorption and desorption ability at respectively low (≤300 K) and moderately high temperature (≥600 K).

Screened Hybrid and DFT + U Studies of the Structural, Electronic, and Optical Properties of U3O8

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

Wen, Xiaodong; Martin, Richard L.; Scuseria, Gustavo E.

2012-11-26

A systematic comparison of the structures and electronic and optical properties of U3O8 in the c2mm, P¯62m, and P21/m structures (the α, β, and γ phases, respectively) is performed using density functional theory + U (PBE + U) and the Heyd–Scuseria–Ernzerhof screened hybrid functional (HSE). The relationship between the semiconducting C2mm phase of U3O8 and the high temperature, metallic P¯62m phase is explored in more detail. Our calculated results show that the HSE functional gives a better description of the electronic and optical properties when compared with available experimental data for the α and β phases, but neither approach doesmore » particularly well for the high pressure γ phase.« less

Origin of photovoltage in perovskite solar cells probed by first-principles calculations

NASA Astrophysics Data System (ADS)

Echeverría-Arrondo, C.

2018-06-01

Hybrid halide perovskite solar cells hold great potential for photovoltaic applications, but suffer, however, from anomalous current density-voltage characteristics. With a view to further understanding the performance of these optoelectronic devices, we investigate a prototypical electron selective contact with density functional theory methods. Our computations on a TiO2/CH3NH3PbI3 heterojunction doped with Schottky defects at open circuit reveal a consistent picture of ions and interlayer excitons at the origin of photovoltage formation.

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.

Hierarchical Coupling of First-Principles Molecular Dynamics with Advanced Sampling Methods.

PubMed

Sevgen, Emre; Giberti, Federico; Sidky, Hythem; Whitmer, Jonathan K; Galli, Giulia; Gygi, Francois; de Pablo, Juan J

2018-05-14

We present a seamless coupling of a suite of codes designed to perform advanced sampling simulations, with a first-principles molecular dynamics (MD) engine. As an illustrative example, we discuss results for the free energy and potential surfaces of the alanine dipeptide obtained using both local and hybrid density functionals (DFT), and we compare them with those of a widely used classical force field, Amber99sb. In our calculations, the efficiency of first-principles MD using hybrid functionals is augmented by hierarchical sampling, where hybrid free energy calculations are initiated using estimates obtained with local functionals. We find that the free energy surfaces obtained from classical and first-principles calculations differ. Compared to DFT results, the classical force field overestimates the internal energy contribution of high free energy states, and it underestimates the entropic contribution along the entire free energy profile. Using the string method, we illustrate how these differences lead to different transition pathways connecting the metastable minima of the alanine dipeptide. In larger peptides, those differences would lead to qualitatively different results for the equilibrium structure and conformation of these molecules.

Optical properties of hybrid spherical nanoclusters containing quantum emitters and metallic nanoparticles

NASA Astrophysics Data System (ADS)

Yannopapas, V.; Paspalakis, E.

2018-05-01

We study theoretically the optical response of a hybrid spherical cluster containing quantum emitters and metallic nanoparticles. The quantum emitters are modeled as two-level quantum systems whose dielectric function is obtained via a density matrix approach wherein the modified spontaneous emission decay rate at the position of each quantum emitter is calculated via the electromagnetic Green's tensor. The problem of light scattering off the hybrid cluster is solved by employing the coupled-dipole method. We find, in particular, that the presence of the quantum emitters in the cluster, even in small fractions, can significantly alter the absorption and extinction spectra of the sole cluster of the metallic nanoparticles, where the corresponding electromagnetic modes can have a weak plexcitonic character under suitable conditions.

Hybrid-PIC Modeling of the Transport of Atomic Boron in a Hall Thruster

NASA Technical Reports Server (NTRS)

Smith, Brandon D.; Boyd, Iaian D.; Kamhawi, Hani

2015-01-01

Computational analysis of the transport of boron eroded from the walls of a Hall thruster is performed by implementing sputter yields of hexagonal boron nitride and velocity distribution functions of boron within the hybrid-PIC model HPHall. The model is applied to simulate NASA's HiVHAc Hall thruster at a discharge voltage of 500V and discharge powers of 1-3 kW. The number densities of ground- and 4P-state boron are computed. The density of ground-state boron is shown to be a factor of about 30 less than the plasma density. The density of the excited state is shown to be about three orders of magnitude less than that of the ground state, indicating that electron impact excitation does not significantly affect the density of ground-state boron in the discharge channel or near-field plume of a Hall thruster. Comparing the rates of excitation and ionization suggests that ionization has a greater influence on the density of ground-state boron, but is still negligible. The ground-state boron density is then integrated and compared to cavity ring-down spectroscopy (CRDS) measurements for each operating point. The simulation results show good agreement with the measurements for all operating points and provide evidence in support of CRDS as a tool for measuring Hall thruster erosion in situ.

Nano-sized Mo- and Nb-doped TiO2 as anode materials for high energy and high power hybrid Li-ion capacitors.

PubMed

Bauer, Dustin; Roberts, Alexander J; Matsumi, Noriyoshi; Darr, Jawwad A

2017-05-12

Nano-sized Mo-doped titania (Mo 0.1 Ti 0.9 O 2 ) and Nb-doped titania (Nb 0.25 Ti 0.75 O 2 ) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer-Emmett-Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO 2 negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5-3.0 V, the Mo 0.1 Ti 0.9 O 2 /AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg -1 at a power of 180 W kg -1 with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb 0.25 Ti 0.75 O 2 /AC hybrid supercapacitor maintained its energy density of 45 Wh kg -1 at 180 W kg -1 better, showing 36 Wh g -1 at 3200 W kg -1 , which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0-3.0 V led to an increase in power density, with the Mo 0.1 Ti 0.9 O 2 /AC hybrid supercapacitor giving energy densities of 12 Wh kg -1 and 2.5 Wh kg -1 at power densities of 6700 W kg -1 and 14 000 W kg -1 , respectively.

Nano-sized Mo- and Nb-doped TiO2 as anode materials for high energy and high power hybrid Li-ion capacitors

NASA Astrophysics Data System (ADS)

Bauer, Dustin; Roberts, Alexander J.; Matsumi, Noriyoshi; Darr, Jawwad A.

2017-05-01

Nano-sized Mo-doped titania (Mo0.1Ti0.9O2) and Nb-doped titania (Nb0.25Ti0.75O2) were directly synthesized via a continuous hydrothermal flow synthesis process. Materials characterization was conducted using physical techniques such as transmission electron microscopy, powder x-ray diffraction, x-ray photoelectron spectroscopy, Brunauer-Emmett-Teller specific surface area measurements and energy dispersive x-ray spectroscopy. Hybrid Li-ion supercapacitors were made with either a Mo-doped or Nb-doped TiO2 negative electrode material and an activated carbon (AC) positive electrode. Cells were evaluated using electrochemical testing (cyclic voltammetry, constant charge discharge cycling). The hybrid Li-ion capacitors showed good energy densities at moderate power densities. When cycled in the potential window 0.5-3.0 V, the Mo0.1Ti0.9O2/AC hybrid supercapacitor showed the highest energy densities of 51 Wh kg-1 at a power of 180 W kg-1 with energy densities rapidly declining with increasing applied specific current. In comparison, the Nb0.25Ti0.75O2/AC hybrid supercapacitor maintained its energy density of 45 Wh kg-1 at 180 W kg-1 better, showing 36 Wh g-1 at 3200 W kg-1, which is a very promising mix of high energy and power densities. Reducing the voltage window to the range 1.0-3.0 V led to an increase in power density, with the Mo0.1Ti0.9O2/AC hybrid supercapacitor giving energy densities of 12 Wh kg-1 and 2.5 Wh kg-1 at power densities of 6700 W kg-1 and 14 000 W kg-1, respectively.

Graphene hybridization for energy storage applications.

PubMed

Li, Xianglong; Zhi, Linjie

2018-05-08

Graphene has attracted considerable attention due to its unique two-dimensional structure, high electronic mobility, exceptional thermal conductivity, excellent optical transmittance, good mechanical strength, and ultrahigh surface area. To meet the ever increasing demand for portable electronic products, electric vehicles, smart grids, and renewable energy integrations, hybridizing graphene with various functions and components has been demonstrated to be a versatile and powerful strategy to significantly enhance the performance of various energy storage systems such as lithium-ion batteries, supercapacitors and beyond, because such hybridization can result in synergistic effects that combine the best merits of involved components and confer new functions and properties, thereby improving the charge/discharge efficiencies and capabilities, energy/power densities, and cycle life of these energy storage systems. This review will focus on diverse graphene hybridization principles and strategies for energy storage applications, and the proposed outline is as follows. First, graphene and its fundamental properties, followed by graphene hybrids and related hybridization motivation, are introduced. Second, the developed hybridization formulas of using graphene for lithium-ion batteries are systematically categorized from the viewpoint of material structure design, bulk electrode construction, and material/electrode collaborative engineering; the latest representative progress on anodes and cathodes of lithium-ion batteries will be reviewed following such classifications. Third, similar hybridization formulas for graphene-based supercapacitor electrodes will be summarized and discussed as well. Fourth, the recently emerging hybridization formulas for other graphene-based energy storage devices will be briefed in combination with typical examples. Finally, future prospects and directions on the exploration of graphene hybridization toward the design and construction of viable, high-class, and even newly-featured (e.g., flexible) energy storage materials, electrodes, and systems will be presented.

Controlled preparation of carbon nanotube-iron oxide nanoparticle hybrid materials by a modified wet impregnation method

NASA Astrophysics Data System (ADS)

Tsoufis, Τheodoros; Douvalis, Alexios P.; Lekka, Christina E.; Trikalitis, Pantelis N.; Bakas, Thomas; Gournis, Dimitrios

2013-09-01

We report a novel, simple, versatile, and reproducible approach for the in situ synthesis of iron oxide nanoparticles (NP) on the surface of carbon nanotubes (CNT). Chemically functionalized single- or multi-wall CNT were used as nanotemplates for the synthesis of a range of very small (<10 nm) ferrimagnetic and/or anti-ferromagnetic iron oxide NP on their surface. For the synthesis of the hybrid materials, we employed for the first time a modified wet impregnation method involving the adsorption of ferric cations (as nanoparticle's precursor) on the functionalized nanotube surface and the subsequent interaction with acetic acid vapors followed by calcination at 400 °C under different atmospheres (air, argon, and oxygen). X-ray diffraction, transmission electron microscopy, Mössbauer spectroscopy, and magnetization measurements were used to study in-detail the morphology, size, and type of crystalline phases in the resulting hybrid materials. In addition, Raman measurements were used to monitor possible structural changes of the nanotubes during the synthetic approach. The experimental results were further supported by density functional theory calculations. These calculations were also used to disclose, how the type of the carbon nanotube template affects the nature and the size of the resulting NP in the final hybrids.

FeP(Im)–AB Bonding Energies Evaluated with A Large Number of Density Functionals (P = porphine, Im = imidazole, AB = CO, NO, and O2)

PubMed Central

Liao, Meng-Sheng; Huang, Ming-Ju; Watts, John D.

2011-01-01

Sixty-four (64) density functionals, ranging from GGA, meta-GGA, hybrid GGA to hybrid meta-GGA, were tested to evaluate the FeP(Im)-AB bonding energies (Ebond) in the heme model complexes FeP(Im)(AB) (P = porphine, Im = imidazole, AB = CO, NO, and O2). The results indicate that an accurate prediction of Ebond for the various ligands to heme is difficult with the DFT methods; usually a functional successful for one system does not perform equally well for the other system(s). Relatively satisfactory results for the various FeP(Im)-AB bonding energies are obtained with the meta-GGA funtionals BLAP3 and Bmτ1; they yield Ebond values of ca.1.1, 1.2, and 0.4 eV for AB = CO, NO, and O2, respectively, which are in reasonable agreement with experimental data (0.78 – 0.85 eV for CO, 0.99 eV for NO, and 0.44 – 0.53 eV for O2). The other functionals show more or less deficiency for one or two of the systems. The performances of the various functionals in describing the spin-state energetics of the five-coordinate FeP(Im) complex were also examined. PMID:22228914

DFT STUDY OF THE HYDROLYSIS OF SOME S-TRIAZINES

EPA Science Inventory

The acid-catalyzed hydrolysis of atrazine and related 2-chloro-s-triazines to the corresponding 2-hydroxy-s-triazines was investigated using the B3LYP hybrid density functional theory method. Gas-phase calculations were performed at the B3LYP/6-311++G(d,p)//B3LYP/6-31G* level of ...

Effects of B site doping on electronic structures of InNbO4 based on hybrid density functional calculations

NASA Astrophysics Data System (ADS)

Lu, M. F.; Zhou, C. P.; Li, Q. Q.; Zhang, C. L.; Shi, H. F.

2018-01-01

In order to improve the photocatalytic activity under visible-light irradiation, we adopted first principle calculations based on density functional theory (DFT) to calculate the electronic structures of B site transition metal element doped InNbO4. The results indicated that the complete hybridization of Nb 4d states and some Ti 3d states contributed to the new conduction band of Ti doped InNbO4, barely changing the position of band edge. For Cr doping, some localized Cr 3d states were introduced into the band gap. Nonetheless, the potential of localized levels was too positive to cause visible-light reaction. When it came to Cu doping, the band gap was almost same with that of InNbO4 as well as some localized Cu 3d states appeared above the top of VB. The introduction of localized energy levels benefited electrons to migrate from valence band (VB) to conduction band (CB) by absorbing lower energy photons, realizing visible-light response.

Optimization of self-catalyzed InAs Nanowires on flexible graphite for photovoltaic infrared photodetectors

PubMed Central

Anyebe, Ezekiel A.; Sandall, I.; Jin, Z. M.; Sanchez, Ana M.; Rajpalke, Mohana K.; Veal, Timothy D.; Cao, Y. C.; Li, H. D.; Harvey, R.; Zhuang, Q. D.

2017-01-01

The recent discovery of flexible graphene monolayers has triggered extensive research interest for the development of III-V/graphene functional hybrid heterostructures. In order to fully exploit their enormous potential in device applications, it is essential to optimize epitaxial growth for the precise control of nanowire geometry and density. Herein, we present a comprehensive growth study of InAs nanowires on graphitic substrates by molecular beam epitaxy. Vertically well-aligned and thin InAs nanowires with high yield were obtained in a narrow growth temperature window of 420–450 °C within a restricted domain of growth rate and V/III flux ratio. The graphitic substrates enable high nanowire growth rates, which is favourable for cost-effective device fabrication. A relatively low density of defects was observed. We have also demonstrated InAs-NWs/graphite heterojunction devices exhibiting rectifying behaviour. Room temperature photovoltaic response with a cut-off wavelength of 3.4 μm was demonstrated. This elucidates a promising route towards the monolithic integration of InAs nanowires with graphite for flexible and functional hybrid devices. PMID:28393845

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

NASA Astrophysics Data System (ADS)

Ferri, Nicola; Ambrosetti, Alberto; Tkatchenko, Alexandre

2017-07-01

Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. It is common to utilize electrostatics and Pauli pushback to control the interface electronic properties, while the ubiquitous van der Waals (vdW) interactions are often considered to have a negligible direct contribution (beyond the obvious structural relaxation). Here, we apply a fully self-consistent Tkatchenko-Scheffler vdW density functional to demonstrate that the weak vdW interactions can induce sizable charge rearrangements at hybrid metal/organic systems (HMOS). The complex vdW correlation potential smears out the interfacial electronic density, thereby reducing the charge transfer in HMOS, changes the interface work functions by up to 0.2 eV, and increases the interface dipole moment by up to 0.3 Debye. Our results suggest that vdW interactions should be considered as an additional control parameter in the design of hybrid interfaces with the desired electronic properties.

Non-aqueous hybrid supercapacitors fabricated with mesoporous TiO2 microspheres and activated carbon electrodes with superior performance

NASA Astrophysics Data System (ADS)

Cai, Yong; Zhao, Bote; Wang, Jie; Shao, Zongping

2014-05-01

Mesoporous TiO2 microspheres, synthesized by a facile template-free solvothermal method and subsequent heat treatment, are exploited as the electrode for hybrid supercapacitors. The effects of the calcination temperature on the phase composition, particulate microstructure and morphology are characterized by XRD, Raman, FE-SEM and N2 adsorption/desorption measurements. Hybrid supercapacitors utilizing the as-prepared TiO2 mesoporous microspheres as the negative electrode and activated carbon (AC) as the positive electrode in a non-aqueous electrolyte are fabricated. The electrochemical performance of these hybrid supercapacitors is studied by galvanostatic charge-discharge and cyclic voltammetry (CV). The hybrid supercapacitor built from TiO2 microspheres calcined at 400 °C shows the best performance, delivering an energy density of 79.3 Wh kg-1 at a power density of 178.1 W kg-1. Even at a power density of 9.45 kW kg-1, an energy density of 31.5 Wh kg-1 is reached. These values are much higher than the AC-AC symmetric supercapacitor. In addition, the hybrid supercapacitor exhibits excellent cycling performance, retaining 98% of the initial energy density after 1000 cycles. Such outstanding electrochemical performance of the hybrid supercapacitor is attributed to the matched reaction kinetics between the two electrodes with different energy storage mechanisms.

Density functional theory and chromium: Insights from the dimers

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

Würdemann, Rolf; Kristoffersen, Henrik H.; Moseler, Michael

2015-03-28

The binding in small Cr clusters is re-investigated, where the correct description of the dimer in three charge states is used as criterion to assign the most suitable density functional theory approximation. The difficulty in chromium arises from the subtle interplay between energy gain from hybridization and energetic cost due to exchange between s and d based molecular orbitals. Variations in published bond lengths and binding energies are shown to arise from insufficient numerical representation of electron density and Kohn-Sham wave-functions. The best functional performance is found for gradient corrected (GGA) functionals and meta-GGAs, where we find severe differences betweenmore » functionals from the same family due to the importance of exchange. Only the “best fit” from Bayesian error estimation is able to predict the correct energetics for all three charge states unambiguously. With this knowledge, we predict small bond-lengths to be exclusively present in Cr{sub 2} and Cr{sub 2}{sup −}. Already for the dimer cation, solely long bond-lengths appear, similar to what is found in the trimer and in chromium bulk.« less

Three-dimensional Nitrogen-Doped Graphene Supported Molybdenum Disulfide Nanoparticles as an Advanced Catalyst for Hydrogen Evolution Reaction

PubMed Central

Dong, Haifeng; Liu, Conghui; Ye, Haitao; Hu, Linping; Fugetsu, Bunshi; Dai, Wenhao; Cao, Yu; Qi, Xueqiang; Lu, Huiting; Zhang, Xueji

2015-01-01

An efficient three-dimensional (3D) hybrid material of nitrogen-doped graphene sheets (N-RGO) supporting molybdenum disulfide (MoS2) nanoparticles with high-performance electrocatalytic activity for hydrogen evolution reaction (HER) is fabricated by using a facile hydrothermal route. Comprehensive microscopic and spectroscopic characterizations confirm the resulting hybrid material possesses a 3D crumpled few-layered graphene network structure decorated with MoS2 nanoparticles. Electrochemical characterization analysis reveals that the resulting hybrid material exhibits efficient electrocatalytic activity toward HER under acidic conditions with a low onset potential of 112 mV and a small Tafel slope of 44 mV per decade. The enhanced mechanism of electrocatalytic activity has been investigated in detail by controlling the elemental composition, electrical conductance and surface morphology of the 3D hybrid as well as Density Functional Theory (DFT) calculations. This demonstrates that the abundance of exposed active sulfur edge sites in the MoS2 and nitrogen active functional moieties in N-RGO are synergistically responsible for the catalytic activity, whilst the distinguished and coherent interface in MoS2/N-RGO facilitates the electron transfer during electrocatalysis. Our study gives insights into the physical/chemical mechanism of enhanced HER performance in MoS2/N-RGO hybrids and illustrates how to design and construct a 3D hybrid to maximize the catalytic efficiency. PMID:26639026

Entanglement in Quantum-Classical Hybrid

NASA Technical Reports Server (NTRS)

Zak, Michail

2011-01-01

It is noted that the phenomenon of entanglement is not a prerogative of quantum systems, but also occurs in other, non-classical systems such as quantum-classical hybrids, and covers the concept of entanglement as a special type of global constraint imposed upon a broad class of dynamical systems. Application of hybrid systems for physics of life, as well as for quantum-inspired computing, has been outlined. In representing the Schroedinger equation in the Madelung form, there is feedback from the Liouville equation to the Hamilton-Jacobi equation in the form of the quantum potential. Preserving the same topology, the innovators replaced the quantum potential with other types of feedback, and investigated the property of these hybrid systems. A function of probability density has been introduced. Non-locality associated with a global geometrical constraint that leads to an entanglement effect was demonstrated. Despite such a quantum like characteristic, the hybrid can be of classical scale and all the measurements can be performed classically. This new emergence of entanglement sheds light on the concept of non-locality in physics.

Solar powered hybrid sensor module program

NASA Technical Reports Server (NTRS)

Johnson, J. M.; Holmes, H. K.

1985-01-01

Geo-orbital systems of the near future will require more sophisticated electronic and electromechanical monitoring and control systems than current satellite systems with an emphasis in the design on the electronic density and autonomy of the subsystem components. Results of a project to develop, design, and implement a proof-of-concept sensor system for space applications, with hybrids forming the active subsystem components are described. The design of the solar power hybrid sensor modules is discussed. Module construction and function are described. These modules combined low power CMOS electronics, GaAs solar cells, a crystal oscillatory standard UART data formatting, and a bidirectional optical data link into a single 1.25 x 1.25 x 0.25 inch hybrid package which has no need for electrical input or output. Several modules were built and tested. Applications of such a system for future space missions are also discussed.

Lower Hybrid Oscillations in Multicomponent Space Plasmas Subjected to Ion Cyclotron Waves

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Krivorutsky, E. N.; Moore, T. E.; Liemohn, M. W.; Horwitz, J. L.

1997-01-01

It is found that in multicomponent plasmas subjected to Alfven or fast magnetosonic waves, such as are observed in regions of the outer plasmasphere and ring current-plasmapause overlap, lower hybrid oscillations are generated. The addition of a minor heavy ion component to a proton-electron plasma significantly lowers the low-frequency electric wave amplitude needed for lower hybrid wave excitation. It is found that the lower hybrid wave energy density level is determined by the nonlinear process of induced scattering by ions and electrons; hydrogen ions in the region of resonant velocities are accelerated; and nonresonant particles are weakly heated due to the induced scattering. For a given example, the light resonant ions have an energy gain factor of 20, leading to the development of a high-energy tail in the H(+) distribution function due to low-frequency waves.

All 2D materials as electrodes for high power hybrid energy storage applications

NASA Astrophysics Data System (ADS)

Kato, Keiko; Sayed, Farheen N.; Babu, Ganguli; Ajayan, Pulickel M.

2018-04-01

Achieving both high energy and power densities from energy storage devices is a core strategy to meet the increasing demands of high performance portable electronics and electric transportation systems. Li-ion capacitor is a promising hybrid technology that strategically exploits high energy density from a Li-ion battery electrode and high power density from a supercapacitor electrode. However, the performance and safety of hybrid devices are still major concerns due to the use of graphite anodes which form passivation layers with organic electrolytes at lower potentials. Here, we explore 2D nanosheets as both anode and cathode electrodes to build a high power system without compromising energy density. Owing to the high electrical conductivity and multivalent redox activity at higher potentials, the Li-ion intercalation electrode is capable of maintaining large energy density at higher current rates with less safety risk than conventional systems. Hybrid devices consisting of all in all 2D electrodes deliver energy density as high as 121 Wh g-1 (at 240 W kg-1) and retains 29 Wh g-1 at high power density of 3600 W kg-1.

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

Song, Jong-Won; Hirao, Kimihiko

Long-range corrected density functional theory (LC-DFT) attracts many chemists’ attentions as a quantum chemical method to be applied to large molecular system and its property calculations. However, the expensive time cost to evaluate the long-range HF exchange is a big obstacle to be overcome to be applied to the large molecular systems and the solid state materials. Upon this problem, we propose a linear-scaling method of the HF exchange integration, in particular, for the LC-DFT hybrid functional.

Superhydrophobic hybrid membranes by grafting arc-like macromolecular bridges on graphene sheets: Synthesis, characterization and properties

NASA Astrophysics Data System (ADS)

Mo, Zhao-Hua; Luo, Zheng; Huang, Qiang; Deng, Jian-Ping; Wu, Yi-Xian

2018-05-01

Grafting single end-tethered polymer chains on the surface of graphene is a conventional way to modify the surface properties of graphene oxide. However, grafting arc-like macromolecular bridges on graphene surfaces has been barely reported. Herein, a novel arc-like polydimethylsiloxane (PDMS) macromolecular bridges grafted graphene sheets (GO-g-Arc PDMS) was successfully synthesized via a confined interface reaction at 90 °C. Both the hydrophilic α- and ω-amino groups of linear hydrophobic NH2-PDMS-NH2 macromolecular chains rapidly reacted with epoxy and carboxyl groups on the surfaces of graphene oxide in water suspension to form arc-like PDMS macromolecular bridges on graphene sheets. The grafting density of arc-like PDMS bridges on graphene sheets can reach up to 0.80 mmol g-1 or 1.32 arc-like bridges per nm2 by this confined interface reaction. The water contact angle (WCA) of the hybrid membrane could be increased with increasing both the grafting density and content of covalent arc-like bridges architecture. The superhydrophobic hybrid membrane with a WCA of 153.4° was prepared by grinding of the above arc-like PDMS bridges grafted graphene hybrid, dispersing in ethanol and filtrating by organic filter membrane. This superhydrophobic hybrid membrane shows good self-cleaning and complete oil-water separation properties, which provides potential applications in anticontamination coating and oil-water separation. To the best of our knowledge, this is the first report on the synthesis of functional hybrid membranes by grafting arc-like PDMS macromolecular bridges on graphene sheets via a confined interface reaction.

Stability of Hydrocarbons of the Polyhedrane Family: Convergence of ab Initio Calculations and Corresponding Assessment of DFT Main Approximations.

PubMed

Sancho-García, J C

2011-09-13

Highly accurate coupled-cluster (CC) calculations with large basis sets have been performed to study the binding energy of the (CH)12, (CH)16, (CH)20, and (CH)24 polyhedral hydrocarbons in two, cage-like and planar, forms. We also considered the effect of other minor contributions: core-correlation, relativistic corrections, and extrapolations to the limit of the full CC expansion. Thus, chemically accurate values could be obtained for these complicated systems. These nearly exact results are used to evaluate next the performance of main approximations (i.e., pure, hybrid, and double-hybrid methods) within density functional theory (DFT) in a systematic fashion. Some commonly used functionals, including the B3LYP model, are affected by large errors, and only those having reduced self-interaction error (SIE), which includes the last family of conjectured expressions (double hybrids), are able to achieve reasonable low deviations of 1-2 kcal/mol especially when an estimate for dispersion interactions is also added.

Stretchable and semitransparent conductive hybrid hydrogels for flexible supercapacitors.

PubMed

Hao, Guang-Ping; Hippauf, Felix; Oschatz, Martin; Wisser, Florian M; Leifert, Annika; Nickel, Winfried; Mohamed-Noriega, Nasser; Zheng, Zhikun; Kaskel, Stefan

2014-07-22

Conductive polymers showing stretchable and transparent properties have received extensive attention due to their enormous potential in flexible electronic devices. Here, we demonstrate a facile and smart strategy for the preparation of structurally stretchable, electrically conductive, and optically semitransparent polyaniline-containing hybrid hydrogel networks as electrode, which show high-performances in supercapacitor application. Remarkably, the stability can extend up to 35,000 cycles at a high current density of 8 A/g, because of the combined structural advantages in terms of flexible polymer chains, highly interconnected pores, and excellent contact between the host and guest functional polymer phase.

Probabilistic assessment of uncertain adaptive hybrid composites

NASA Technical Reports Server (NTRS)

Shiao, Michael C.; Singhal, Surendra N.; Chamis, Christos C.

1994-01-01

Adaptive composite structures using actuation materials, such as piezoelectric fibers, were assessed probabilistically utilizing intraply hybrid composite mechanics in conjunction with probabilistic composite structural analysis. Uncertainties associated with the actuation material as well as the uncertainties in the regular (traditional) composite material properties were quantified and considered in the assessment. Static and buckling analyses were performed for rectangular panels with various boundary conditions and different control arrangements. The probability density functions of the structural behavior, such as maximum displacement and critical buckling load, were computationally simulated. The results of the assessment indicate that improved design and reliability can be achieved with actuation material.

Unraveling orbital hybridization of triplet emitters at the metal-organic interface.

PubMed

Ewen, Pascal R; Sanning, Jan; Doltsinis, Nikos L; Mauro, Matteo; Strassert, Cristian A; Wegner, Daniel

2013-12-27

We have investigated the structural and electronic properties of phosphorescent planar platinum(II) complexes at the interface of Au(111) with submolecular resolution using combined scanning tunneling microscopy and spectroscopy as well as density functional theory. Our analysis shows that molecule-substrate coupling and lateral intermolecular interactions are weak. While the ligand orbitals remain essentially unchanged upon contact with the substrate, we found modified electronic behavior at the Pt atom due to local hybridization and charge transfer to the substrate. Thus, this novel class of phosphorescent molecules exhibits well-defined and tunable interaction with its local environment.

Development of sugar palm yarn/glass fibre reinforced unsaturated polyester hybrid composites

NASA Astrophysics Data System (ADS)

Nurazzi, N. Mohd; Khalina, A.; Sapuan, S. Mohd; Rahmah, M.

2018-04-01

This study investigates the effect of fibre hybridization for sugar palm yarn fibre with glass fibre reinforced with unsaturated polyester composites. In this work, unsaturated polyester resin are reinforced with fibre at a ratio of 70:30 wt% and 60:40 wt%. The hybrid composites were characterized in terms of physical (density and water absorption), mechanical (tensile, flexural and compression) and thermal properties through thermal gravimetry analysis (TGA). Density determination showed that density increased with higher wt% of glass fibre. The inherently higher density of glass fibre increased the density of hybrid composite. Resistance to water absorption is improved upon the incorporation of glass fibre and the hybrid composites were found to reach equilibrium absorption at days 4 and 5. As for mechanical performance, the highest tensile strength, tensile modulus, flexural strength, flexural modulus and compression strength were obtained from 40 wt% of fibres reinforcement with ratio of 50:50 wt% of sugar palm yarn fibre and glass fibre reinforced unsaturated polyester composites. The increase of glass fibre loading had a synergistic effect on the mechanical properties to the composites structure due to its superior strength and modulus. The thermal stability of hybrid composites was improved by the increase of onset temperature and the reduction of residues upon increase in temperature.

Tailoring the electronic structure of β-Ga2O3 by non-metal doping from hybrid density functional theory calculations.

PubMed

Guo, Weiyan; Guo, Yating; Dong, Hao; Zhou, Xin

2015-02-28

A systematic study using density functional theory has been performed for β-Ga2O3 doped with non-metal elements X (X = C, N, F, Si, P, S, Cl, Se, Br, and I) to evaluate the effect of doping on the band edges and photocatalytic activity of β-Ga2O3. The utilization of a more reliable hybrid density functional, as prescribed by Heyd, Scuseria and Ernzerhof, is found to be effective in predicting the band gap of β-Ga2O3 (4.5 eV), in agreement with the experimental result (4.59 eV). Based on the relaxed structures of X-doped systems, the defect formation energies and the plots of density of states have been calculated to analyze the band edges, the band gap states and the preferred doping sites. Our results show that the doping is energetically favored under Ga-rich growth conditions with respect to O-rich growth conditions. It is easier to replace the threefold coordinated O atom with non-metal elements compared to the fourfold coordinated O atom. X-doped systems (X = C, Si, P) show no change in the band gap, with the presence of discrete midgap states, which have adverse effect on the photocatalytic properties. The photocatalytic redox ability can be improved to a certain extent by doping with N, S, Cl, Se, Br, and I. The band alignments for Se-doped and I-doped β-Ga2O3 are well positioned for the feasibility of both photo-oxidation and photo-reduction of water, which are promising photocatalysts for water splitting in the visible region.

On the accuracy of van der Waals inclusive density-functional theory exchange-correlation functionals for ice at ambient and high pressures.

PubMed

Santra, Biswajit; Klimes, Jirí; Tkatchenko, Alexandre; Alfè, Dario; Slater, Ben; Michaelides, Angelos; Car, Roberto; Scheffler, Matthias

2013-10-21

Density-functional theory (DFT) has been widely used to study water and ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on ice Ih and six proton ordered phases of ice. Consistent with our previous study [B. Santra, J. Klimeš, D. Alfè, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition pressures of the high-pressure ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high pressures remains and we suggest that because of the stern test the high pressure ice phases pose they should be used in future benchmark studies of simulation methods for water.

Short-range density functional correlation within the restricted active space CI method

NASA Astrophysics Data System (ADS)

Casanova, David

2018-03-01

In the present work, I introduce a hybrid wave function-density functional theory electronic structure method based on the range separation of the electron-electron Coulomb operator in order to recover dynamic electron correlations missed in the restricted active space configuration interaction (RASCI) methodology. The working equations and the computational algorithm for the implementation of the new approach, i.e., RAS-srDFT, are presented, and the method is tested in the calculation of excitation energies of organic molecules. The good performance of the RASCI wave function in combination with different short-range exchange-correlation functionals in the computation of relative energies represents a quantitative improvement with respect to the RASCI results and paves the path for the development of RAS-srDFT as a promising scheme in the computation of the ground and excited states where nondynamic and dynamic electron correlations are important.

Molecular Excitation Energies from Time-Dependent Density Functional Theory Employing Random-Phase Approximation Hessians with Exact Exchange.

PubMed

Heßelmann, Andreas

2015-04-14

Molecular excitation energies have been calculated with time-dependent density-functional theory (TDDFT) using random-phase approximation Hessians augmented with exact exchange contributions in various orders. It has been observed that this approach yields fairly accurate local valence excitations if combined with accurate asymptotically corrected exchange-correlation potentials used in the ground-state Kohn-Sham calculations. The inclusion of long-range particle-particle with hole-hole interactions in the kernel leads to errors of 0.14 eV only for the lowest excitations of a selection of three alkene, three carbonyl, and five azabenzene molecules, thus surpassing the accuracy of a number of common TDDFT and even some wave function correlation methods. In the case of long-range charge-transfer excitations, the method typically underestimates accurate reference excitation energies by 8% on average, which is better than with standard hybrid-GGA functionals but worse compared to range-separated functional approximations.

Identifying the distinct features of geometric structures for hole trapping to generate radicals on rutile TiO₂(110) in photooxidation using density functional theory calculations with hybrid functional.

PubMed

Wang, Dong; Wang, Haifeng; Hu, P

2015-01-21

Using density functional theory calculations with HSE 06 functional, we obtained the structures of spin-polarized radicals on rutile TiO2(110), which is crucial to understand the photooxidation at the atomic level, and further calculate the thermodynamic stabilities of these radicals. By analyzing the results, we identify the structural features for hole trapping in the system, and reveal the mutual effects among the geometric structures, the energy levels of trapped hole states and their hole trapping capacities. Furthermore, the results from HSE 06 functional are compared to those from DFT + U and the stability trend of radicals against the number of slabs is tested. The effect of trapped holes on two important steps of the oxygen evolution reaction, i.e. water dissociation and the oxygen removal, is investigated and discussed.

Modeling of the gate-controlled Kondo effect at carbon point defects in graphene

NASA Astrophysics Data System (ADS)

May, Daniel; Lo, Po-Wei; Deltenre, Kira; Henke, Anika; Mao, Jinhai; Jiang, Yuhang; Li, Guohong; Andrei, Eva Y.; Guo, Guang-Yu; Anders, Frithjof B.

2018-04-01

We study the magnetic properties in the vicinity of a single carbon defect in a monolayer of graphene. We include the unbound σ orbital and the vacancy-induced bound π state in an effective two-orbital single-impurity model. The local magnetic moments are stabilized by the Coulomb interaction as well as a significant ferromagnetic Hund's rule coupling between the orbitals predicted by a density functional theory calculation. A hybridization between the orbitals and the Dirac fermions is generated by the curvature of the graphene sheet in the vicinity of the vacancy. We present results for the local spectral function calculated using Wilson's numerical renormalization group approach for a realistic graphene band structure and find three different regimes depending on the filling, the controlling chemical potential, and the hybridization strength. These different regions are characterized by different magnetic properties. The calculated spectral functions qualitatively agree with recent scanning tunneling spectra on graphene vacancies.

Ionocovalency and Applications 1. Ionocovalency Model and Orbital Hybrid Scales

PubMed Central

Zhang, Yonghe

2010-01-01

Ionocovalency (IC), a quantitative dual nature of the atom, is defined and correlated with quantum-mechanical potential to describe quantitatively the dual properties of the bond. Orbiotal hybrid IC model scale, IC, and IC electronegativity scale, XIC, are proposed, wherein the ionicity and the covalent radius are determined by spectroscopy. Being composed of the ionic function I and the covalent function C, the model describes quantitatively the dual properties of bond strengths, charge density and ionic potential. Based on the atomic electron configuration and the various quantum-mechanical built-up dual parameters, the model formed a Dual Method of the multiple-functional prediction, which has much more versatile and exceptional applications than traditional electronegativity scales and molecular properties. Hydrogen has unconventional values of IC and XIC, lower than that of boron. The IC model can agree fairly well with the data of bond properties and satisfactorily explain chemical observations of elements throughout the Periodic Table. PMID:21151444

Hybrid Functional Study of Sodium and Potassium Incorporation in Cu2ZnSnS4

NASA Astrophysics Data System (ADS)

Tse, Kin Fai; Wong, Manhoi; Zhang, Yiou; Zhang, Jingzhao; Zhu, Junyi

The thermodynamics of Na and K incorporation and its effects in Cu2ZnSnS4 (CZTS) is studied using density functional theory with hybrid functional. The allowed chemical potential of Na/K in CZTS is established. Formation energy calculations shows that Na can be significantly incorporated as both substitutional defects and interstitial defects, and incorporation of K related defects are generally less favorable. Transition energy calculations is performed showing that both Na and K exhibit benign defect properties and act as a p-type dopant. The qualitative disagreement between GGA with rigid band edge shifting and HSE calculations, formation of defect complexes, and implications in experiment will also be discussed. The understandings on the defect properties of Na and K provides an essential knowledge to further understand the surfactant effects of Na and K observed in experiments. This work is supported by General Research Fund Ref. No: 14319416.

Functionalization of Polypyrrole Nanopipes with Redox-Active Polyoxometalates for High Energy Density Supercapacitors.

PubMed

Dubal, Deepak P; Ballesteros, Belén; Mohite, Ashwini A; Gómez-Romero, Pedro

2017-02-22

Hybrid materials are very attractive for the fabrication of high-performance supercapacitors. Here, we have explored organic-inorganic hybrid materials based on open-end porous 1 D polypyrrole nanopipes (PPy-NPipes) and heteropolyoxometalates (phosphotungstate ([PW 12 O 40 ] 3- , PW 12 ) or phosphomolybdate ([PMo 12 O 40 ] 3- , PMo 12 )) that display excellent areal capacitances. Two different hybrid materials (PMo 12 @PPy and PW 12 @PPy) were effectively synthesized and used for symmetric supercapacitors. The anchoring of the inorganic nanoclusters onto the conducting polymer nanopipes led to electrodes that stood up to our best expectations exhibiting outstanding areal capacitances that are almost 1.5 to 2 fold higher than that of pristine PPy-NPipes. In addition, symmetric cells based on PMo 12 @PPy and PW 12 @PPy hybrid electrodes were fabricated and showed significant improvement in cell performance with very high volumetric capacitances in the range of 6.3-6.8 F cm -3 (considering the volume of whole device). Indeed, they provide extended potential windows in acidic electrolytes (up to 1.5 V) which led to ultrahigh energy densities of 1.5 and 2.2 mWh cm -3 for PMo 12 @PPy and PW 12 @PPy cells, respectively. Thus, these unique organic-inorganic hybrid symmetric cells displayed extraordinary electrochemical performances far exceeding those of more complex asymmetric systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

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

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

2015-04-14

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

The Role of Structural Enthalpy in Spherical Nucleic Acid Hybridization.

PubMed

Fong, Lam-Kiu; Wang, Ziwei; Schatz, George C; Luijten, Erik; Mirkin, Chad A

2018-05-23

DNA hybridization onto DNA-functionalized nanoparticle surfaces (e.g., in the form of a spherical nucleic acid (SNA)) is known to be enhanced relative to hybridization free in solution. Surprisingly, via isothermal titration calorimetry, we reveal that this enhancement is enthalpically, as opposed to entropically, dominated by ∼20 kcal/mol. Coarse-grained molecular dynamics simulations suggest that the observed enthalpic enhancement results from structurally confining the DNA on the nanoparticle surface and preventing it from adopting enthalpically unfavorable conformations like those observed in the solution case. The idea that structural confinement leads to the formation of energetically more stable duplexes is evaluated by decreasing the degree of confinement a duplex experiences on the nanoparticle surface. Both experiment and simulation confirm that when the surface-bound duplex is less confined, i.e., at lower DNA surface density or at greater distance from the nanoparticle surface, its enthalpy of formation approaches the less favorable enthalpy of duplex formation for the linear strand in solution. This work provides insight into one of the most important and enabling properties of SNAs and will inform the design of materials that rely on the thermodynamics of hybridization onto DNA-functionalized surfaces, including diagnostic probes and therapeutic agents.

Sensitivity of the Properties of Ruthenium “Blue Dimer” to Method, Basis Set, and Continuum Model

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

Ozkanlar, Abdullah; Clark, Aurora E.

2012-05-23

The ruthenium “blue dimer” [(bpy)2RuIIIOH2]2O4+ is best known as the first well-defined molecular catalyst for water oxidation. It has been subject to numerous computational studies primarily employing density functional theory. However, those studies have been limited in the functionals, basis sets, and continuum models employed. The controversy in the calculated electronic structure and the reaction energetics of this catalyst highlights the necessity of benchmark calculations that explore the role of density functionals, basis sets, and continuum models upon the essential features of blue-dimer reactivity. In this paper, we report Kohn-Sham complete basis set (KS-CBS) limit extrapolations of the electronic structuremore » of “blue dimer” using GGA (BPW91 and BP86), hybrid-GGA (B3LYP), and meta-GGA (M06-L) density functionals. The dependence of solvation free energy corrections on the different cavity types (UFF, UA0, UAHF, UAKS, Bondi, and Pauling) within polarizable and conductor-like polarizable continuum model has also been investigated. The most common basis sets of double-zeta quality are shown to yield results close to the KS-CBS limit; however, large variations are observed in the reaction energetics as a function of density functional and continuum cavity model employed.« less

Efficient time-dependent density functional theory approximations for hybrid density functionals: analytical gradients and parallelization.

PubMed

Petrenko, Taras; Kossmann, Simone; Neese, Frank

2011-02-07

In this paper, we present the implementation of efficient approximations to time-dependent density functional theory (TDDFT) within the Tamm-Dancoff approximation (TDA) for hybrid density functionals. For the calculation of the TDDFT/TDA excitation energies and analytical gradients, we combine the resolution of identity (RI-J) algorithm for the computation of the Coulomb terms and the recently introduced "chain of spheres exchange" (COSX) algorithm for the calculation of the exchange terms. It is shown that for extended basis sets, the RIJCOSX approximation leads to speedups of up to 2 orders of magnitude compared to traditional methods, as demonstrated for hydrocarbon chains. The accuracy of the adiabatic transition energies, excited state structures, and vibrational frequencies is assessed on a set of 27 excited states for 25 molecules with the configuration interaction singles and hybrid TDDFT/TDA methods using various basis sets. Compared to the canonical values, the typical error in transition energies is of the order of 0.01 eV. Similar to the ground-state results, excited state equilibrium geometries differ by less than 0.3 pm in the bond distances and 0.5° in the bond angles from the canonical values. The typical error in the calculated excited state normal coordinate displacements is of the order of 0.01, and relative error in the calculated excited state vibrational frequencies is less than 1%. The errors introduced by the RIJCOSX approximation are, thus, insignificant compared to the errors related to the approximate nature of the TDDFT methods and basis set truncation. For TDDFT/TDA energy and gradient calculations on Ag-TB2-helicate (156 atoms, 2732 basis functions), it is demonstrated that the COSX algorithm parallelizes almost perfectly (speedup ~26-29 for 30 processors). The exchange-correlation terms also parallelize well (speedup ~27-29 for 30 processors). The solution of the Z-vector equations shows a speedup of ~24 on 30 processors. The parallelization efficiency for the Coulomb terms can be somewhat smaller (speedup ~15-25 for 30 processors), but their contribution to the total calculation time is small. Thus, the parallel program completes a Becke3-Lee-Yang-Parr energy and gradient calculation on the Ag-TB2-helicate in less than 4 h on 30 processors. We also present the necessary extension of the Lagrangian formalism, which enables the calculation of the TDDFT excited state properties in the frozen-core approximation. The algorithms described in this work are implemented into the ORCA electronic structure system.

Mulliken's populations and electron momentum densities of transition metal tungstates using LCAO scheme

NASA Astrophysics Data System (ADS)

Meena, B. S.; Heda, N. L.; Ahuja, B. L.

2018-05-01

We have computed the Mulliken's populations (MP) and electron momentum densities (EMDs) for TMWO4 (TM=Co, Ni, Cu and Zn) using linear combination of atomic orbitals (LCAO) scheme. The latest hybridization of Hartree-Fock (HF) and density functional theory (DFT) under the framework of LCAO approximations (so called WC1LYP and B1WC) have been employed. The theoretical EMDs have been compared with the available experimental data which show that WC1LYP scheme gives slightly better agreement with the experimental data for all the reported tungstates. Such trend shows the applicability of Lee-Yang-Parr (LYP) correlation energies within hybrid approximations in predicting the electronic properties of these compounds. Further, the MP data show the charge transfer from Co/Ni/Cu/Zn and W to O atoms. In addition, we have plotted the total EMDs at the same normalized area which show almost similar type of localization of 3d electrons (in real space) of Cu and Zn, which is lower than that of Ni and Co atoms in their tungstates environment.

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

NASA Astrophysics Data System (ADS)

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

2016-10-01

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

In search of a viable reaction pathway in the chelation of a metallo-protein

NASA Astrophysics Data System (ADS)

Rose, Frisco; Hodak, Miroslav; Bernholc, Jerry

2010-03-01

Misfolded metallo-proteins are potential causal agents in the onset of neuro-degenerative diseases, such as Alzheimer's and Parkinson's Diseases (PD). Experimental results involving metal chelation have shown significant promise in symptom reduction and misfolding reversal. We explore, through atomistic simulations, potential reaction pathways for the chelation of Cu^2+ from the metal binding site in our representation of a partially misfolded α-synuclein, the protein implicated in PD. Our ab initio simulations use Density Functional Theory (DFT) and nudged elastic band to obtain the minimized energy coordinates of this reaction. Our simulations include ab initio water at the interaction site and in its first solvation shells, while the remainder is fully solvated with orbital-free DFT water representation [1]. Our ongoing studies of viable chelation agents include nicotine, caffeine and other potential reagents, we will review the best case agents in this presentation. [4pt] [1] Hodak M, Lu W, Bernholc J. Hybrid ab initio Kohn-Sham density functional theory/frozen-density orbital-free density functional theory simulation method suitable for biological systems. J. Chem. Phys. 2008 Jan;128(1):014101-9.

Combining electronic structure and many-body theory with large databases: A method for predicting the nature of 4 f states in Ce compounds

NASA Astrophysics Data System (ADS)

Herper, H. C.; Ahmed, T.; Wills, J. M.; Di Marco, I.; Björkman, T.; Iuşan, D.; Balatsky, A. V.; Eriksson, O.

2017-08-01

Recent progress in materials informatics has opened up the possibility of a new approach to accessing properties of materials in which one assays the aggregate properties of a large set of materials within the same class in addition to a detailed investigation of each compound in that class. Here we present a large scale investigation of electronic properties and correlated magnetism in Ce-based compounds accompanied by a systematic study of the electronic structure and 4 f -hybridization function of a large body of Ce compounds. We systematically study the electronic structure and 4 f -hybridization function of a large body of Ce compounds with the goal of elucidating the nature of the 4 f states and their interrelation with the measured Kondo energy in these compounds. The hybridization function has been analyzed for more than 350 data sets (being part of the IMS database) of cubic Ce compounds using electronic structure theory that relies on a full-potential approach. We demonstrate that the strength of the hybridization function, evaluated in this way, allows us to draw precise conclusions about the degree of localization of the 4 f states in these compounds. The theoretical results are entirely consistent with all experimental information, relevant to the degree of 4 f localization for all investigated materials. Furthermore, a more detailed analysis of the electronic structure and the hybridization function allows us to make precise statements about Kondo correlations in these systems. The calculated hybridization functions, together with the corresponding density of states, reproduce the expected exponential behavior of the observed Kondo temperatures and prove a consistent trend in real materials. This trend allows us to predict which systems may be correctly identified as Kondo systems. A strong anticorrelation between the size of the hybridization function and the volume of the systems has been observed. The information entropy for this set of systems is about 0.42. Our approach demonstrates the predictive power of materials informatics when a large number of materials is used to establish significant trends. This predictive power can be used to design new materials with desired properties. The applicability of this approach for other correlated electron systems is discussed.

Rational construction of three dimensional hybrid Co3O4@NiMoO4 nanosheets array for energy storage application

NASA Astrophysics Data System (ADS)

Hong, Wei; Wang, Jinqing; Gong, Peiwei; Sun, Jinfeng; Niu, Lengyuan; Yang, Zhigang; Wang, Zhaofeng; Yang, Shengrong

2014-12-01

Electrodes with rationally designed hybrid nanostructures can offer many opportunities for the enhanced performance in electrochemical energy storage. In this work, the uniform 2D Co3O4-based building blocks have been prepared through a facile chemical etching assistant approach and a following treatment of thermal annealing. The obtained nanosheets array has been directly employed as 2D backbone for the subsequent construction of hybrid nanostructure of Co3O4@NiMoO4 by a simple hydrothermal synthesis. As a binder-free electrode, the constructed 3D hybrid nanostructures exhibit a high specific capacitance of 1526 F g-1 at a current density of 3 mA cm-2 and a capacitance retention of 72% with the increase of current density from 3 mA cm-2 to 30 mA cm-2. Moreover, an asymmetric supercapacitor based on this hybrid Co3O4@NiMoO4 and activated carbon can deliver a maximum energy density of 37.8 Wh kg-1 at a power density of 482 W kg-1. The outstanding electrochemical behaviors presented here suggest that this hybrid nanostructured material has potential applications in energy storage.

Development of braided rope seals for hypersonic engine applications. Part 2: Flow modeling

NASA Technical Reports Server (NTRS)

Mutharasan, Rajakkannu; Steinetz, Bruce M.; Tao, Xiaoming; Ko, Frank

1991-01-01

Two models based on the Kozeny-Carmen equation were developed to analyze the fluid flow through a new class of braided rope seals under development for advanced hypersonic engines. A hybrid seal geometry consisting of a braided sleeve and a substantial amount of longitudinal fibers with high packing density was selected for development based on its low leakage rates. The models developed allow prediction of the gas leakage rate as a function of fiber diameter, fiber packing density, gas properties, and pressure drop across the seal.

Engineering of a hybrid nanoparticle-based nicotine nanovaccine as a next-generation immunotherapeutic strategy against nicotine addiction: A focus on hapten density.

PubMed

Zhao, Zongmin; Powers, Kristen; Hu, Yun; Raleigh, Michael; Pentel, Paul; Zhang, Chenming

2017-04-01

Although vaccination is a promising way to combat nicotine addiction, most traditional hapten-protein conjugate nicotine vaccines only show limited efficacy due to their poor recognition and uptake by immune cells. This study aimed to develop a hybrid nanoparticle-based nicotine vaccine with improved efficacy. The focus was to study the impact of hapten density on the immunological efficacy of the proposed hybrid nanovaccine. It was shown that the nanovaccine nanoparticles were taken up by the dendritic cells more efficiently than the conjugate vaccine, regardless of the hapten density on the nanoparticles. At a similar hapten density, the nanovaccine induced a significantly stronger immune response against nicotine than the conjugate vaccine in mice. Moreover, the high- and medium-density nanovaccines resulted in significantly higher anti-nicotine antibody titers than their low-density counterpart. Specifically, the high-density nanovaccine exhibited better immunogenic efficacy, resulting in higher anti-nicotine antibody titers and lower anti-carrier protein antibody titers than the medium- and low-density versions. The high-density nanovaccine also had the best ability to retain nicotine in serum and to block nicotine from entering the brain. These results suggest that the hybrid nanoparticle-based nicotine vaccine can elicit strong immunogenicity by modulating the hapten density, thereby providing a promising next-generation immunotherapeutic strategy against nicotine addiction. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

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

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

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

Density-functional energy gaps of solids demystified

NASA Astrophysics Data System (ADS)

Perdew, John P.; Ruzsinszky, Adrienn

2018-06-01

The fundamental energy gap of a solid is a ground-state second energy difference. Can one find the fundamental gap from the gap in the band structure of Kohn-Sham density functional theory? An argument of Williams and von Barth (WB), 1983, suggests that one can. In fact, self-consistent band-structure calculations within the local density approximation or the generalized gradient approximation (GGA) yield the fundamental gap within the same approximation for the energy. Such a calculation with the exact density functional would yield a band gap that also underestimates the fundamental gap, because the exact Kohn-Sham potential in a solid jumps up by an additive constant when one electron is added, and the WB argument does not take this effect into account. The WB argument has been extended recently to generalized Kohn-Sham theory, the simplest way to implement meta-GGAs and hybrid functionals self-consistently, with an exchange-correlation potential that is a non-multiplication operator. Since this operator is continuous, the band gap is again the fundamental gap within the same approximation, but, because the approximations are more realistic, so is the band gap. What approximations might be even more realistic?

Communication: Correct charge transfer in CT complexes from the Becke'05 density functional

NASA Astrophysics Data System (ADS)

Becke, Axel D.; Dale, Stephen G.; Johnson, Erin R.

2018-06-01

It has been known for over twenty years that density functionals of the generalized-gradient approximation (GGA) type and exact-exchange-GGA hybrids with low exact-exchange mixing fraction yield enormous errors in the properties of charge-transfer (CT) complexes. Manifestations of this error have also plagued computations of CT excitation energies. GGAs transfer far too much charge in CT complexes. This error has therefore come to be called "delocalization" error. It remains, to this day, a vexing unsolved problem in density-functional theory (DFT). Here we report that a 100% exact-exchange-based density functional known as Becke'05 or "B05" [A. D. Becke, J. Chem. Phys. 119, 2972 (2003); 122, 064101 (2005)] predicts excellent charge transfers in classic CT complexes involving the electron donors NH3, C2H4, HCN, and C2H2 and electron acceptors F2 and Cl2. Our approach is variational, as in our recent "B05min" dipole moments paper [Dale et al., J. Chem. Phys. 147, 154103 (2017)]. Therefore B05 is not only an accurate DFT for thermochemistry but is promising as a solution to the delocalization problem as well.

The nature of excess electrons in anatase and rutile from hybrid DFT and RPA.

PubMed

Spreafico, Clelia; VandeVondele, Joost

2014-12-21

The behavior of excess electrons in undoped and defect free bulk anatase and rutile TiO2 has been investigated by state-of-the-art electronic structure methods including hybrid density functional theory (DFT) and the random phase approximation (RPA). Consistent with experiment, charge trapping and polaron formation is observed in both anatase and rutile. The difference in the anisotropic shape of the polarons is characterized, confirming for anatase the large polaron picture. For anatase, where polaron formation energies are small, charge trapping is observed also with standard hybrid functionals, provided the simulation cell is sufficiently large (864 atoms) to accommodate the lattice relaxation. Even though hybrid orbitals are required as a starting point for RPA in this system, the obtained polaron formation energies are relatively insensitive to the amount of Hartree-Fock exchange employed. The difference in trapping energy between rutile and anatase can be obtained accurately with both hybrid functionals and RPA. Computed activation energies for polaron hopping and delocalization clearly show that anatase and rutile might have different charge transport mechanisms. In rutile, only hopping is likely, whereas in anatase hopping and delocalization are competing. Delocalization will result in conduction-band-like and thus enhanced transport. Anisotropic conduction, in agreement with experimental data, is observed, and results from the tendency to delocalize in the [001] direction in rutile and the (001) plane in anatase. For future work, our calculations serve as a benchmark and suggest RPA on top on hybrid orbitals (PBE0 with 30% Hartree-Fock exchange), as a suitable method to study the rich chemistry and physics of TiO2.

Artificial plasma cusp generated by upper hybrid instabilities in HF heating experiments at HAARP

NASA Astrophysics Data System (ADS)

Kuo, Spencer; Snyder, Arnold

2013-05-01

High Frequency Active Auroral Research Program digisonde was operated in a fast mode to record ionospheric modifications by the HF heating wave. With the O mode heater of 3.2 MHz turned on for 2 min, significant virtual height spread was observed in the heater off ionograms, acquired beginning the moment the heater turned off. Moreover, there is a noticeable bump in the virtual height spread of the ionogram trace that appears next to the plasma frequency (~ 2.88 MHz) of the upper hybrid resonance layer of the HF heating wave. The enhanced spread and the bump disappear in the subsequent heater off ionograms recorded 1 min later. The height distribution of the ionosphere in the spread situation indicates that both electron density and temperature increases exceed 10% over a large altitude region (> 30 km) from below to above the upper hybrid resonance layer. This "mini cusp" (bump) is similar to the cusp occurring in daytime ionograms at the F1-F2 layer transition, indicating that there is a small ledge in the density profile reminiscent of F1-F2 layer transitions. Two parametric processes exciting upper hybrid waves as the sidebands by the HF heating waves are studied. Field-aligned purely growing mode and lower hybrid wave are the respective decay modes. The excited upper hybrid and lower hybrid waves introduce the anomalous electron heating which results in the ionization enhancement and localized density ledge. The large-scale density irregularities formed in the heat flow, together with the density irregularities formed through the parametric instability, give rise to the enhanced virtual height spread. The results of upper hybrid instability analysis are also applied to explain the descending feature in the development of the artificial ionization layers observed in electron cyclotron harmonic resonance heating experiments.

Accurate, precise, and efficient theoretical methods to calculate anion-π interaction energies in model structures.

PubMed

Mezei, Pál D; Csonka, Gábor I; Ruzsinszky, Adrienn; Sun, Jianwei

2015-01-13

A correct description of the anion-π interaction is essential for the design of selective anion receptors and channels and important for advances in the field of supramolecular chemistry. However, it is challenging to do accurate, precise, and efficient calculations of this interaction, which are lacking in the literature. In this article, by testing sets of 20 binary anion-π complexes of fluoride, chloride, bromide, nitrate, or carbonate ions with hexafluorobenzene, 1,3,5-trifluorobenzene, 2,4,6-trifluoro-1,3,5-triazine, or 1,3,5-triazine and 30 ternary π-anion-π' sandwich complexes composed from the same monomers, we suggest domain-based local-pair natural orbital coupled cluster energies extrapolated to the complete basis-set limit as reference values. We give a detailed explanation of the origin of anion-π interactions, using the permanent quadrupole moments, static dipole polarizabilities, and electrostatic potential maps. We use symmetry-adapted perturbation theory (SAPT) to calculate the components of the anion-π interaction energies. We examine the performance of the direct random phase approximation (dRPA), the second-order screened exchange (SOSEX), local-pair natural-orbital (LPNO) coupled electron pair approximation (CEPA), and several dispersion-corrected density functionals (including generalized gradient approximation (GGA), meta-GGA, and double hybrid density functional). The LPNO-CEPA/1 results show the best agreement with the reference results. The dRPA method is only slightly less accurate and precise than the LPNO-CEPA/1, but it is considerably more efficient (6-17 times faster) for the binary complexes studied in this paper. For 30 ternary π-anion-π' sandwich complexes, we give dRPA interaction energies as reference values. The double hybrid functionals are much more efficient but less accurate and precise than dRPA. The dispersion-corrected double hybrid PWPB95-D3(BJ) and B2PLYP-D3(BJ) functionals perform better than the GGA and meta-GGA functionals for the present test set.

Biosolar energy generation and harvesting from biomolecule-copolymer hybrid systems

NASA Astrophysics Data System (ADS)

Chu, Bong-Chieh Benjamin

Alternative energy sources have become an increasingly important topic as energy needs outpace supply. Furthermore, as the world moves into the digital age of portable electronics, highly efficient and lightweight energy sources will need to be developed. Current technology, such as lithium ion batteries, provide enough power to run portable electronics for hours or days, but can still allow for improvement in their power density (W/kg). Utilizing energy-transducing membrane proteins, which are by nature highly efficient, it is possible to engineer biological-based energy sources with energy densities far greater than any solid-state systems. Furthermore, solar powered membrane proteins have the added benefit of a virtually unlimited supply of energy. This work has developed protein-polymer hybrid films and nanoscale vesicles for a variety of applications from fuel-cell technology to biological-based photovoltaics. Bacteriorhodopsin (BR), a light-activated proton pump, and Cytochrome C Oxidase (COX), a protein involved in the electron transport chain in mitochondria, were reconstituted into biomimetic triblock copolymer membranes. Block copolymer membranes mimic the amphiphilic nature of a natural lipid bilayer but exhibit greater mechanical stability due to UV-polymerizable endgroups. In BR/COX functionalized nanovesicles, proton gradients generated by the light-activated proton pumping of BR are used to drive COX in reverse to generate electrons, providing a hybrid biologically-active polymer to convert solar energy to chemical energy, and finally to electrical energy. This work has found protein activity in planar membranes through the photoelectric current generation by BR and the proton pumping activity of BR-functionalized polymer membranes deposited onto proton exchange membranes, as well as the coupled functionality of BR and COX through current generation in cyclic voltammetry and direct current measurements. Current switching between light and dark environments of composite BR/COX polymer vesicles show a light-dependent current generation with current changes as high as 10muA. Furthermore, electrode modifications were made using polymer and polymer/carbon nanotube (CNT) coatings as anti-absorbent and conductive anti-absorbent layers for the purpose of a more robust electrode. These findings have shown that biological functionality can be engineered into synthetic polymers to make hybrid devices.

Comparative studies of the spectroscopy of CuCl2: DFT versus standard ab initio approaches

NASA Astrophysics Data System (ADS)

Ramírez-Solís, A.; Poteau, R.; Vela, A.; Daudey, J. P.

2005-04-01

The XΠg2-Σg +2, XΠg2-Δg2, XΠg2-Σu +2, XΠg2-Πu2 transitions on CuCl2 have been studied using several exchange-correlation functionals from the various types of density functional theory (DFT) approaches like local density approximation (LDA), generalized gradient approximation (GGA), hybrid and meta-GGA. The results are compared with the experience and with those coming from the most sophisticated nondynamic and dynamic electronic correlation treatments using the same relativistic effective core potentials and especially developed basis sets to study the electronic structure of the five lowest states and the corresponding vertical and adiabatic transition energies. The calculated transition energies for three of the hybrid functionals (B3LYP, B97-2, and PBE0) are in very good agreement with the benchmark ab initio results and experimental figures. All of the other functionals largely overestimate the XΠg2-Σg +2 and XΠg2-Δg2 transition energies, many of them even placing the Δg2 ligand field state above the charge transfer Πu2 and Σu +2 states. The relative weight of the Hartree-Fock exchange in the definition of the functional used appears to play a key role in the accurate description of the ΛSΣ density defined by the orientation of the 3d hole (σ, π, or δ) on Cu in the field of both chlorine atoms, but no simple connection of this weight with the quality of the spectra has been found. Mulliken charges and spin densities are carefully analyzed; a possible link between the extent of spin density on the metal for the XΠg2 state and the performance of the various functionals was observed, suggesting that those that lead to the largest values (close to 0.65) are the ones that best reproduce these four transitions. Most functionals lead to a remarkably low ionicity for the three ligand field states even for the best performing functionals, compared to the complete active space (SCF) (21, 14) ab initio values. These findings show that not only large variational ab initio calculations can produce reliable spectroscopic results for extremely complex systems where delicate electronic correlation effects have to be carefully dealt with. However, those functionals that were recently shown to perform best for a series of molecular properties [J. Chem. Phys. 121 3405 (2004)] are not the ones that produce the best transition energies for this complex case.

Hybrid k .p tight-binding model for intersubband optics in atomically thin InSe films

NASA Astrophysics Data System (ADS)

Magorrian, S. J.; Ceferino, A.; Zólyomi, V.; Fal'ko, V. I.

2018-04-01

We propose atomic films of n -doped γ -InSe as a platform for intersubband optics in the infrared and far-infrared range, coupled to out-of-plane polarized light. Depending on the film thickness (number of layers) and the amount of n -doping of the InSe film, these transitions span from ˜0.7 eV for bilayer to ˜0.05 eV for 15-layer InSe. We use a hybrid k .p theory and tight-binding model, fully parametrized using density-functional theory, to predict their oscillator strengths and thermal linewidths at room temperature.

Nanowire modified carbon fibers for enhanced electrical energy storage

NASA Astrophysics Data System (ADS)

Shuvo, Mohammad Arif Ishtiaque; (Bill) Tseng, Tzu-Liang; Ashiqur Rahaman Khan, Md.; Karim, Hasanul; Morton, Philip; Delfin, Diego; Lin, Yirong

2013-09-01

The study of electrochemical super-capacitors has become one of the most attractive topics in both academia and industry as energy storage devices because of their high power density, long life cycles, and high charge/discharge efficiency. Recently, there has been increasing interest in the development of multifunctional structural energy storage devices such as structural super-capacitors for applications in aerospace, automobiles, and portable electronics. These multifunctional structural super-capacitors provide structures combining energy storage and load bearing functionalities, leading to material systems with reduced volume and/or weight. Due to their superior materials properties, carbon fiber composites have been widely used in structural applications for aerospace and automotive industries. Besides, carbon fiber has good electrical conductivity which will provide lower equivalent series resistance; therefore, it can be an excellent candidate for structural energy storage applications. Hence, this paper is focused on performing a pilot study for using nanowire/carbon fiber hybrids as building materials for structural energy storage materials; aiming at enhancing the charge/discharge rate and energy density. This hybrid material combines the high specific surface area of carbon fiber and pseudo-capacitive effect of metal oxide nanowires, which were grown hydrothermally in an aligned fashion on carbon fibers. The aligned nanowire array could provide a higher specific surface area that leads to high electrode-electrolyte contact area thus fast ion diffusion rates. Scanning Electron Microscopy and X-Ray Diffraction measurements are used for the initial characterization of this nanowire/carbon fiber hybrid material system. Electrochemical testing is performed using a potentio-galvanostat. The results show that gold sputtered nanowire carbon fiber hybrid provides 65.9% higher energy density than bare carbon fiber cloth as super-capacitor.

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

Bisti, F.; Stroppa, A.; Picozzi, S.

The electronic structure of Croconic Acid in the condensed phase has been studied by comparing core level and valence band x-ray photoelectron spectroscopy experiments and first principles density functional theory calculations using the Heyd-Scuseria-Ernzerhof screened hybrid functional and the GW approximation. By exploring the photoemission spectra for different deposition thicknesses, we show how the formation of the hydrogen bond network modifies the O 1s core level lineshape. Moreover, the valence band can be explained only if the intermolecular interactions are taken into account in the theoretical approach.

Electrical and optical properties of Si-doped Ga2O3

NASA Astrophysics Data System (ADS)

Li, Yin; Yang, Chuanghua; Wu, Liyuan; Zhang, Ru

2017-05-01

The charge densities, band structure, density of states, dielectric functions of Si-doped β-Ga2O3 have been investigated based on the density functional theory (DFT) within the hybrid functional HSE06. The heavy doping makes conduction band split out more bands and further influences the band structure. It decreases the band gap and changes from a direct gap to an indirect gap. After doping, the top of the valence bands is mainly composed by the O-2p states, Si-3p states and Ga-4p states and the bottom of the conduction bands is almost formed by the Si-3s, Si-3p and Ga-4s orbits. The anisotropic optical properties have been investigated by means of the complex dielectric function. After the heavy Si doping, the position of absorption band edges did not change much. The slope of the absorption curve descends and indicates that the absorption became more slow for Si-doped β-Ga2O3 than undoped one due to the indirect gap of Si-doped β-Ga2O3.

Density functional theory study of bulk and single-layer magnetic semiconductor CrPS4

NASA Astrophysics Data System (ADS)

Zhuang, Houlong L.; Zhou, Jia

2016-11-01

Searching for two-dimensional (2D) materials with multifunctionality is one of the main goals of current research in 2D materials. Magnetism and semiconducting are certainly two desirable functional properties for a single 2D material. In line with this goal, here we report a density functional theory (DFT) study of bulk and single-layer magnetic semiconductor CrPS4. We find that the ground-state magnetic structure of bulk CrPS4 exhibits the A-type antiferromagnetic ordering, which transforms to ferromagnetic (FM) ordering in single-layer CrPS4. The calculated formation energy and phonon spectrum confirm the stability of single-layer CrPS4. The band gaps of FM single-layer CrPS4 calculated with a hybrid density functional are within the visible-light range. We also study the effects of FM ordering on the optical absorption spectra and band alignments for water splitting, indicating that single-layer CrPS4 could be a potential photocatalyst. Our work opens up ample opportunities of energy-related applications of single-layer CrPS4.

Computational Modeling of the Optical Rotation of Amino Acids: An "in Silico" Experiment for Physical Chemistry

ERIC Educational Resources Information Center

Simpson, Scott; Autschbach, Jochen; Zurek, Eva

2013-01-01

A computational experiment that investigates the optical activity of the amino acid valine has been developed for an upper-level undergraduate physical chemistry laboratory course. Hybrid density functional theory calculations were carried out for valine to confirm the rule that adding a strong acid to a solution of an amino acid in the l…

Singlet and triplet excitons and charge polarons in cycloparaphenylenes. A density functional theory study

DOE PAGES

Liu, Jin; Adamska, Lyudmyla; Doorn, Stephen K.; ...

2015-05-14

Conformational structure and the electronic properties of various electronic excitations in cycloparaphenylenes (CPPs) are calculated using hybrid Density Functional Theory (DFT). The results demonstrate that wavefunctions of singlet and triplet excitons as well as the positive and negative polarons remain fully delocalized in CPPs. In contrast, these excitations in larger CPP molecules become localized on several phenyl rings, which are locally planarized, while the undeformed ground state geometry is preserved on the rest of the hoop. As evidenced by the measurements of bond-length alternation and dihedral angles, localized regions show stronger hybridization between neighboring bonds and thus enhanced electronic communication.more » This effect is even more significant in the smaller hoops, where phenyl rings have strong quinoid character in the ground state. Thus, upon excitation, electron–phonon coupling leads to the self-trapping of the electronic wavefunction and release of energy from fractions of an eV up to two eVs, depending on the type of excitation and the size of the hoop. The impact of such localization on electronic and optical properties of CPPs is systematically investigated and compared with the available experimental measurements.« less

Electron band structure of the high pressure cubic phase of AlH3

NASA Astrophysics Data System (ADS)

Shi, Hongliang; Zarifi, Niliffar; Yim, Wai-Leung; Tse, J. S.

2012-07-01

The electronic band structure of the cubic Pm3n phase of AlH3 stable above 100 GPa is examined with semi-local, Tran-Blaha modified Becke-Johnson local density approximation (TB-mBJLDA), screened hybrid density functionals and GW methods. The shift of the conduction band to higher energy with increasing pressure is predicted by all methods. However, there are significant differences in detail band structure. In the pressure range from 90 to160 GPa, semi-local, hybrid functional and TB-mBJLDA calculations predicted that AlH3 is a poor metal. In comparison, GW calculations show a gap opening at 160 GPa and AlH3 becomes a small gap semi-conductor. From the trends of the calculated band shifts, it can be concluded that the favourable conditions leading to the nesting of Fermi surfaces predicted by semi-local calculation have disappeared if the exchange term is included. The results highlight the importance of the correction to the exchange energy on the band structure of hydrogen dominant dense metal hydrides at high pressure hydrides and may help to rationalize the absence of superconductivity in AlH3 from experimental measurements.

Large eddy simulations of a bluff-body stabilized hydrogen-methane jet flame

NASA Astrophysics Data System (ADS)

Drozda, Tomasz; Pope, Stephen

2005-11-01

Large eddy simulation (LES) is conducted of the turbulent bluff-body stabilized hydrogen-methane flame as considered in the experiments of the Combustion Research Facility at the Sandia National Laboratories and of the Thermal Research Group at the University of Sydney [1]. Both, reacting and non-reacting flows are considered. The subgrid scale (SGS) closure in LES is based on the scalar filtered mass density function (SFMDF) methodology [2]. A flamelet model is used to relate the chemical composition to the mixture fraction. The modeled SFMDF transport equation is solved by a hybrid finite-difference (FD) / Monte Carlo (MC) scheme. The FD component of the hybrid solver is validated by comparisons of the experimentally available flow statistics with those predicted by LES. The results via this method capture important features of the flames as observed experimentally.[1] A. R. Masri, R. W. Dibble, and R. S. Barlow. The structure of turbulent nonpremixed flames revealed by Raman-Rayleigh-LIF measurements. Prog. Energy Combust. Sci., 22:307--362, 1996. [2] F. A. Jaberi, P. J. Colucci, S. James, P. Givi, and S. B. Pope. Filtered mass density function for large eddy simulation of turbulent reacting flows. J. Fluid Mech., 401:85--121, 1999.

A One-Dimensional Organic Lead Chloride Hybrid with Excitation-Dependent Broadband Emissions

DOE PAGES

Wu, Guanhong; Zhou, Chenkun; Ming, Wenmei; ...

2018-05-23

Organic–inorganic metal halide hybrids have emerged as a new class of materials with fascinating optical and electronic properties. The exceptional structure tunability has enabled the development of materials with various dimensionalities at the molecular level, from three-dimensional (3D) to 2D, 1D, and 0D. Here, we report a new 1D lead chloride hybrid, C 4N 2H 14PbCl 4, which exhibits unusual inverse excitation-dependent broadband emission from bluish-green to yellow. Density functional theory calculations were performed to better understand the mechanism of this excitation-dependent broadband emission. This 1D hybrid material is found to have two emission centers, corresponding to the self-trapped excitonsmore » (STEs) and vacancy-bound excitons. The excitation-dependent emission is due to different populations of these two types of excitons generated at different excitation wavelengths. Furthermore, this work shows the rich chemistry and physics of organic–inorganic metal halide hybrids and paves the way to achieving novel light emitters with excitation-dependent broadband emissions at room temperature.« less

A One-Dimensional Organic Lead Chloride Hybrid with Excitation-Dependent Broadband Emissions

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

Wu, Guanhong; Zhou, Chenkun; Ming, Wenmei

Organic–inorganic metal halide hybrids have emerged as a new class of materials with fascinating optical and electronic properties. The exceptional structure tunability has enabled the development of materials with various dimensionalities at the molecular level, from three-dimensional (3D) to 2D, 1D, and 0D. Here, we report a new 1D lead chloride hybrid, C 4N 2H 14PbCl 4, which exhibits unusual inverse excitation-dependent broadband emission from bluish-green to yellow. Density functional theory calculations were performed to better understand the mechanism of this excitation-dependent broadband emission. This 1D hybrid material is found to have two emission centers, corresponding to the self-trapped excitonsmore » (STEs) and vacancy-bound excitons. The excitation-dependent emission is due to different populations of these two types of excitons generated at different excitation wavelengths. Furthermore, this work shows the rich chemistry and physics of organic–inorganic metal halide hybrids and paves the way to achieving novel light emitters with excitation-dependent broadband emissions at room temperature.« less

Simulations of Turbulent Momentum and Scalar Transport in Non-Reacting Confined Swirling Coaxial Jets

NASA Technical Reports Server (NTRS)

Shih, Tsan-Hsing; Liu, Nan-Suey; Moder, Jeffrey P.

2015-01-01

This paper presents the numerical simulations of confined three-dimensional coaxial water jets. The objectives are to validate the newly proposed nonlinear turbulence models of momentum and scalar transport, and to evaluate the newly introduced scalar APDF and DWFDF equation along with its Eulerian implementation in the National Combustion Code (NCC). Simulations conducted include the steady RANS, the unsteady RANS (URANS), and the time-filtered Navier-Stokes (TFNS); both without and with invoking the APDF or DWFDF equation. When the APDF (ensemble averaged probability density function) or DWFDF (density weighted filtered density function) equation is invoked, the simulations are of a hybrid nature, i.e., the transport equations of energy and species are replaced by the APDF or DWFDF equation. Results of simulations are compared with the available experimental data. Some positive impacts of the nonlinear turbulence models and the Eulerian scalar APDF and DWFDF approach are observed.

An Unscented Kalman-Particle Hybrid Filter for Space Object Tracking

NASA Astrophysics Data System (ADS)

Raihan A. V, Dilshad; Chakravorty, Suman

2018-03-01

Optimal and consistent estimation of the state of space objects is pivotal to surveillance and tracking applications. However, probabilistic estimation of space objects is made difficult by the non-Gaussianity and nonlinearity associated with orbital mechanics. In this paper, we present an unscented Kalman-particle hybrid filtering framework for recursive Bayesian estimation of space objects. The hybrid filtering scheme is designed to provide accurate and consistent estimates when measurements are sparse without incurring a large computational cost. It employs an unscented Kalman filter (UKF) for estimation when measurements are available. When the target is outside the field of view (FOV) of the sensor, it updates the state probability density function (PDF) via a sequential Monte Carlo method. The hybrid filter addresses the problem of particle depletion through a suitably designed filter transition scheme. To assess the performance of the hybrid filtering approach, we consider two test cases of space objects that are assumed to undergo full three dimensional orbital motion under the effects of J 2 and atmospheric drag perturbations. It is demonstrated that the hybrid filters can furnish fast, accurate and consistent estimates outperforming standard UKF and particle filter (PF) implementations.

The development of a new type of rechargeable batteries based on hybrid electrolytes.

PubMed

Zhou, Haoshen; Wang, Yonggang; Li, Huiqiao; He, Ping

2010-09-24

Lithium ion batteries (LIBs), which have the highest energy density among all currently available rechargeable batteries, have recently been considered for use in hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and pure electric vehicles (PEV). A major challenge in this effort is to increase the energy density of LIBs to satisfy the industrial needs of HEVs, PHEVs, and PEVs. Recently, new types of lithium-air and lithium-copper batteries that employ hybrid electrolytes have attracted significant attention; these batteries are expected to succeed lithium ion batteries as next-generation power sources. Herein, we review the concept of hybrid electrolytes, as well as their advantages and disadvantages. In addition, we examine new battery types that use hybrid electrolytes.

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.

Hybrid preconditioning for iterative diagonalization of ill-conditioned generalized eigenvalue problems in electronic structure calculations

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

Cai, Yunfeng, E-mail: yfcai@math.pku.edu.cn; Department of Computer Science, University of California, Davis 95616; Bai, Zhaojun, E-mail: bai@cs.ucdavis.edu

2013-12-15

The iterative diagonalization of a sequence of large ill-conditioned generalized eigenvalue problems is a computational bottleneck in quantum mechanical methods employing a nonorthogonal basis for ab initio electronic structure calculations. We propose a hybrid preconditioning scheme to effectively combine global and locally accelerated preconditioners for rapid iterative diagonalization of such eigenvalue problems. In partition-of-unity finite-element (PUFE) pseudopotential density-functional calculations, employing a nonorthogonal basis, we show that the hybrid preconditioned block steepest descent method is a cost-effective eigensolver, outperforming current state-of-the-art global preconditioning schemes, and comparably efficient for the ill-conditioned generalized eigenvalue problems produced by PUFE as the locally optimal blockmore » preconditioned conjugate-gradient method for the well-conditioned standard eigenvalue problems produced by planewave methods.« less

Electronegativity estimator built on QTAIM-based domains of the bond electron density.

PubMed

Ferro-Costas, David; Pérez-Juste, Ignacio; Mosquera, Ricardo A

2014-05-15

The electron localization function, natural localized molecular orbitals, and the quantum theory of atoms in molecules have been used all together to analyze the bond electron density (BED) distribution of different hydrogen-containing compounds through the definition of atomic contributions to the bonding regions. A function, gAH , obtained from those contributions is analyzed along the second and third periods of the periodic table. It exhibits periodic trends typically assigned to the electronegativity (χ), and it is also sensitive to hybridization variations. This function also shows an interesting S shape with different χ-scales, Allred-Rochow's being the one exhibiting the best monotonical increase with regard to the BED taken by each atom of the bond. Therefore, we think this χ can be actually related to the BED distribution. Copyright © 2014 Wiley Periodicals, Inc.

Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces.

PubMed

Asmuruf, Frans A; Besley, Nicholas A

2008-08-14

The near-edge x-ray absorption fine structure of benzene in the gas phase and adsorbed on the Au(111) and Pt(111) surfaces is studied with time dependent density functional theory. Excitation energies computed with hybrid exchange-correlation functionals are too low compared to experiment. However, after applying a constant shift the spectra are in good agreement with experiment. For benzene on the Au(111) surface, two bands arising from excitation to the e(2u)(pi(*)) and b(2g)(pi(*)) orbitals of benzene are observed for photon incidence parallel to the surface. On Pt(111) surface, a broader band arises from excitation to benzene orbitals that are mixed with the surface and have both sigma(*)(Pt-C) and pi(*) characters.

Study of electronic structure and Compton profiles of transition metal diborides

NASA Astrophysics Data System (ADS)

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

2017-08-01

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

Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory.

PubMed

Sissay, Adonay; Abanador, Paul; Mauger, François; Gaarde, Mette; Schafer, Kenneth J; Lopata, Kenneth

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagating the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.

Angle-dependent strong-field molecular ionization rates with tuned range-separated time-dependent density functional theory

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

Sissay, Adonay; Abanador, Paul; Mauger, François

2016-09-07

Strong-field ionization and the resulting electronic dynamics are important for a range of processes such as high harmonic generation, photodamage, charge resonance enhanced ionization, and ionization-triggered charge migration. Modeling ionization dynamics in molecular systems from first-principles can be challenging due to the large spatial extent of the wavefunction which stresses the accuracy of basis sets, and the intense fields which require non-perturbative time-dependent electronic structure methods. In this paper, we develop a time-dependent density functional theory approach which uses a Gaussian-type orbital (GTO) basis set to capture strong-field ionization rates and dynamics in atoms and small molecules. This involves propagatingmore » the electronic density matrix in time with a time-dependent laser potential and a spatial non-Hermitian complex absorbing potential which is projected onto an atom-centered basis set to remove ionized charge from the simulation. For the density functional theory (DFT) functional we use a tuned range-separated functional LC-PBE*, which has the correct asymptotic 1/r form of the potential and a reduced delocalization error compared to traditional DFT functionals. Ionization rates are computed for hydrogen, molecular nitrogen, and iodoacetylene under various field frequencies, intensities, and polarizations (angle-dependent ionization), and the results are shown to quantitatively agree with time-dependent Schrödinger equation and strong-field approximation calculations. This tuned DFT with GTO method opens the door to predictive all-electron time-dependent density functional theory simulations of ionization and ionization-triggered dynamics in molecular systems using tuned range-separated hybrid functionals.« less

Electrical potential-assisted DNA hybridization. How to mitigate electrostatics for surface DNA hybridization.

PubMed

Tymoczko, Jakub; Schuhmann, Wolfgang; Gebala, Magdalena

2014-12-24

Surface-confined DNA hybridization reactions are sensitive to the number and identity of DNA capture probes and experimental conditions such as the nature and the ionic strength of the electrolyte solution. When the surface probe density is high or the concentration of bulk ions is much lower than the concentration of ions within the DNA layer, hybridization is significantly slowed down or does not proceed at all. However, high-density DNA monolayers are attractive for designing high-sensitivity DNA sensors. Thus, circumventing sluggish DNA hybridization on such interfaces allows a high surface concentration of target DNA and improved signal/noise ratio. We present potential-assisted hybridization as a strategy in which an external voltage is applied to the ssDNA-modified interface during the hybridization process. Results show that a significant enhancement of hybridization can be achieved using this approach.

Generation of hybrid sinograms for the recovery of kV-CT images with metal artifacts for helical tomotherapy

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

Jeon, Hosang; Park, Dahl; Kim, Wontaek

Purpose: The overall goal of this study is to restore kilovoltage computed tomography (kV-CT) images which are disfigured by patients’ metal prostheses. By generating a hybrid sinogram that is a combination of kV and megavoltage (MV) projection data, the authors suggest a novel metal artifact-reduction (MAR) method that retains the image quality to match that of kV-CT and simultaneously restores the information of metal prostheses lost due to photon starvation. Methods: CT projection data contain information about attenuation coefficients and the total length of the attenuation. By normalizing raw kV projections with their own total lengths of attenuation, mean attenuationmore » projections were obtained. In the same manner, mean density projections of MV-CT were obtained by the normalization of MV projections resulting from the forward projection of density-calibrated MV-CT images with the geometric parameters of the kV-CT device. To generate the hybrid sinogram, metal-affected signals of the kV sinogram were identified and replaced by the corresponding signals of the MV sinogram following a density calibration step with kV data. Filtered backprojection was implemented to reconstruct the hybrid CT image. To validate the authors’ approach, they simulated four different scenarios for three heads and one pelvis using metallic rod inserts within a cylindrical phantom. Five inserts describing human body elements were also included in the phantom. The authors compared the image qualities among the kV, MV, and hybrid CT images by measuring the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), the densities of all inserts, and the spatial resolution. In addition, the MAR performance was compared among three existing MAR methods and the authors’ hybrid method. Finally, for clinical trials, the authors produced hybrid images of three patients having dental metal prostheses to compare their MAR performances with those of the kV, MV, and three existing MAR methods. Results: The authors compared the image quality and MAR performance of the hybrid method with those of other imaging modalities and the three MAR methods, respectively. The total measured mean of the CNR (SNR) values for the nonmetal inserts was determined to be 14.3 (35.3), 15.3 (37.8), and 25.5 (64.3) for the kV, MV, and hybrid images, respectively, and the spatial resolutions of the hybrid images were similar to those of the kV images. The measured densities of the metal and nonmetal inserts in the hybrid images were in good agreement with their true densities, except in cases of extremely low densities, such as air and lung. Using the hybrid method, major streak artifacts were suitably removed and no secondary artifacts were introduced in the resultant image. In clinical trials, the authors verified that kV and MV projections were successfully combined and turned into the resultant hybrid image with high image contrast, accurate metal information, and few metal artifacts. The hybrid method also outperformed the three existing MAR methods with regard to metal information restoration and secondary artifact prevention. Conclusions: The authors have shown that the hybrid method can restore the overall image quality of kV-CT disfigured by severe metal artifacts and restore the information of metal prostheses lost due to photon starvation. The hybrid images may allow for the improved delineation of structures of interest and accurate dose calculations for radiation treatment planning for patients with metal prostheses.« less

Ferrocene/fullerene hybrids showing large second-order nonlinear optical activities: impact of the cage unit size.

PubMed

Wang, Wen-Yong; Wang, Li; Ma, Na-Na; Zhu, Chang-Li; Qiu, Yong-Qing

2015-06-07

The electron donor-acceptor complexes, which undergo intramolecular charge transfer under external stimulus, are an emerging class of materials showing important application in nonlinear optics. Synthesizing ferrocene/fullerene complexes through face-to-face fusion would enjoy the merits of both ferrocene and fullerene due to their strong donor-acceptor interactions. Four ferrocene/fullerene hybrid complexes with the gradual extension of fullerene cage size, including CpFe(C60H5), CpFe(C66H5), CpFe(C70H5), and CpFe(C80H5) (Cp is cyclopentadienyl), have been investigated by density functional theory. These hybrid molecules give eclipsed and staggered isomers. The main reason that the eclipsed isomer is stable is that the eclipsed structure possesses large CpFefullerene bonding energy. The CpFefullerene interaction is smaller than that of CpFefullerene, which must come from two different interfaces. The presence of covalent bond character between CpFe and fullerene is supported by the localized orbital locator, deformation of electron density distribution and energy decomposition analysis. Significantly, the absorption bands and first hyperpolarizabilities of these hybrid complexes are strongly sensitive to the fullerene cage size, which is ascribed to a change in the charge transfer pattern, especially for CpFe(C80H5), which displays reverse π → π* charge transfer from bottom to top cage, leading to notable hyperpolarizability. Investigation of the structure-property relationship at the molecular level can benefit the design and preparation of such hybrid complexes in chemistry and materials science.

Post-silking Factor Consequences for N Efficiency Changes Over 38 Years of Commercial Maize Hybrids.

PubMed

Chen, Keru; Vyn, Tony J

2017-01-01

Hybrid selection in maize ( Zea mays L.) over the decades has increased post-silking dry matter (PostDM) and nitrogen (PostN) accumulation, often with an accompanying increase in one or more N use efficiency (NUE) metrics such as partial factor productivity (PFP), N conversion efficiency (NCE), and N internal efficiency (NIE). More certainty on the underlying mechanisms of how PostDM and PostN changes over time have contributed to NUE gains or losses in modern-era hybrids can only be realized by directly comparing hybrids of different eras in the context of production-system-relevant management systems. A two-year and two-location field study was conducted in Indiana with two N rates (55 and 220 kg N ha -1 ), three plant densities (54,000, 79,000, and 104,000 plants ha -1 ) and eight commercial hybrids that were released by a single seed company from 1967 to 2005. The main treatment effects of N rate, density, and hybrid dominated the PostDM and PostN responses, and there were no significant two-way or three-way interactions. Total dry matter at maturity gains averaged 80 kg ha -1 year -1 of hybrid release when averaged over locations, plant densities and N rates. Total N contents at maturity increased 0.68 kg ha -1 year -1 , primarily due to annual increases in grain N content (0.8 kg ha -1 year -1 ). Post-silking N uptake rate increased 0.44 kg ha -1 year -1 for these era hybrids in more favorable production site-years. Slopes of grain N concentration increases per unit PostN gain were similar for all hybrids. Gains in average PFP over time were considerably higher at the low N rate (0.9 kg ha -1 year -1 ) than at the high N rate (0.3 kg kg -1 year -1 ). Hybrid gains in NIE were evident from 1967 to 1994, but not thereafter. The low N rate and higher plant densities also increased relative NIE and NCE values, but without hybrid interactions. There was no consistent trend of NIE or NCE gains in these hybrids primarily because grain and whole-plant N concentrations didn't decline over the decades at either N rate, and because NIE and NCE were often plant-density dependent.

Surface chemistry of oxygen on aluminum--Performance of the density functionals: PBE, PBE0, M06, and M06-L.

PubMed

Lousada, Cláudio M; Korzhavyi, Pavel A

2016-04-05

We investigated the performance of the density functional theory (DFT) functionals PBE, PBE0, M06, and M06-L for describing the molecular and dissociative adsorption of O2 onto pure and doped Al(111) surfaces. Adsorption of O2 was studied at the perfect Al(111) surface and compared with the case where an additional Al atom was present as an adatom. Additionally, we studied how these functionals perform when different dopants are present at the Al(111) surface in two distinct geometries: as an adatom or as a substitutional atom replacing an Al atom. The performance of the different functionals is greatly affected by the surface geometry. The inclusion of Hartree-Fock exchange in the functional leads to slight differences in adsorption energies for molecular adsorption of O2 . These differences become very pronounced for dissociative adsorption, with the hybrids PBE0 and M06 predicting more exergonic adsorption than PBE and M06-L. Furthermore, PBE0 and M06 predicted trends in adsorption energies for defective and perfect surfaces which are in line with the experimental knowledge of the effects of surface defects in adsorption energies. The predictions of the non-hybrids PBE and M06-L point in the opposite direction. The analysis of the contributions of the van der Waals (vdW) forces to the adsorption energies reveals that the PBE and PBE0 functionals have similar difficulties in describing vdW interactions for molecular adsorption of O2 while the M06 functional can give a description of these forces with an accuracy which is at least similar to that of the correction of the D3 type. © 2015 Wiley Periodicals, Inc.

Deterministic growth of AgTCNQ and CuTCNQ nanowires on large-area reduced graphene oxide films for flexible optoelectronics.

PubMed

Zhang, Shuai; Lu, Zhufeng; Gu, Li; Cai, Liling; Cao, Xuebo

2013-11-22

We describe a synchronous reduction and assembly procedure to directly produce large-area reduced graphene oxide (rGO) films sandwiched by a high density of metal nanoparticles (silver and copper). Further, by using the sandwiched metal NPs as sources, networks consisting of AgTCNQ and CuTCNQ nanowires were deterministically grown from the rGO films, forming structurally and functionally integrated rGO/metal-TCNQ hybrid films with outstanding flexibility, bending endurance, and electrical stability. Interestingly, due to the p-type nature of the rGO film and the n-type nature of the metal-TCNQ NWs, the hybrid films are essentially thin-film p-n junctions which are useful in ubiquitous electronics and optoelectronics. Measurements of the optoelectronic properties demonstrate that the rGO/metal-TCNQ hybrid films exhibit substantial photoconductivity and highly reproducible photoswitching behaviours. The present approach may open the door to the versatile and deterministic integration of functional nanostructures into flexible conducting substrates and provide an important step towards producing low-cost and high-performance soft electronic and optoelectronic devices.

QM/MM hybrid calculation of biological macromolecules using a new interface program connecting QM and MM engines

NASA Astrophysics Data System (ADS)

Hagiwara, Yohsuke; Ohta, Takehiro; Tateno, Masaru

2009-02-01

An interface program connecting a quantum mechanics (QM) calculation engine, GAMESS, and a molecular mechanics (MM) calculation engine, AMBER, has been developed for QM/MM hybrid calculations. A protein-DNA complex is used as a test system to investigate the following two types of QM/MM schemes. In a 'subtractive' scheme, electrostatic interactions between QM/MM regions are truncated in QM calculations; in an 'additive' scheme, long-range electrostatic interactions within a cut-off distance from QM regions are introduced into one-electron integration terms of a QM Hamiltonian. In these calculations, 338 atoms are assigned as QM atoms using Hartree-Fock (HF)/density functional theory (DFT) hybrid all-electron calculations. By comparing the results of the additive and subtractive schemes, it is found that electronic structures are perturbed significantly by the introduction of MM partial charges surrounding QM regions, suggesting that biological processes occurring in functional sites are modulated by the surrounding structures. This also indicates that the effects of long-range electrostatic interactions involved in the QM Hamiltonian are crucial for accurate descriptions of electronic structures of biological macromolecules.

Role of Water in the Reversible Optoelectronic Degradation in Hybrid Perovskites at Low Pressure

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

Hall, Genevieve N.; Stuckelberger, Michael; Nietzold, Tara

There is no doubt about the potential offered by the low-cost fabrication and high efficiency of hybrid organic–inorganic perovskite solar cells. However, the service lifetimes of these devices must be increased from months to years to capitalize on their potential. The archetypal hybrid perovskite for solar cells, methylammonium lead iodide (CH 3NH 3PbI 3, abbreviated MAPI), readily degrades in ambient atmosphere under standard operating conditions. Understanding the origin and effects of this degradation can pave the way to better engineer photovoltaic devices and the perovskite material itself. Herein we present the effects of varying pressure on the electrical performance ofmore » MAPI solar cells. Solar cell parameters, especially open circuit voltage, are significantly affected by the total ambient pressure and present an unexpected reversible behavior upon pressure cycling. We complement photoluminescence studies as a function of ambient atmosphere and temperature with first-principles density functional theory (DFT) calculations. The results suggest that the reversible intercalation of water in MAPI is a necessary component underlying this behavior.« less

Dual-functional Pt-on-Pd supported on reduced graphene oxide hybrids: peroxidase-mimic activity and an enhanced electrocatalytic oxidation characteristic.

PubMed

Zhang, Xiahong; Wu, Genghuang; Cai, Zhixiong; Chen, Xi

2015-03-01

In this study, a facile hydrothermal method was developed to synthesize Pt-on-Pd supported on reduced graphene oxide (Pt-on-Pd/RGO) hybrids. Because of the synergistic effect between Pt-on-Pd and RGO, the obtained Pt-on-Pd/RGO had superior peroxidase-mimic activities in H2O2 reduction and TMB oxidation. The reaction medium was optimized and a sensing approach for H2O2 was developed with a linear range from 0.98 to 130.7 μM of H2O2. In addition, the characteristic of electrocatalytic oxidation of methanol was investigated. The peak current density value, j(f), for the Pt-on-Pd/RGO hybrid (328 mA mg(Pt)(-1)) was about 1.85 fold higher than that of commercial Pt black (177 mA mg(Pt)(-1)) and, also, more durable electrocatalytic activity could be obtained. For the first time, the dual-functional Pt-on-Pd/RGO with peroxidase-mimic activity and an enhanced electrocatalytic oxidation characteristic was reported. Copyright © 2014 Elsevier B.V. All rights reserved.

Nature of the insulating ground state of the 5d postperovskite CaIrO 3

DOE PAGES

Kim, Sun -Woo; Liu, Chen; Kim, Hyun -Jung; ...

2015-08-26

In this study, the insulating ground state of the 5d transition metal oxide CaIrO 3 has been classified as a Mott-type insulator. Based on a systematic density functional theory (DFT) study with local, semilocal, and hybrid exchange-correlation functionals, we reveal that the Ir t 2g states exhibit large splittings and one-dimensional electronic states along the c axis due to a tetragonal crystal field. Our hybrid DFT calculation adequately describes the antiferromagnetic (AFM) order along the c direction via a superexchange interaction between Ir 4+ spins. Furthermore, the spin-orbit coupling (SOC) hybridizes the t 2g states to open an insulating gap.more » These results indicate that CaIrO 3 can be represented as a spin-orbit Slater insulator, driven by the interplay between a long-range AFM order and the SOC. Such a Slater mechanism for the gap formation is also demonstrated by the DFT + dynamical mean field theory calculation, where the metal-insulator transition and the paramagnetic to AFM phase transition are concomitant with each other.« less

Role of Water in the Reversible Optoelectronic Degradation in Hybrid Perovskites at Low Pressure

DOE PAGES

Hall, Genevieve N.; Stuckelberger, Michael; Nietzold, Tara; ...

2017-10-10

There is no doubt about the potential offered by the low-cost fabrication and high efficiency of hybrid organic–inorganic perovskite solar cells. However, the service lifetimes of these devices must be increased from months to years to capitalize on their potential. The archetypal hybrid perovskite for solar cells, methylammonium lead iodide (CH 3NH 3PbI 3, abbreviated MAPI), readily degrades in ambient atmosphere under standard operating conditions. Understanding the origin and effects of this degradation can pave the way to better engineer photovoltaic devices and the perovskite material itself. Herein we present the effects of varying pressure on the electrical performance ofmore » MAPI solar cells. Solar cell parameters, especially open circuit voltage, are significantly affected by the total ambient pressure and present an unexpected reversible behavior upon pressure cycling. We complement photoluminescence studies as a function of ambient atmosphere and temperature with first-principles density functional theory (DFT) calculations. The results suggest that the reversible intercalation of water in MAPI is a necessary component underlying this behavior.« less

Two Regimes of Bandgap Red Shift and Partial Ambient Retention in Pressure-Treated Two-Dimensional Perovskites

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

Liu, Gang; Kong, Lingping; Guo, Peijun

The discovery of elevated environmental stability in two-dimensional (2D) Ruddlesden–Popper hybrid perovskites represents a significant advance in low-cost, high-efficiency light absorbers. In comparison to 3D counterparts, 2D perovskites of organo-lead-halides exhibit wider, quantum-confined optical bandgaps that reduce the wavelength range of light absorption. Here, we characterize the structural and optical properties of 2D hybrid perovskites as a function of hydrostatic pressure. We observe bandgap narrowing with pressure of 633 meV that is partially retained following pressure release due to an atomic reconfiguration mechanism. We identify two distinct regimes of compression dominated by the softer organic and less compressible inorganic sublattices.more » Our findings, which also include PL enhancement, correlate well with density functional theory calculations and establish structure–property relationships at the atomic scale. These concepts can be expanded into other hybrid perovskites and suggest that pressure/strain processing could offer a new route to improved materials-by-design in applications.« less

Flexible and freestanding supercapacitor based on nanostructured poly(m-aminophenol)/carbon nanofiber hybrid mats with high energy and power densities

NASA Astrophysics Data System (ADS)

Choudhury, Arup; Dey, Baban; Sinha Mahapatra, Susanta; Kim, Doo-Won; Yang, Kap-Seung; Yang, Duck-Joo

2018-04-01

Nanostructured poly(m-aminophenol) (PmAP) coated freestanding carbon nanofiber (CNF) mats were fabricated through simple in situ rapid-mixing polymerization of m-aminophenol in the presence of a CNF mat for flexible solid-state supercapacitors. The surface compositions, morphology and pore structure of the hybrid mats were characterized by using various techniques, e.g., FTIR, Raman, XRD, FE-SEM, TEM, and N2 absorption. The results show that the PmAP nanoparticles were homogeneously deposited on CNF surfaces and formed a thin flexible hybrid mat, which were directly used to made electrodes for electrochemical analysis without using any binders or conductive additives. The electrochemical performances of the hybrid mats were easily tailored by varying the PmAP loading on a hybrid electrode. The PmAP/CNF-10 hybrid electrode with a relatively low PmAP loading (> 42 wt%) showed a high specific capacitance of 325.8 F g-1 and a volumetric capacitance of 273.6 F cm-3 at a current density of 0.5 A g-1, together with a specific capacitance retention of 196.2 F g-1 at 20 A g-1. The PmAP/CNF-10 hybrid electrode showed good cycling stability with 88.2% capacitance retention after 5000 cycles. A maximum energy density of 45.2 Wh kg-1 and power density of 20.4 kW kg-1 were achieved for the PmAP/CNF-10 hybrid electrode. This facile and cost-effective synthesis of a flexible binder-free PmAP/CNF hybrid mat with excellent capacitive performances encourages its possible commercial exploitation.

Improving the energy density of hydraulic hybrid vehicles (HHVS) and evaluating plug-in HHVS.

DOT National Transportation Integrated Search

2010-10-01

This report describes analyses performed by researchers at The University of Toledo (UT) in : collaboration with researchers at the University of Detroit Mercy (UDM) on the project : Improving the Energy Density of Hydraulic Hybrid Vehicles (HHVs)...

First principles study on the electronic structures and transport properties of armchair/zigzag edge hybridized graphene nanoribbons

NASA Astrophysics Data System (ADS)

Yi, Xiuying; Long, Mengqiu; Liu, Anhua; Li, Mingjun; Xu, Hui

2018-05-01

Graphene nanoribbons (GNRs) can be mainly classified into armchair graphene nanoribbons (aGNRs) and zigzag graphene nanoribbons (zGNRs) by different edge chiral directions. In this work, by introducing Stone-Wales defects on the edges of the V-shaped aGNRs, we propose a kind of armchair/zigzag edge hybridized GNRs (a/zHGNRs) and using the density functional theory and the nonequilibrium Green's function method, the band structures and electronic transport properties of the a/zHGNRs have been calculated. Our results show that an indirect bandgap appears in the band structures of the a/zHGNRs, which is very different from the direct bandgap of aGNRs and gapless of zGNRs. We also find that the valance band is mainly derived from the armchair partial atoms on the hybridized edge, while the conduction band comes mainly from the zigzag partial atoms of the hybridized edge. Meanwhile, the bandgap also oscillates with a period of three when the ribbon width increases. In addition, our quantum transport calculations show that there is a remarkable transition between the semiconductor and the metal with different ribbon widths in the a/zHGNRs devices, and the corresponding physical analysis is given.

Hybrid optimization and Bayesian inference techniques for a non-smooth radiation detection problem

DOE PAGES

Stefanescu, Razvan; Schmidt, Kathleen; Hite, Jason; ...

2016-12-12

In this paper, we propose several algorithms to recover the location and intensity of a radiation source located in a simulated 250 × 180 m block of an urban center based on synthetic measurements. Radioactive decay and detection are Poisson random processes, so we employ likelihood functions based on this distribution. Owing to the domain geometry and the proposed response model, the negative logarithm of the likelihood is only piecewise continuous differentiable, and it has multiple local minima. To address these difficulties, we investigate three hybrid algorithms composed of mixed optimization techniques. For global optimization, we consider simulated annealing, particlemore » swarm, and genetic algorithm, which rely solely on objective function evaluations; that is, they do not evaluate the gradient in the objective function. By employing early stopping criteria for the global optimization methods, a pseudo-optimum point is obtained. This is subsequently utilized as the initial value by the deterministic implicit filtering method, which is able to find local extrema in non-smooth functions, to finish the search in a narrow domain. These new hybrid techniques, combining global optimization and implicit filtering address, difficulties associated with the non-smooth response, and their performances, are shown to significantly decrease the computational time over the global optimization methods. To quantify uncertainties associated with the source location and intensity, we employ the delayed rejection adaptive Metropolis and DiffeRential Evolution Adaptive Metropolis algorithms. Finally, marginal densities of the source properties are obtained, and the means of the chains compare accurately with the estimates produced by the hybrid algorithms.« less

Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization.

PubMed

Sándor, Mónika; Nistor, Cristina Lavinia; Szalontai, Gábor; Stoica, Rusandica; Nicolae, Cristian Andi; Alexandrescu, Elvira; Fazakas, József; Oancea, Florin; Donescu, Dan

2016-01-08

A series of aminopropyl-functionalized silica nanoparticles were prepared through a basic two step sol-gel process in water. Prior to being aminopropyl-functionalized, silica particles with an average diameter of 549 nm were prepared from tetraethyl orthosilicate (TEOS), using a Stöber method. In a second step, aminopropyl-silica particles were prepared by silanization with 3-aminopropyltriethoxysilane (APTES), added drop by drop to the sol-gel mixture. The synthesized amino-functionalized silica particles are intended to be used as supports for immobilization of humic acids (HA), through electrostatic bonds. Furthermore, by inserting beside APTES, unhydrolysable mono-, di- or trifunctional alkylsilanes (methyltriethoxy silane (MeTES), trimethylethoxysilane (Me₃ES), diethoxydimethylsilane (Me₂DES) and 1,2-bis(triethoxysilyl)ethane (BETES)) onto silica particles surface, the spacing of the free amino groups was intended in order to facilitate their interaction with HA large molecules. Two sorts of HA were used for evaluating the immobilization capacity of the novel aminosilane supports. The results proved the efficient functionalization of silica nanoparticles with amino groups and showed that the immobilization of the two tested types of humic acid substances was well achieved for all the TEOS/APTES = 20/1 (molar ratio) silica hybrids having or not having the amino functions spaced by alkyl groups. It was shown that the density of aminopropyl functions is low enough at this low APTES fraction and do not require a further spacing by alkyl groups. Moreover, all the hybrids having negative zeta potential values exhibited low interaction with HA molecules.

Atomic Layer Deposition on Carbon Nanotubes and their Assemblies

NASA Astrophysics Data System (ADS)

Stano, Kelly Lynn

Global issues related to energy and the environment have motivated development of advanced material solutions outside of traditional metals ceramics, and polymers. Taking inspiration from composites, where the combination of two or more materials often yields superior properties, the field of organic-inorganic hybrids has recently emerged. Carbon nanotube (CNT)-inorganic hybrids have drawn widespread and increasing interest in recent years due to their multifunctionality and potential impact across several technologically important application areas. Before the impacts of CNT-inorganic hybrids can be realized however, processing techniques must be developed for their scalable production. Optimization in chemical vapor deposition (CVD) methods for synthesis of CNTs and vertically aligned CNT arrays has created production routes both high throughput and economically feasible. Additionally, control of CVD parameters has allowed for growth of CNT arrays that are able to be drawn into aligned sheets and further processed to form a variety of aligned 1, 2, and 3-dimensional bulk assemblies including ribbons, yarns, and foams. To date, there have only been a few studies on utilizing these bulk assemblies for the production of CNT-inorganic hybrids. Wet chemical methods traditionally used for fabricating CNT-inorganic hybrids are largely incompatible with CNT assemblies, since wetting and drying the delicate structures with solvents can destroy their structure. It is therefore necessary to investigate alternative processing strategies in order to advance the field of CNT-inorganic hybrids. In this dissertation, atomic layer deposition (ALD) is evaluated as a synthetic route for the production of large-scale CNT-metal oxide hybrids as well as pure metal oxide architectures utilizing CNT arrays, ribbons, and ultralow density foams as deposition templates. Nucleation and growth behavior of alumina was evaluated as a function of CNT surface chemistry. While highly graphitic and defect-free CNTs were shown to produce alumina beads on their surfaces, plasma-treated CNTs with a high concentration of oxygen- containing functional groups on their surface promoted conformal film formation. Furthermore, it was determined that ultrahigh aspect ratio CNT assemblies could be uniformly coated throughout the cross-section by orienting the CNT axes parallel to the direction of precursor flow, as well as by removing any barriers to the pump/purge process such as growth substrates or non-porous sample holders. Heat treatment of CNT-alumina hybrids in air not only led to the crystallization of alumina, but also oxidative removal of CNTs from the core-shell structure. In the case of CNT arrays, this resulted in a weak array of alumina nanotubes. When the same process was applied to alumina-coated CNT foams (CNTFs) however, a robust and resilient aerogel-like material remained post-calcination. Further inspection of this novel material revealed that the foam was made up of a three-dimensional network of interconnect alumina nanotubes resulting from the direct templating of alumina on the CNTF structure. With an average density of 1.2 mg cm-3, it is an order of magnitude lower than the lowest density alumina aerogel reported to date, and is among the lowest density for any inorganic aerogel reported to date as well. The structure, and therefore, properties of these novel foams could be easily tuned by varying the thickness of the alumina coating. Evaluation of the compressive behavior of all foams revealed that their mechanical properties exceed those of various foams with similar densities. This was found to be a result of efficient load transfer through the structure due to good connectivity among nanotube ligaments. This connectivity also provided unprecedented elastic recoverability following compression, particularly for thin-walled samples with CNTFs still intact. Structural stability to liquid infiltration and drying increased with the number of ALD cycles, as well as thermal insulation ability.

Practical auxiliary basis implementation of Rung 3.5 functionals

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

Janesko, Benjamin G., E-mail: b.janesko@tcu.edu; Scalmani, Giovanni; Frisch, Michael J.

2014-07-21

Approximate exchange-correlation functionals for Kohn-Sham density functional theory often benefit from incorporating exact exchange. Exact exchange is constructed from the noninteracting reference system's nonlocal one-particle density matrix γ(r{sup -vector},r{sup -vector}′). Rung 3.5 functionals attempt to balance the strengths and limitations of exact exchange using a new ingredient, a projection of γ(r{sup -vector},r{sup -vector} ′) onto a semilocal model density matrix γ{sub SL}(ρ(r{sup -vector}),∇ρ(r{sup -vector}),r{sup -vector}−r{sup -vector} ′). γ{sub SL} depends on the electron density ρ(r{sup -vector}) at reference point r{sup -vector}, and is closely related to semilocal model exchange holes. We present a practical implementation of Rung 3.5 functionals, expandingmore » the r{sup -vector}−r{sup -vector} ′ dependence of γ{sub SL} in an auxiliary basis set. Energies and energy derivatives are obtained from 3D numerical integration as in standard semilocal functionals. We also present numerical tests of a range of properties, including molecular thermochemistry and kinetics, geometries and vibrational frequencies, and bandgaps and excitation energies. Rung 3.5 functionals typically provide accuracy intermediate between semilocal and hybrid approximations. Nonlocal potential contributions from γ{sub SL} yield interesting successes and failures for band structures and excitation energies. The results enable and motivate continued exploration of Rung 3.5 functional forms.« less

A Novel High Energy Density Rechargeable Hybrid Sodium-Air Cell with Acidic Electrolyte.

PubMed

Kang, Yao; Su, Fengmei; Zhang, Qingkai; Liang, Feng; Adair, Keegan R; Chen, Kunfeng; Xue, Dongfeng; Hayashi, Katsuro; Cao, Shan Cecilia; Yadegari, Hossein; Sun, Xueliang

2018-06-22

Low cost, high energy density and highly efficient devices for energy storage have long been desired in our society. Herein, a novel high energy density hybrid sodium-air cell was fabricated successfully based on acidic catholytes. Such a hybrid sodium-air cell possess a high theoretical voltage of 3.94 V, capacity of 1121 mAh g-1, and energy density of 4418 Wh kg-1. Firstly, the buffering effect of an acidic solution was demonstrated, which provides relatively long and stable cell discharge behaviours. Secondly, the catholyte of hybrid sodium-air cells were optimized systematically from the solutions of 0.1 M H3PO4 + 0.1 M Na2SO4 to 0.1 M HAc + 0.1 M NaAc, and it was found that the cells with 0.1 M H3PO4 + 0.1 M Na2SO4 displayed maximum power density of 34.9 mW cm-2. The cell with 0.1 M H3PO4 + 0.1 M Na2SO4 displayed higher discharge capacity of 896 mAh g-1. Moreover, the fabricated acidic hybrid sodium-air cells exhibited stable cycling performance in ambient air, and they delivered a low voltage gap around 0.3 V when the current density is 0.13 mA cm-2, leading to a high energy efficiency up to 90%. Therefore, the present study provides new opportunities to develop highly cost-effective energy storage technologies.

Hybrid simulations of solenoidal radio-frequency inductively coupled hydrogen discharges at low pressures

NASA Astrophysics Data System (ADS)

Yang, Wei; Li, Hong; Gao, Fei; Wang, You-Nian

2016-12-01

In this article, we have described a radio-frequency (RF) inductively coupled H2 plasma using a hybrid computational model, incorporating the Maxwell equations and the linear part of the electron Boltzmann equation into global model equations. This report focuses on the effects of RF frequency, gas pressure, and coil current on the spatial profiles of the induced electric field and plasma absorption power density. The plasma parameters, i.e., plasma density, electron temperature, density of negative ion, electronegativity, densities of neutral species, and dissociation degree of H2, as a function of absorption power, are evaluated at different gas pressures. The simulation results show that the utilization efficiency of the RF source characterized by the coupling efficiency of the RF electric field and power to the plasma can be significantly improved at the low RF frequency, gas pressure, and coil current, due to a low plasma density in these cases. The densities of vibrational states of H2 first rapidly increase with increasing absorption power and then tend to saturate. This is because the rapidly increased dissociation degree of H2 with increasing absorption power somewhat suppresses the increase of the vibrational states of H2, thus inhibiting the increase of the H-. The effects of absorption power on the utilization efficiency of the RF source and the production of the vibrational states of H2 should be considered when setting a value of the coil current. To validate the model simulations, the calculated electron density and temperature are compared with experimental measurements, and a reasonable agreement is achieved.

Electronic structure of LiCoO2 thin films: A combined photoemission spectroscopy and density functional theory study

NASA Astrophysics Data System (ADS)

Ensling, David; Thissen, Andreas; Laubach, Stefan; Schmidt, Peter C.; Jaegermann, Wolfram

2010-11-01

The electronic properties of LiCoO2 have been studied by theoretical band-structure calculations (using density functional theory) and experimental methods (photoemission). Synchrotron-induced photoelectron spectroscopy, resonant photoemission spectroscopy (ResPES), and soft x-ray absorption (XAS) have been applied to investigate the electronic structure of both occupied and unoccupied states. High-quality PES spectra were obtained from stoichiometric and highly crystalline LiCoO2 thin films deposited “in situ” by rf magnetron sputtering. An experimental approach of separating oxygen- and cobalt-derived (final) states by ResPES in the valence-band region is presented. The procedure takes advantage of an antiresonant behavior of cobalt-derived states at the 3p-3d excitation threshold. Information about the unoccupied density of states has been obtained by OK XAS. The structure of the CoL absorption edge is compared to semiempirical charge-transfer multiplet calculations. The experimental results are furthermore compared with band-structure calculations considering three different exchange potentials [generalized gradient approximation (GGA), using a nonlocal Hubbard U (GGA+U) and using a hybrid functional (Becke, three-parameter, Lee-Yang-Parr [B3LYP])]. For these different approaches total density of states and partial valence-band density of states have been investigated. The best qualitative agreement with experimental results has been obtained by using a GGA+U functional with U=2.9eV .

Efficient construction of exchange and correlation potentials by inverting the Kohn-Sham equations.

PubMed

Kananenka, Alexei A; Kohut, Sviataslau V; Gaiduk, Alex P; Ryabinkin, Ilya G; Staroverov, Viktor N

2013-08-21

Given a set of canonical Kohn-Sham orbitals, orbital energies, and an external potential for a many-electron system, one can invert the Kohn-Sham equations in a single step to obtain the corresponding exchange-correlation potential, vXC(r). For orbitals and orbital energies that are solutions of the Kohn-Sham equations with a multiplicative vXC(r) this procedure recovers vXC(r) (in the basis set limit), but for eigenfunctions of a non-multiplicative one-electron operator it produces an orbital-averaged potential. In particular, substitution of Hartree-Fock orbitals and eigenvalues into the Kohn-Sham inversion formula is a fast way to compute the Slater potential. In the same way, we efficiently construct orbital-averaged exchange and correlation potentials for hybrid and kinetic-energy-density-dependent functionals. We also show how the Kohn-Sham inversion approach can be used to compute functional derivatives of explicit density functionals and to approximate functional derivatives of orbital-dependent functionals.

Flag leaf photosynthesis and stomatal function of grain sorghum as influenced by changing photosynthetic photon flux densities

USDA-ARS?s Scientific Manuscript database

Data on physiological parameters of A, gs, Em, Ci, and IWUE in grain sorghum (Sorghum bicolor L. Moench) is limited. Flag leaves from three plants of two hybrids, grown using added N fertilizer rates of 0.0, 112, and 224 kg ha-1 near Elizabeth, MS were field sampled for these parameters at growth s...

Electron affinities and ionization energies of Cu and Ag delafossite compounds: A hybrid functional study

NASA Astrophysics Data System (ADS)

Miao, Mao-Sheng; Yarbro, Sam; Barton, Phillip T.; Seshadri, Ram

2014-01-01

Using density functional theory with a hybrid functional, we calculate the ionization energies and electron affinities of a series of delafossite compounds (AMO2: A =Cu, Ag; M =B, Al, Ga, In, Sc). The alignments of the valence band maximum and the conduction band minimum, which directly relate to the ionization energies and electron affinities, were obtained by calculations of supercell slab models constructed in a nonpolar orientation. Our calculations reveal that the ionization energy decreases with an increasing atomic number of group-III elements, and thus suggest an improved p-type doping propensity for heavier compounds. For keeping both a low ionization energy and a band gap of sufficient size, CuScO2 is superior to the Cu-based group-III delafossites. By analyzing the electronic structures, we demonstrate that the compositional trend of the ionization energies and electron affinities is the result of a combined effect of d-band broadening due to Cu(Ag)-Cu(Ag) coupling and a repositioning of the d-band center.

Hybrid multiphoton volumetric functional imaging of large-scale bioengineered neuronal networks

NASA Astrophysics Data System (ADS)

Dana, Hod; Marom, Anat; Paluch, Shir; Dvorkin, Roman; Brosh, Inbar; Shoham, Shy

2014-06-01

Planar neural networks and interfaces serve as versatile in vitro models of central nervous system physiology, but adaptations of related methods to three dimensions (3D) have met with limited success. Here, we demonstrate for the first time volumetric functional imaging in a bioengineered neural tissue growing in a transparent hydrogel with cortical cellular and synaptic densities, by introducing complementary new developments in nonlinear microscopy and neural tissue engineering. Our system uses a novel hybrid multiphoton microscope design combining a 3D scanning-line temporal-focusing subsystem and a conventional laser-scanning multiphoton microscope to provide functional and structural volumetric imaging capabilities: dense microscopic 3D sampling at tens of volumes per second of structures with mm-scale dimensions containing a network of over 1,000 developing cells with complex spontaneous activity patterns. These developments open new opportunities for large-scale neuronal interfacing and for applications of 3D engineered networks ranging from basic neuroscience to the screening of neuroactive substances.

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.

Hybrid rocket propulsion

NASA Technical Reports Server (NTRS)

Holzman, Allen L.

1993-01-01

Topics addressed are: (1) comparison of the theoretical impulses; (2) comparison of the density-specific impulses; (3) general propulsion system features comparison; (4) hybrid systems, booster applications; and (5) hybrid systems, upper stage propulsion applications.

The hybrid nanostructure of MnCo2O4.5 nanoneedle/carbon aerogel for symmetric supercapacitors with high energy density.

PubMed

Hao, Pin; Zhao, Zhenhuan; Li, Liyi; Tuan, Chia-Chi; Li, Haidong; Sang, Yuanhua; Jiang, Huaidong; Wong, C P; Liu, Hong

2015-09-14

Current applications of carbon-based supercapacitors are limited by their low energy density. One promising strategy to enhance the energy density is to couple metal oxides with carbon materials. In this study, a porous MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure was synthesized by assembling MnCo2O4.5 nanoneedle arrays on the surface of channel walls of hierarchical porous carbon aerogels derived from chitosan for the supercapacitor application. The synthetic process of the hybrid nanostructure involves two steps, i.e. the growth of Mn-Co precursors on carbon aerogel by a hydrothermal process and the conversion of the precursor into MnCo2O4.5 nanoneedles by calcination. The carbon aerogel exhibits a high electrical conductivity, high specific surface area and porous structure, ensuring high electrochemical performance of the hybrid nanostructure when coupled with the porous MnCo2O4.5 nanoneedles. The symmetric supercapacitor using the MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure as the active electrode material exhibits a high energy density of about 84.3 Wh kg(-1) at a power density of 600 W kg(-1). The voltage window is as high as 1.5 V in neutral aqueous electrolytes. Due to the unique nanostructure of the electrodes, the capacitance retention reaches 86% over 5000 cycles.

Magnetic behavior of Si-Ge bond in SixGe4-x nano-clusters

NASA Astrophysics Data System (ADS)

Nahali, Masoud; Mehri, Ali

2018-06-01

The structure of SixGe4-x nano-clusters were optimized by MPW1B95 level of theory using MG3S and SDB-aug-cc-PVTZ basis set. The agreement of the calculated ionization and dissociation energies with experimental values validates the reported structures of nano-clusters and justifies the use of hybrid meta density functional method. Since the Si-Si bond is stronger than Si-Ge and Ge-Ge bonds, the Si-Si, Si-Ge, and Ge-Ge diagonal bonds determine the precedence of the stability in these nano-clusters. The hybrid meta density functional calculations were carried out to investigate the adsorption of CO on all possible SixGe4-x nano-clusters. It was found that the silicon atom generally makes a stronger bond with CO than germanium and thereby preferentially affects the shape of structures having higher multiplicity. In Si-Ge structures with higher spin more than 95% of spins accumulate on positions with less bonds to other atoms of the cluster. Through CO adsorption on these clusters bridge structures are made that behave as spin bridge which conduct the spin from the nano-cluster surface to the adsorbate atoms. A better understanding of bridged structures was achieved upon introducing the 'spin bridge' concept. Based on exhaustive spin density analysis, it was found that the reason for the extra negative charge on oxygen in the bridged structures is the relocation of spin from the surface through the bridge.

A first principles study of the mechanical, electronic, and vibrational properties of lead oxide

NASA Astrophysics Data System (ADS)

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

2017-11-01

The first principles study of the crystal structure, chemical bonds, elastic and mechanical properties, electron energy band structure and density, and normal long-wave vibrations of nine phases of lead monoxide, dioxide, and tetraoxide has been performed under normal and external pressure within the framework of density functional theory (DFT) with the Perdew-Becke-Ernzerhof (PBE) gradient exchange-correlation functional and its hybrid version with a 25-% Hartree-Fock (HF) exchange contribution in the basis of localized atom orbitals. The behavior of physical parameters has been studied using the cold four- and threeparameter equations of state. The parameters of the crystal structures are in satisfactory agreement with experimental data, and elastic constants indicate their mechanical stability and anisotropy in the elastic properties. The elasticity, shear, and Young moduli, hardness, acoustic velocities, and Debye temperature of dioxide on the one hand and monoxide and tetraoxide on the other hand appreciably differ from each other. The difference between electron properties may be explained by the character of hybridization in the upper filled and lower empty energy bands as evident from the density of states. In monoxide, the indirect band gap width decreases with increasing pressure at a rate of 0.16 eV/GPa, and the direct band gap width increases at a rate of 0.13 eV/GPa. To identify crystalline phases, the frequencies and intensities of long-wave modes active in IR and Raman spectra have been calculated.

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.

Electronic and optical response of zirconium sulphoselenides: Compton spectroscopy and first-principles calculations

NASA Astrophysics Data System (ADS)

Kumar, Kishor; Bhatt, Samir; Jani, A. R.; Ahuja, B. L.

2015-12-01

We present the first-ever experimental Compton profiles (CPs) of ZrSSe2 and ZrS1.5Se1.5 using 100 mCi 241Am Compton spectrometer. To analyze the experimental momentum densities, we have computed for the first-time the CPs, energy bands and density of states using linear combination of atomic orbitals (LCAO) method. To model the exchange and correlation effects within LCAO approach, we have considered Hartree-Fock (HF), density functional theory (DFT) with revised functional of Perdew-Becke-Ernzerhof (PBEsol) and hybridization of HF and DFT. Going beyond computation of electronic properties using LCAO method, we have also derived electronic and optical properties using the modified Becke-Johnson (mBJ) potential within full potential linearized augmented plane wave (FP-LAPW) method. There is notable decrease in the energy band gap on replacing S by Se atoms in ZrSSe2 to obtain ZrS1.5Se1.5 composition, which is mainly attributed to readjustment of Zr-4d, S-3p and Se-4p states. It is seen that the CPs based on hybridization of HF and DFT show a better agreement with the experimental profiles than those based on individual HF and DFT-GGA-PBEsol schemes. The optical properties computed using FP-LAPW-mBJ method unambiguously depict feasibility of using both the sulphoselenides in photovoltaics and also utility of ZrS1.5Se1.5 in the field of non-linear optics.

Control algorithms for aerobraking in the Martian atmosphere

NASA Technical Reports Server (NTRS)

Ward, Donald T.; Shipley, Buford W., Jr.

1991-01-01

The Analytic Predictor Corrector (APC) and Energy Controller (EC) atmospheric guidance concepts were adapted to control an interplanetary vehicle aerobraking in the Martian atmosphere. Changes are made to the APC to improve its robustness to density variations. These changes include adaptation of a new exit phase algorithm, an adaptive transition velocity to initiate the exit phase, refinement of the reference dynamic pressure calculation and two improved density estimation techniques. The modified controller with the hybrid density estimation technique is called the Mars Hybrid Predictor Corrector (MHPC), while the modified controller with a polynomial density estimator is called the Mars Predictor Corrector (MPC). A Lyapunov Steepest Descent Controller (LSDC) is adapted to control the vehicle. The LSDC lacked robustness, so a Lyapunov tracking exit phase algorithm is developed to guide the vehicle along a reference trajectory. This algorithm, when using the hybrid density estimation technique to define the reference path, is called the Lyapunov Hybrid Tracking Controller (LHTC). With the polynomial density estimator used to define the reference trajectory, the algorithm is called the Lyapunov Tracking Controller (LTC). These four new controllers are tested using a six degree of freedom computer simulation to evaluate their robustness. The MHPC, MPC, LHTC, and LTC show dramatic improvements in robustness over the APC and EC.

The hybrid nanostructure of MnCo2O4.5 nanoneedle/carbon aerogel for symmetric supercapacitors with high energy density

NASA Astrophysics Data System (ADS)

Hao, Pin; Zhao, Zhenhuan; Li, Liyi; Tuan, Chia-Chi; Li, Haidong; Sang, Yuanhua; Jiang, Huaidong; Wong, C. P.; Liu, Hong

2015-08-01

Current applications of carbon-based supercapacitors are limited by their low energy density. One promising strategy to enhance the energy density is to couple metal oxides with carbon materials. In this study, a porous MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure was synthesized by assembling MnCo2O4.5 nanoneedle arrays on the surface of channel walls of hierarchical porous carbon aerogels derived from chitosan for the supercapacitor application. The synthetic process of the hybrid nanostructure involves two steps, i.e. the growth of Mn-Co precursors on carbon aerogel by a hydrothermal process and the conversion of the precursor into MnCo2O4.5 nanoneedles by calcination. The carbon aerogel exhibits a high electrical conductivity, high specific surface area and porous structure, ensuring high electrochemical performance of the hybrid nanostructure when coupled with the porous MnCo2O4.5 nanoneedles. The symmetric supercapacitor using the MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure as the active electrode material exhibits a high energy density of about 84.3 Wh kg-1 at a power density of 600 W kg-1. The voltage window is as high as 1.5 V in neutral aqueous electrolytes. Due to the unique nanostructure of the electrodes, the capacitance retention reaches 86% over 5000 cycles.Current applications of carbon-based supercapacitors are limited by their low energy density. One promising strategy to enhance the energy density is to couple metal oxides with carbon materials. In this study, a porous MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure was synthesized by assembling MnCo2O4.5 nanoneedle arrays on the surface of channel walls of hierarchical porous carbon aerogels derived from chitosan for the supercapacitor application. The synthetic process of the hybrid nanostructure involves two steps, i.e. the growth of Mn-Co precursors on carbon aerogel by a hydrothermal process and the conversion of the precursor into MnCo2O4.5 nanoneedles by calcination. The carbon aerogel exhibits a high electrical conductivity, high specific surface area and porous structure, ensuring high electrochemical performance of the hybrid nanostructure when coupled with the porous MnCo2O4.5 nanoneedles. The symmetric supercapacitor using the MnCo2O4.5 nanoneedle/carbon aerogel hybrid nanostructure as the active electrode material exhibits a high energy density of about 84.3 Wh kg-1 at a power density of 600 W kg-1. The voltage window is as high as 1.5 V in neutral aqueous electrolytes. Due to the unique nanostructure of the electrodes, the capacitance retention reaches 86% over 5000 cycles. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04421a

Surface supported gold-organic hybrids: on-surface synthesis and surface directed orientation.

PubMed

Zhang, Haiming; Franke, Jörn-Holger; Zhong, Dingyong; Li, Yan; Timmer, Alexander; Arado, Oscar Díaz; Mönig, Harry; Wang, Hong; Chi, Lifeng; Wang, Zhaohui; Müllen, Klaus; Fuchs, Harald

2014-04-09

The surface-assisted synthesis of gold-organic hybrids on Au (111) and Au (100) surfaces is repotred by thermally initiated dehalogenation of chloro-substituted perylene-3,4,9,10-tetracarboxylic acid bisimides (PBIs). Structures and surface-directed alignment of the Au-PBI chains are investigated by scanning tunnelling microscopy in ultra high vacuum conditions. Using dichloro-PBI as a model system, the mechanism for the formation of Au-PBI dimer is revealed with scanning tunnelling microscopy studies and density functional theory calculations. A PBI radical generated from the homolytic C-Cl bond dissociation can covalently bind a surface gold atom and partially pull it out of the surface to form stable PBI-Au hybrid species, which also gives rise to the surface-directed alignment of the Au-PBI chains on reconstructed Au (100) surfaces. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polymer-metal hybrid transparent electrodes for flexible electronics

NASA Astrophysics Data System (ADS)

Kang, Hongkyu; Jung, Suhyun; Jeong, Soyeong; Kim, Geunjin; Lee, Kwanghee

2015-03-01

Despite nearly two decades of research, the absence of ideal flexible and transparent electrodes has been the largest obstacle in realizing flexible and printable electronics for future technologies. Here we report the fabrication of ‘polymer-metal hybrid electrodes’ with high-performance properties, including a bending radius <1 mm, a visible-range transmittance>95% and a sheet resistance <10 Ω sq-1. These features arise from a surface modification of the plastic substrates using an amine-containing nonconjugated polyelectrolyte, which provides ideal metal-nucleation sites with a surface-density on the atomic scale, in combination with the successive deposition of a facile anti-reflective coating using a conducting polymer. The hybrid electrodes are fully functional as universal electrodes for high-end flexible electronic applications, such as polymer solar cells that exhibit a high power conversion efficiency of 10% and polymer light-emitting diodes that can outperform those based on transparent conducting oxides.

Polymer-metal hybrid transparent electrodes for flexible electronics

PubMed Central

Kang, Hongkyu; Jung, Suhyun; Jeong, Soyeong; Kim, Geunjin; Lee, Kwanghee

2015-01-01

Despite nearly two decades of research, the absence of ideal flexible and transparent electrodes has been the largest obstacle in realizing flexible and printable electronics for future technologies. Here we report the fabrication of ‘polymer-metal hybrid electrodes’ with high-performance properties, including a bending radius <1 mm, a visible-range transmittance>95% and a sheet resistance <10 Ω sq−1. These features arise from a surface modification of the plastic substrates using an amine-containing nonconjugated polyelectrolyte, which provides ideal metal-nucleation sites with a surface-density on the atomic scale, in combination with the successive deposition of a facile anti-reflective coating using a conducting polymer. The hybrid electrodes are fully functional as universal electrodes for high-end flexible electronic applications, such as polymer solar cells that exhibit a high power conversion efficiency of 10% and polymer light-emitting diodes that can outperform those based on transparent conducting oxides. PMID:25790133

Graphene-induced band gap renormalization in polythiophene: a many-body perturbation study

NASA Astrophysics Data System (ADS)

Marsusi, F.; Fedorov, I. A.; Gerivani, S.

2018-01-01

Density functional theory and many-body perturbation theory at the G0W0 level are employed to study the electronic properties of polythiophene (PT) adsorbed on the graphene surface. Analysis of the charge density difference shows that substrate-adsorbate interaction leads to a strong physisorption and interfacial electric dipole moment formation. The electrostatic potential displays a  -0.19 eV shift in the graphene work function from its initial value of 4.53 eV, as the result of the interaction. The LDA band gap of the polymer does not show any change. However, the band structure exhibits weak orbital hybridizations resulting from slight overlapping between the polymer and graphene states wave functions. The interfacial polarization effects on the band gap and levels alignment are investigated at the G0W0 level and show a notable reduction of PT band gap compared to that of the isolated chain.

Application of double-hybrid density functionals to charge transfer in N-substituted pentacenequinones.

PubMed

Sancho-García, J C

2012-05-07

A set of N-heteroquinones, deriving from oligoacenes, have been recently proposed as n-type organic semiconductors with high electron mobilities in thin-film transistors. Generally speaking, this class of compounds self-assembles in neighboring π-stacks linked by weak hydrogen bonds. We aim at theoretically characterizing here the sequential charge transport (hopping) process expected to take place across these arrays of molecules. To do so, we need to accurately address the preferred packing of these materials simultaneously to single-molecule properties related to charge-transfer events, carefully employing dispersion-corrected density functional theory methods to accurately extract the key molecular parameters governing this phenomenon at the nanoscale. This study confirms the great deal of interest around these compounds, since controlled functionalization of model molecules (i.e., pentacene) allows to efficiently tune the corresponding charge mobilities, and the capacity of modern quantum-chemical methods to predict it after rationalizing the underlying structure-property relationships.

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

Tokár, K.; Derian, R.; Mitas, L.

Using explicitly correlated fixed-node quantum Monte Carlo and density functional theory (DFT) methods, we study electronic properties, ground-state multiplets, ionization potentials, electron affinities, and low-energy fragmentation channels of charged half-sandwich and multidecker vanadium-benzene systems with up to 3 vanadium atoms, including both anions and cations. It is shown that, particularly in anions, electronic correlations play a crucial role; these effects are not systematically captured with any commonly used DFT functionals such as gradient corrected, hybrids, and range-separated hybrids. On the other hand, tightly bound cations can be described qualitatively by DFT. A comparison of DFT and quantum Monte Carlo providesmore » an in-depth understanding of the electronic structure and properties of these correlated systems. The calculations also serve as a benchmark study of 3d molecular anions that require a balanced many-body description of correlations at both short- and long-range distances.« less

Electron binding energy of uranium-ligand and uranyl-ligand anions

NASA Astrophysics Data System (ADS)

Wang, Lei; Horowitz, Steven; Marston, Brad

2012-02-01

Electron binding energies of the early actinide element uranium in gas-phase anion complexes are calculated by relativistic density functional theory (DFT) with two different exchange-correlation functions (RPBE and B3LYP) and also in the Hartree-Fock (HF) approximationootnotetextADF2010.02, SCM.com. Scalar and spin-orbit calculations are performed, and the calculated energies are compared to available experimental measurements and shown to disagree by energies of order 1 eV. Strong correlations that are poorly treated in DFT and HF can be included by a hybrid approach in which a generalized Anderson impurity model is numerically diagonalized. Reduction-oxidation (redox) potentials of aqueous actinide ions show improved agreement with measured values in the hybrid approachootnotetextS. E. Horowitz and J. B. Marston, J. Chem. Phys 134 064510 (2011).. We test whether or not similar improvements are found in the gas-phase.

When Anatase Nanoparticles Become Bulklike: Properties of Realistic TiO2 Nanoparticles in the 1-6 nm Size Range from All Electron Relativistic Density Functional Theory Based Calculations.

PubMed

Lamiel-Garcia, Oriol; Ko, Kyoung Chul; Lee, Jin Yong; Bromley, Stefan T; Illas, Francesc

2017-04-11

All electron relativistic density functional theory (DFT) based calculations using numerical atom-centered orbitals have been carried out to explore the relative stability, atomic, and electronic structure of a series of stoichiometric TiO 2 anatase nanoparticles explicitly containing up to 1365 atoms as a function of size and morphology. The nanoparticles under scrutiny exhibit octahedral or truncated octahedral structures and span the 1-6 nm diameter size range. Initial structures were obtained using the Wulff construction, thus exhibiting the most stable (101) and (001) anatase surfaces. Final structures were obtained from geometry optimization with full relaxation of all structural parameters using both generalized gradient approximation (GGA) and hybrid density functionals. Results show that, for nanoparticles of a similar size, octahedral and truncated octahedral morphologies have comparable energetic stabilities. The electronic structure properties exhibit a clear trend converging to the bulk values as the size of the nanoparticles increases but with a marked influence of the density functional employed. Our results suggest that electronic structure properties, and hence reactivity, for the largest anatase nanoparticles considered in this study will be similar to those exhibited by even larger mesoscale particles or by bulk systems. Finally, we present compelling evidence that anatase nanoparticles become effectively bulklike when reaching a size of ∼20 nm diameter.

Influence of the excitation frequency on the density of helium metastable atoms in an atmospheric pressure dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Boisvert, J.-S.; Sadeghi, N.; Margot, J.; Massines, F.

2017-01-01

Diffuse dielectric barrier discharges in atmospheric-pressure helium can be sustained over a wide range of excitation frequencies (from, but not restricted, 25 kHz to 15 MHz). The aim of the present paper is to identify the specific characteristics of the discharge modes that can be sustained in this frequency range, namely, the atmospheric-pressure Townsend-like discharge (APTD-L) mode, the atmospheric-pressure glow discharge (APGD) mode, the Ω mode, the hybrid mode, and the RF-α mode. This is achieved experimentally, by measuring the density of helium metastable atoms, which are known to play a driving role on the discharge kinetics. This density is measured by means of two absorption spectroscopy methods, one using a spectral lamp and the other one using a diode laser as a light source. The first one provides the time-averaged atom densities in the singlet He(21S) and triplet He(23S) metastable states, while with the second one we access the time-resolved density of He(23S) atoms. Time-averaged measurements indicate that the He(23S) density is relatively low in the APTD-L, the Ω and the RF-α modes ( <4 ×1016 m-3 ) slightly higher in the APGD mode ( 2 -7 ×1016 m-3 ), and still higher ( >1 ×1017 m-3 ) in the hybrid mode. The hybrid mode is exclusively observed for frequencies from 0.2 to 3 MHz. However, time-resolved density measurement shows that at 1 MHz and below, the hybrid mode is not continuously sustained. Instead, the discharge oscillates between the Ω and the hybrid mode with a switching frequency about the kilohertz. This explains the significantly lower power required to sustain the plasma as compared to above 1 MHz.

Theoretical study on third-order nonlinear optical properties in hexagonal graphene nanoflakes: Edge shape effect

NASA Astrophysics Data System (ADS)

Nagai, Hiroshi; Nakano, Masayoshi; Yoneda, Kyohei; Fukui, Hitoshi; Minami, Takuya; Bonness, Sean; Kishi, Ryohei; Takahashi, Hideaki; Kubo, Takashi; Kamada, Kenji; Ohta, Koji; Champagne, Benoît; Botek, Edith

2009-08-01

Using hybrid density functional theory methods, we investigate the second hyperpolarizabilities ( γ) of hexagonal shaped finite graphene fragments, which are referred to as hexagonal graphene nanoflakes (HGNFs), with two types of edge shapes: zigzag (Z) and armchair (A) edges. It is found that Z-HGNF, which gives intermediate diradical characters ( y), exhibits about 3.3 times larger orthogonal components of γ ( γ xxxx = γ yyyy in this case) than A-HGNF, which gives zero y value (closed-shell system). The γ density analysis reveals that this enhancement originates in the significant contribution of γ densities on edge regions in Z-HGNF. These observations strongly indicate that Z-HGNF is a promising candidate of open-shell singlet NLO systems.

The vibrational properties of the bee-killer imidacloprid insecticide: A molecular description

NASA Astrophysics Data System (ADS)

Moreira, Antônio A. G.; De Lima-Neto, Pedro; Caetano, Ewerton W. S.; Barroso-Neto, Ito L.; Freire, Valder N.

2017-10-01

The chemical imidacloprid belongs to the neonicotinoids insecticide class, widely used for insect pest control mainly for crop protection. However, imidacloprid is a non-selective agrochemical to the insects and it is able to kill the most important pollinators, the bees. The high toxicity of imidacloprid requires controlled release and continuous monitoring. For this purpose, high performance liquid chromatography (HPLC) is usually employed; infrared and Raman spectroscopy, however, are simple and viable techniques that can be adapted to portable devices for field application. In this communication, state-of-the-art quantum level simulations were used to predict the infrared and Raman spectra of the most stable conformer of imidacloprid. Four molecular geometries were investigated in vacuum and solvated within the Density Functional Theory (DFT) approach employing the hybrid meta functional M06-2X and the hybrid functional B3LYP. The M062X/PCM model proved to be the best to predict structural features, while the values of harmonic vibrational frequencies were predicted more accurately using the B3LYP functional.

Dissecting the accountability of parameterized and parameter-free single-hybrid and double-hybrid functionals for photophysical properties of TADF-based OLEDs

NASA Astrophysics Data System (ADS)

Alipour, Mojtaba; Karimi, Niloofar

2017-06-01

Organic light emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters are an attractive category of materials that have witnessed a booming development in recent years. In the present contribution, we scrutinize the accountability of parameterized and parameter-free single-hybrid (SH) and double-hybrid (DH) functionals through the two formalisms, full time-dependent density functional theory (TD-DFT) and Tamm-Dancoff approximation (TDA), for the estimation of photophysical properties like absorption energy, emission energy, zero-zero transition energy, and singlet-triplet energy splitting of TADF molecules. According to our detailed analyses on the performance of SHs based on TD-DFT and TDA, the TDA-based parameter-free SH functionals, PBE0 and TPSS0, with one-third of exact-like exchange turned out to be the best performers in comparison to other functionals from various rungs to reproduce the experimental data of the benchmarked set. Such affordable SH approximations can thus be employed to predict and design the TADF molecules with low singlet-triplet energy gaps for OLED applications. From another perspective, considering this point that both the nonlocal exchange and correlation are essential for a more reliable description of large charge-transfer excited states, applicability of the functionals incorporating these terms, namely, parameterized and parameter-free DHs, has also been evaluated. Perusing the role of exact-like exchange, perturbative-like correlation, solvent effects, and other related factors, we find that the parameterized functionals B2π-PLYP and B2GP-PLYP and the parameter-free models PBE-CIDH and PBE-QIDH have respectable performance with respect to others. Lastly, besides the recommendation of reliable computational protocols for the purpose, hopefully this study can pave the way toward further developments of other SHs and DHs for theoretical explorations in the field of OLEDs technology.

Benchmarking DFT and semi-empirical methods for a reliable and cost-efficient computational screening of benzofulvene derivatives as donor materials for small-molecule organic solar cells.

PubMed

Tortorella, Sara; Talamo, Maurizio Mastropasqua; Cardone, Antonio; Pastore, Mariachiara; De Angelis, Filippo

2016-02-24

A systematic computational investigation on the optical properties of a group of novel benzofulvene derivatives (Martinelli 2014 Org. Lett. 16 3424-7), proposed as possible donor materials in small molecule organic photovoltaic (smOPV) devices, is presented. A benchmark evaluation against experimental results on the accuracy of different exchange and correlation functionals and semi-empirical methods in predicting both reliable ground state equilibrium geometries and electronic absorption spectra is carried out. The benchmark of the geometry optimization level indicated that the best agreement with x-ray data is achieved by using the B3LYP functional. Concerning the optical gap prediction, we found that, among the employed functionals, MPW1K provides the most accurate excitation energies over the entire set of benzofulvenes. Similarly reliable results were also obtained for range-separated hybrid functionals (CAM-B3LYP and wB97XD) and for global hybrid methods incorporating a large amount of non-local exchange (M06-2X and M06-HF). Density functional theory (DFT) hybrids with a moderate (about 20-30%) extent of Hartree-Fock exchange (HFexc) (PBE0, B3LYP and M06) were also found to deliver HOMO-LUMO energy gaps which compare well with the experimental absorption maxima, thus representing a valuable alternative for a prompt and predictive estimation of the optical gap. The possibility of using completely semi-empirical approaches (AM1/ZINDO) is also discussed.

Atomic Mechanism of Hybridization-Dependent Surface Reconstruction with Tailored Functionality in Hexagonal Multiferroics.

PubMed

Deng, Shiqing; Cheng, Shaobo; Xu, Changsong; Ge, Binghui; Sun, Xuefeng; Yu, Rong; Duan, Wenhui; Zhu, Jing

2017-08-16

The broken symmetry along with anomalous defect structures and charging conditions at multiferroics surface can alter both crystal structures and electronic configurations, bringing in emergent physical properties. Extraordinary surface states are induced into original mutually coupled order parameters in such strongly correlated oxides, which flourish in diverse properties but remain less explored. Here, we report the peculiar surface ferroelectric states and reconfigurable functionalities driven by the relaxation of surface and consequent changes in O 2p and Y 4d orbital (p-d) hybridization within a representative hexagonal multiferroics, YMnO 3 . An unprecedented surface reconstruction is achieved by tailored p-d hybridization coupling with in-plane oxygen vacancies, which is atomically revealed on the basis of the advantages of state-of-the-art aberration-corrected (scanning) transmission electron microscopy. Further ab initio density functional theory calculations verify the key roles of in-plane oxygen vacancies in modulating polarization properties and electronic structure, which should be regarded as the atomic multiferroic element. This surface configuration is found to induce tunable functionalities, such as surface ferromagnetism and conductivity. Meanwhile, the controversial origin of improper ferroelectricity that is unexpectedly free from critical size has also been atomically unraveled. Our findings provide new insights into the design and implementation of surface chemistry devices by simply controlling the oxygen stoichiometry, greatly advance our understandings of surface science in strongly correlated oxides, and enable exciting innovations and new technological functionality paradigms.

Experimental and DFT studies on the vibrational spectra of 1H-indene-2-boronic acid

NASA Astrophysics Data System (ADS)

Alver, Özgur; Kaya, Mehmet Fatih

2014-11-01

Stable conformers and geometrical molecular structures of 1H-indene-2-boronic acid (I-2B(OH)2) were studied experimentally and theoretically using FT-IR and FT-Raman spectroscopic methods. FT-IR and FT-Raman spectra were recorded in the region of 4000-400 cm-1, and 3700-400 cm-1, respectively. The optimized geometric structures were searched by Becke-3-Lee-Yang-Parr (B3LYP) hybrid density functional theory method with 6-31++G(d,p) basis set. Vibrational wavenumbers of I-2B(OH)2 were calculated using B3LYP density functional methods including 6-31++G(d,p) basis set. Experimental and theoretical results show that density functional B3LYP method gives satisfactory results for predicting vibrational wavenumbers except OH stretching modes which is probably due to increasing unharmonicity in the high wave number region and possible intra and inter molecular interaction at OH edges. To support the assigned vibrational wavenumbers, the potential energy distribution (PED) values were also calculated using VEDA 4 (Vibrational Energy Distribution Analysis) program.

CuPc/Au(1 1 0): Determination of the azimuthal alignment by a combination of angle-resolved photoemission and density functional theory

PubMed Central

Lüftner, Daniel; Milko, Matus; Huppmann, Sophia; Scholz, Markus; Ngyuen, Nam; Wießner, Michael; Schöll, Achim; Reinert, Friedrich; Puschnig, Peter

2014-01-01

Here we report on a combined experimental and theoretical study on the structural and electronic properties of a monolayer of Copper-Phthalocyanine (CuPc) on the Au(1 1 0) surface. Low-energy electron diffraction reveals a commensurate overlayer unit cell containing one adsorbate species. The azimuthal alignment of the CuPc molecule is revealed by comparing experimental constant binding energy (kxky)-maps using angle-resolved photoelectron spectroscopy with theoretical momentum maps of the free molecule's highest occupied molecular orbital (HOMO). This structural information is confirmed by total energy calculations within the framework of van-der-Waals corrected density functional theory. The electronic structure is further analyzed by computing the molecule-projected density of states, using both a semi-local and a hybrid exchange-correlation functional. In agreement with experiment, the HOMO is located about 1.2 eV below the Fermi-level, while there is no significant charge transfer into the molecule and the CuPc LUMO remains unoccupied on the Au(1 1 0) surface. PMID:25284953

Density Functional Calculations of Native Defects in CH 3 NH 3 PbI 3 : Effects of Spin–Orbit Coupling and Self-Interaction Error

DOE PAGES

Du, Mao-Hua

2015-04-02

We know that native point defects play an important role in carrier transport properties of CH3NH3PbI3. However, the nature of many important defects remains controversial due partly to the conflicting results reported by recent density functional theory (DFT) calculations. In this Letter, we show that self-interaction error and the neglect of spin–orbit coupling (SOC) in many previous DFT calculations resulted in incorrect positions of valence and conduction band edges, although their difference, which is the band gap, is in good agreement with the experimental value. Moreover, this problem has led to incorrect predictions of defect-level positions. Hybrid density functional calculations,more » which partially correct the self-interaction error and include the SOC, show that, among native point defects (including vacancies, interstitials, and antisites), only the iodine vacancy and its complexes induce deep electron and hole trapping levels inside of the band gap, acting as nonradiative recombination centers.« less

Nanostructured Na2Ti9O19 for Hybrid Sodium-Ion Capacitors with Excellent Rate Capability.

PubMed

Bhat, Swetha S M; Babu, Binson; Feygenson, Mikhail; Neuefeind, Joerg C; Shaijumon, M M

2018-01-10

Herein, we report a new Na-insertion electrode material, Na 2 Ti 9 O 19 , as a potential candidate for Na-ion hybrid capacitors. We study the structural properties of nanostructured Na 2 Ti 9 O 19 , synthesized by a hydrothermal technique, upon electrochemical cycling vs Na. Average and local structures of Na 2 Ti 9 O 19 are elucidated from neutron Rietveld refinement and pair distribution function (PDF), respectively, to investigate the initial discharge and charge events. Rietveld refinement reveals electrochemical cycling of Na 2 Ti 9 O 19 is driven by single-phase solid solution reaction during (de)sodiation without any major structural deterioration, keeping the average structure intact. Unit cell volume and lattice evolution on discharge process is inherently related to TiO 6 distortion and Na ion perturbations, while the PDF reveals the deviation in the local structure after sodiation. Raman spectroscopy and X-ray photoelectron spectroscopy studies further corroborate the average and local structural behavior derived from neutron diffraction measurements. Also, Na 2 Ti 9 O 19 shows excellent Na-ion kinetics with a capacitve nature of 86% at 1.0 mV s -1 , indicating that the material is a good anode candidate for a sodium-ion hybrid capacitor. A full cell hybrid Na-ion capacitor is fabricated by using Na 2 Ti 9 O 19 as anode and activated porous carbon as cathode, which exhibits excellent electrochemical properties, with a maximum energy density of 54 Wh kg -1 and a maximum power density of 5 kW kg -1 . Both structural insights and electrochemical investigation suggest that Na 2 Ti 9 O 19 is a promising negative electrode for sodium-ion batteries and hybrid capacitors.

A multiply-add engine with monolithically integrated 3D memristor crossbar/CMOS hybrid circuit.

PubMed

Chakrabarti, B; Lastras-Montaño, M A; Adam, G; Prezioso, M; Hoskins, B; Payvand, M; Madhavan, A; Ghofrani, A; Theogarajan, L; Cheng, K-T; Strukov, D B

2017-02-14

Silicon (Si) based complementary metal-oxide semiconductor (CMOS) technology has been the driving force of the information-technology revolution. However, scaling of CMOS technology as per Moore's law has reached a serious bottleneck. Among the emerging technologies memristive devices can be promising for both memory as well as computing applications. Hybrid CMOS/memristor circuits with CMOL (CMOS + "Molecular") architecture have been proposed to combine the extremely high density of the memristive devices with the robustness of CMOS technology, leading to terabit-scale memory and extremely efficient computing paradigm. In this work, we demonstrate a hybrid 3D CMOL circuit with 2 layers of memristive crossbars monolithically integrated on a pre-fabricated CMOS substrate. The integrated crossbars can be fully operated through the underlying CMOS circuitry. The memristive devices in both layers exhibit analog switching behavior with controlled tunability and stable multi-level operation. We perform dot-product operations with the 2D and 3D memristive crossbars to demonstrate the applicability of such 3D CMOL hybrid circuits as a multiply-add engine. To the best of our knowledge this is the first demonstration of a functional 3D CMOL hybrid circuit.

A hybrid, coupled approach for modeling charged fluids from the nano to the mesoscale

DOE PAGES

Cheung, James; Frischknecht, Amalie L.; Perego, Mauro; ...

2017-07-20

Here, we develop and demonstrate a new, hybrid simulation approach for charged fluids, which combines the accuracy of the nonlocal, classical density functional theory (cDFT) with the efficiency of the Poisson–Nernst–Planck (PNP) equations. The approach is motivated by the fact that the more accurate description of the physics in the cDFT model is required only near the charged surfaces, while away from these regions the PNP equations provide an acceptable representation of the ionic system. We formulate the hybrid approach in two stages. The first stage defines a coupled hybrid model in which the PNP and cDFT equations act independentlymore » on two overlapping domains, subject to suitable interface coupling conditions. At the second stage we apply the principles of the alternating Schwarz method to the hybrid model by using the interface conditions to define the appropriate boundary conditions and volume constraints exchanged between the PNP and the cDFT subdomains. Numerical examples with two representative examples of ionic systems demonstrate the numerical properties of the method and its potential to reduce the computational cost of a full cDFT calculation, while retaining the accuracy of the latter near the charged surfaces.« less

A hybrid, coupled approach for modeling charged fluids from the nano to the mesoscale

NASA Astrophysics Data System (ADS)

Cheung, James; Frischknecht, Amalie L.; Perego, Mauro; Bochev, Pavel

2017-11-01

We develop and demonstrate a new, hybrid simulation approach for charged fluids, which combines the accuracy of the nonlocal, classical density functional theory (cDFT) with the efficiency of the Poisson-Nernst-Planck (PNP) equations. The approach is motivated by the fact that the more accurate description of the physics in the cDFT model is required only near the charged surfaces, while away from these regions the PNP equations provide an acceptable representation of the ionic system. We formulate the hybrid approach in two stages. The first stage defines a coupled hybrid model in which the PNP and cDFT equations act independently on two overlapping domains, subject to suitable interface coupling conditions. At the second stage we apply the principles of the alternating Schwarz method to the hybrid model by using the interface conditions to define the appropriate boundary conditions and volume constraints exchanged between the PNP and the cDFT subdomains. Numerical examples with two representative examples of ionic systems demonstrate the numerical properties of the method and its potential to reduce the computational cost of a full cDFT calculation, while retaining the accuracy of the latter near the charged surfaces.

A multiply-add engine with monolithically integrated 3D memristor crossbar/CMOS hybrid circuit

PubMed Central

Chakrabarti, B.; Lastras-Montaño, M. A.; Adam, G.; Prezioso, M.; Hoskins, B.; Cheng, K.-T.; Strukov, D. B.

2017-01-01

Silicon (Si) based complementary metal-oxide semiconductor (CMOS) technology has been the driving force of the information-technology revolution. However, scaling of CMOS technology as per Moore’s law has reached a serious bottleneck. Among the emerging technologies memristive devices can be promising for both memory as well as computing applications. Hybrid CMOS/memristor circuits with CMOL (CMOS + “Molecular”) architecture have been proposed to combine the extremely high density of the memristive devices with the robustness of CMOS technology, leading to terabit-scale memory and extremely efficient computing paradigm. In this work, we demonstrate a hybrid 3D CMOL circuit with 2 layers of memristive crossbars monolithically integrated on a pre-fabricated CMOS substrate. The integrated crossbars can be fully operated through the underlying CMOS circuitry. The memristive devices in both layers exhibit analog switching behavior with controlled tunability and stable multi-level operation. We perform dot-product operations with the 2D and 3D memristive crossbars to demonstrate the applicability of such 3D CMOL hybrid circuits as a multiply-add engine. To the best of our knowledge this is the first demonstration of a functional 3D CMOL hybrid circuit. PMID:28195239

A B-C-N hybrid porous sheet: an efficient metal-free visible-light absorption material.

PubMed

Lu, Ruifeng; Li, Feng; Salafranca, Juan; Kan, Erjun; Xiao, Chuanyun; Deng, Kaiming

2014-03-07

The polyphenylene network, known as porous graphene, is one of the most important and widely studied two-dimensional materials. As a potential candidate for photocatalysis and photovoltaic energy generation, its application has been limited by the low photocatalytic activity in the visible-light region. State-of-the-art hybrid density functional theory investigations are presented to show that an analogous B-C-N porous sheet outperforms the pristine polyphenylene network with significantly enhanced visible-light absorption. Compared with porous graphene, the calculated energy gap of the B-C-N hybrid crystal shrinks to 2.7 eV and the optical absorption peak remarkably shifts to the visible light region. The redox potentials of water splitting are well positioned in the middle of the band gap. Hybridizations among B_p, N_p and C_p orbitals are responsible for these findings. Valence and conduction band calculations indicate that the electrons and holes can be effectively separated, reducing charge recombination and improving the photoconversion efficiency. Moreover, the band gap and optical properties of the B-C-N hybrid porous sheet can be further finely engineered by external strain.

A hybrid, coupled approach for modeling charged fluids from the nano to the mesoscale

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

Cheung, James; Frischknecht, Amalie L.; Perego, Mauro

Here, we develop and demonstrate a new, hybrid simulation approach for charged fluids, which combines the accuracy of the nonlocal, classical density functional theory (cDFT) with the efficiency of the Poisson–Nernst–Planck (PNP) equations. The approach is motivated by the fact that the more accurate description of the physics in the cDFT model is required only near the charged surfaces, while away from these regions the PNP equations provide an acceptable representation of the ionic system. We formulate the hybrid approach in two stages. The first stage defines a coupled hybrid model in which the PNP and cDFT equations act independentlymore » on two overlapping domains, subject to suitable interface coupling conditions. At the second stage we apply the principles of the alternating Schwarz method to the hybrid model by using the interface conditions to define the appropriate boundary conditions and volume constraints exchanged between the PNP and the cDFT subdomains. Numerical examples with two representative examples of ionic systems demonstrate the numerical properties of the method and its potential to reduce the computational cost of a full cDFT calculation, while retaining the accuracy of the latter near the charged surfaces.« less

A density-functional study on the electronic and vibrational properties of layered antimony telluride.

PubMed

Stoffel, Ralf P; Deringer, Volker L; Simon, Ronnie E; Hermann, Raphaël P; Dronskowski, Richard

2015-03-04

We present a comprehensive survey of electronic and lattice-dynamical properties of crystalline antimony telluride (Sb2Te3). In a first step, the electronic structure and chemical bonding have been investigated, followed by calculations of the atomic force constants, phonon dispersion relationships and densities of states. Then, (macroscopic) physical properties of Sb2Te3 have been computed, namely, the atomic thermal displacement parameters, the Grüneisen parameter γ, the volume expansion of the lattice, and finally the bulk modulus B. We compare theoretical results from three popular and economic density-functional theory (DFT) approaches: the local density approximation (LDA), the generalized gradient approximation (GGA), and a posteriori dispersion corrections to the latter. Despite its simplicity, the LDA shows excellent performance for all properties investigated-including the Grüneisen parameter, which only the LDA is able to recover with confidence. In the absence of computationally more demanding hybrid DFT methods, the LDA seems to be a good choice for further lattice dynamical studies of Sb2Te3 and related layered telluride materials.

Theory of L -edge spectroscopy of strongly correlated systems

NASA Astrophysics Data System (ADS)

Lüder, Johann; Schött, Johan; Brena, Barbara; Haverkort, Maurits W.; Thunström, Patrik; Eriksson, Olle; Sanyal, Biplab; Di Marco, Igor; Kvashnin, Yaroslav O.

2017-12-01

X-ray absorption spectroscopy measured at the L edge of transition metals (TMs) is a powerful element-selective tool providing direct information about the correlation effects in the 3 d states. The theoretical modeling of the 2 p →3 d excitation processes remains to be challenging for contemporary ab initio electronic structure techniques, due to strong core-hole and multiplet effects influencing the spectra. In this work, we present a realization of the method combining the density-functional theory with multiplet ligand field theory, proposed in Haverkort et al. [Phys. Rev. B 85, 165113 (2012), 10.1103/PhysRevB.85.165113]. In this approach, a single-impurity Anderson model (SIAM) is constructed, with almost all parameters obtained from first principles, and then solved to obtain the spectra. In our implementation, we adopt the language of the dynamical mean-field theory and utilize the local density of states and the hybridization function, projected onto TM 3 d states, in order to construct the SIAM. The developed computational scheme is applied to calculate the L -edge spectra for several TM monoxides. A very good agreement between the theory and experiment is found for all studied systems. The effect of core-hole relaxation, hybridization discretization, possible extensions of the method as well as its limitations are discussed.

Oxygen holes and hybridization in the bismuthates

NASA Astrophysics Data System (ADS)

Khazraie, Arash; Foyevtsova, Kateryna; Elfimov, Ilya; Sawatzky, George A.

2018-02-01

Motivated by the recently renewed interest in the superconducting bismuth perovskites, we investigate the electronic structure of the parent compounds A BiO3 (A = Sr, Ba) using ab initio methods and tight-binding (TB) modeling. We use the density functional theory (DFT) in the local density approximation (LDA) to understand the role of various interactions in shaping the A BiO3 band structure near the Fermi level. It is established that interatomic hybridization involving Bi-6 s and O-2 p orbitals plays the most important role. Based on our DFT calculations, we derive a minimal TB model and demonstrate that it can describe the properties of the band structure as a function of lattice distortions, such as the opening of a charge gap with the onset of the breathing distortion and the associated condensation of holes onto a1 g-symmetric molecular orbitals formed by the O-2 pσ orbitals on collapsed octahedra. We also derive a single band model involving the hopping of an extended molecular orbital involving both Bi-6 s and a linear combination of six O-2 p orbitals which provides a very good description of the dispersion and band gaps of the low energy scale bands straddling the chemical potential.

Density Functional Studies of Stoichiometric Surfaces of Orthorhombic Hybrid Perovskite CH3NH3PbI3

DOE PAGES

Wang, Yun; Huang, Jingsong; Sumpter, Bobby G.; ...

2014-12-19

Organic/inorganic hybrid perovskite materials are highly attractive for dye-sensitized solar cells as demonstrated by their rapid advances in energy conversion efficiency. In this work, the structures, energetics, and electronic properties for a range of stoichiometric surfaces of the orthorhombic perovskite CH3NH3PbI3 are theoretically studied using density functional theory. Various possible spatially and constitutionally isomeric surfaces are considered by diversifying the spatial orientations and connectivities of surface Pb-I bonds. The comparison of the surface energies for the most stable configurations identified for various surfaces shows that the stabilities of stoichiometric surfaces are mainly dictated by the coordination numbers of surface atoms,more » which are directly correlated with the numbers of broken bonds. Additionally, Coulombic interactions between I anions and organic countercations on the surface also contribute to the stabilization. Electronic properties are compared between the most stable (100) surface and the bulk phase, showing generally similar features except for the lifted band degeneracy and the enhanced bandgap energy for the surface. These studies on the stoichiometric surfaces serve as the first step toward gaining a fundamental understanding of the interfacial properties in the current structural design of perovskite based solar cells, in order to achieve further breakthroughs in solar conversion efficiencies.« less

Importance of nonlocal electron correlation in the BaNiS2 semimetal from quantum oscillations studies

NASA Astrophysics Data System (ADS)

Klein, Yannick; Casula, Michele; Santos-Cottin, David; Audouard, Alain; Vignolles, David; Fève, Gwendal; Freulon, Vincent; Plaçais, Bernard; Verseils, Marine; Yang, Hancheng; Paulatto, Lorenzo; Gauzzi, Andrea

2018-02-01

By means of Shubnikov-de Haas and de Haas-van Alphen oscillations, and ab initio calculations, we have studied the Fermi surface of high-quality BaNiS2 single crystals, with mean free path l ˜400 Å . The angle and temperature dependence of quantum oscillations indicates a quasi-two-dimensional Fermi surface, made of an electronlike tube centered at Γ , and of four holelike cones, generated by Dirac bands, weakly dispersive in the out-of-plane direction. Ab initio electronic structure calculations, in the density functional theory framework, show that the inclusion of screened exchange is necessary to account for the experimental Fermi pockets. Therefore, the choice of the functional becomes crucial. A modified HSE hybrid functional with 7% of exact exchange outperforms both GGA and GGA +U density functionals, signaling the importance of nonlocal screened-exchange interactions in BaNiS2, and, more generally, in 3 d compensated semimetals.

Accurate first-principles structures and energies of diversely bonded systems from an efficient density functional

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

Sun, Jianwei; Remsing, Richard C.; Zhang, Yubo

2016-06-13

One atom or molecule binds to another through various types of bond, the strengths of which range from several meV to several eV. Although some computational methods can provide accurate descriptions of all bond types, those methods are not efficient enough for many studies (for example, large systems, ab initio molecular dynamics and high-throughput searches for functional materials). Here, we show that the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) within the density functional theory framework predicts accurate geometries and energies of diversely bonded molecules and materials (including covalent, metallic, ionic, hydrogen and vanmore » der Waals bonds). This represents a significant improvement at comparable efficiency over its predecessors, the GGAs that currently dominate materials computation. Often, SCAN matches or improves on the accuracy of a computationally expensive hybrid functional, at almost-GGA cost. SCAN is therefore expected to have a broad impact on chemistry and materials science.« less

Accurate first-principles structures and energies of diversely bonded systems from an efficient density functional.

PubMed

Sun, Jianwei; Remsing, Richard C; Zhang, Yubo; Sun, Zhaoru; Ruzsinszky, Adrienn; Peng, Haowei; Yang, Zenghui; Paul, Arpita; Waghmare, Umesh; Wu, Xifan; Klein, Michael L; Perdew, John P

2016-09-01

One atom or molecule binds to another through various types of bond, the strengths of which range from several meV to several eV. Although some computational methods can provide accurate descriptions of all bond types, those methods are not efficient enough for many studies (for example, large systems, ab initio molecular dynamics and high-throughput searches for functional materials). Here, we show that the recently developed non-empirical strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation (meta-GGA) within the density functional theory framework predicts accurate geometries and energies of diversely bonded molecules and materials (including covalent, metallic, ionic, hydrogen and van der Waals bonds). This represents a significant improvement at comparable efficiency over its predecessors, the GGAs that currently dominate materials computation. Often, SCAN matches or improves on the accuracy of a computationally expensive hybrid functional, at almost-GGA cost. SCAN is therefore expected to have a broad impact on chemistry and materials science.

Computation of indirect nuclear spin-spin couplings with reduced complexity in pure and hybrid density functional approximations.

PubMed

Luenser, Arne; Kussmann, Jörg; Ochsenfeld, Christian

2016-09-28

We present a (sub)linear-scaling algorithm to determine indirect nuclear spin-spin coupling constants at the Hartree-Fock and Kohn-Sham density functional levels of theory. Employing efficient integral algorithms and sparse algebra routines, an overall (sub)linear scaling behavior can be obtained for systems with a non-vanishing HOMO-LUMO gap. Calculations on systems with over 1000 atoms and 20 000 basis functions illustrate the performance and accuracy of our reference implementation. Specifically, we demonstrate that linear algebra dominates the runtime of conventional algorithms for 10 000 basis functions and above. Attainable speedups of our method exceed 6 × in total runtime and 10 × in the linear algebra steps for the tested systems. Furthermore, a convergence study of spin-spin couplings of an aminopyrazole peptide upon inclusion of the water environment is presented: using the new method it is shown that large solvent spheres are necessary to converge spin-spin coupling values.

Study of the effect of low-power pulse laser on arc plasma and magnesium alloy target in hybrid welding by spectral diagnosis technique

NASA Astrophysics Data System (ADS)

Liu, Liming; Hao, Xinfeng

2008-10-01

In order to study the effect of laser pulses on arc plasma and target metal in the hybrid welding process, the spectra of the plasmas in the welding process of magnesium alloys are analysed in this paper. The acquisition system of plasma spectra is set up and the spectral lines of welding plasma are acquired. Compared with tungsten-inert gas (TIG) welding, the intensities of the spectral lines of magnesium increase sharply while those of Ar decrease for strong evaporation and ionization of magnesium alloys in low-power laser/arc hybrid welding. The electron temperature and density are estimated by the Boltzmann plot method and the Stark broadening effect. The result shows that the electron temperature of arc plasma in the hybrid welding process is much lower than that in TIG welding, especially in the laser beam-affected zone. In contrast, the electron density of the plasma is enhanced. The influences of laser parameters on electron temperature are also studied. The changes in electron temperature and density indicate that the effect of laser pulse on the target metal is the dominant factor influencing the electron temperature and density in low-power laser/arc hybrid welding.

Lower hybrid to whistler mode conversion on a density striation

NASA Astrophysics Data System (ADS)

Camporeale, E.; Delzanno, G. L.; Colestock, P.

2012-10-01

When a wave packet composed of short wavelength lower hybrid modes traveling in an homogeneous plasma region encounters an inhomogeneity, it can resonantly excite long wavelength whistler waves via a linear mechanism known as mode conversion. An enhancement of lower hybrid/whistler activity has been often observed by sounding rockets and satellites in the presence of density depletions (striations) in the upper ionosphere. We address here the process of linear mode conversion of lower hybrid to whistler waves, mediated by a density striation, using a scalar-field formalism (in the limit of cold plasma linear theory) which we solve numerically. We show that the mode conversion can effectively transfer a large amount of energy from the short to the long wavelength modes. We also study how the efficiency scales by changing the properties (width and amplitude) of the density striation. We present a general criterion for the width of the striation that, if fulfilled, maximizes the conversion efficiency. Such a criterion could provide an interpretation of recent laboratory experiments carried out on the Large Plasma Device at UCLA.

Bulk plasma fragmentation in a C4F8 inductively coupled plasma: A hybrid modeling study

NASA Astrophysics Data System (ADS)

Zhao, Shu-Xia; Zhang, Yu-Ru; Gao, Fei; Wang, You-Nian; Bogaerts, Annemie

2015-06-01

A hybrid model is used to investigate the fragmentation of C4F8 inductive discharges. Indeed, the resulting reactive species are crucial for the optimization of the Si-based etching process, since they determine the mechanisms of fluorination, polymerization, and sputtering. In this paper, we present the dissociation degree, the density ratio of F vs. CxFy (i.e., fluorocarbon (fc) neutrals), the neutral vs. positive ion density ratio, details on the neutral and ion components, and fractions of various fc neutrals (or ions) in the total fc neutral (or ion) density in a C4F8 inductively coupled plasma source, as well as the effect of pressure and power on these results. To analyze the fragmentation behavior, the electron density and temperature and electron energy probability function (EEPF) are investigated. Moreover, the main electron-impact generation sources for all considered neutrals and ions are determined from the complicated C4F8 reaction set used in the model. The C4F8 plasma fragmentation is explained, taking into account many factors, such as the EEPF characteristics, the dominance of primary and secondary processes, and the thresholds of dissociation and ionization. The simulation results are compared with experiments from literature, and reasonable agreement is obtained. Some discrepancies are observed, which can probably be attributed to the simplified polymer surface kinetics assumed in the model.

Creating Hybrid Plasmas With Off-Axis ECCD for Radiating Divertor Studies in DIII-D

NASA Astrophysics Data System (ADS)

Petty, C. C.; Ferron, J. R.; Luce, T. C.; Osborne, T. H.; Petrie, T. W.; Turco, F.; Holcomb, C. T.; Thome, K. E.

2017-10-01

A long duration, high density, high power hybrid scenario has been developed for use in radiative divertor studies in DIII-D. Using 11.2 MW of co-NBI power and 3.4 MW of ECCD, with a total injected energy of up to 56 MJ, high performance hybrid plasmas with βN = 3.7 and H98y2 = 1.5 were created. The hybrid plasmas were fully non-inductive at densities of n 4.2 ×1019 m-3 with central ECCD, but the EC deposition needed to be moved to ρ = 0.45 to avoid the right-hand cutoff when the density was raised to n 5.8 ×1019 m-3 for radiative divertor studies. Although moving the EC deposition to ρ = 0.45 had the effect of dropping τE by 10%, the energy confinement time increased with higher density like τE n0.4, allowing high beta to be maintained. While the plasma current profile displays the usual self-organizing properties of hybrids - an anomalously broad profile with qmin >1 - local current drive can still have a measurable effect on stability, either positively or negatively. For example, hybrid discharges with radial ECH deposited at ρ = 0.45 proved to be more robustly stable to n = 1 modes (can be either a 1/1 or 2/1 mode) than similar discharges with co-ECCD at the same location. Interestingly, the large 1/1 mode had almost no effect on energy confinement but strongly degraded particle confinement; thus this mode needed to be suppressed to achieve the high pedestal densities required for radiative divertor studies. Work supported by USDOE under DE-FC02-04ER54698.

Preparation of an amide group-connected graphene-polyaniline nanofiber hybrid and its application in supercapacitors.

PubMed

Jianhua, Liu; Junwei, An; Yecheng, Zhou; Yuxiao, Ma; Mengliu, Li; Mei, Yu; Songmei, Li

2012-06-27

Polyaniline (PANI) nanofiber is grafted onto graphene to obtain a novel graphene-polyaniline (GP) hybrid. Graphene is activated using SOCl2 and reacts with PANI to form an amide group that intimately connects graphene and PANI. The existence of the amide group and its anchoring effect in the GP hybrid are confirmed and characterized by SEM, TEM, FT-IR, Raman, XPS and quantum chemistry analyses. Electrochemical tests reveal that the GP hybrid has high capacitance performances of 579.8 and 361.9 F g(-1) at current densities of 0.3 and 1 A g(-1). These values indicate superiority to materials interacted by van der Waals force. Long-term charge/discharge tests at high current densities show that the GP hybrid preserves 96% of its initial capacitance, demonstrating good electrochemical stability. The improved electrochemical performance suggests promising application of the GP hybrid in high-performance supercapacitors.

Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization

PubMed Central

Sándor, Mónika; Nistor, Cristina Lavinia; Szalontai, Gábor; Stoica, Rusandica; Nicolae, Cristian Andi; Alexandrescu, Elvira; Fazakas, József; Oancea, Florin; Donescu, Dan

2016-01-01

A series of aminopropyl-functionalized silica nanoparticles were prepared through a basic two step sol-gel process in water. Prior to being aminopropyl-functionalized, silica particles with an average diameter of 549 nm were prepared from tetraethyl orthosilicate (TEOS), using a Stöber method. In a second step, aminopropyl-silica particles were prepared by silanization with 3-aminopropyltriethoxysilane (APTES), added drop by drop to the sol-gel mixture. The synthesized amino-functionalized silica particles are intended to be used as supports for immobilization of humic acids (HA), through electrostatic bonds. Furthermore, by inserting beside APTES, unhydrolysable mono-, di- or trifunctional alkylsilanes (methyltriethoxy silane (MeTES), trimethylethoxysilane (Me3ES), diethoxydimethylsilane (Me2DES) and 1,2-bis(triethoxysilyl)ethane (BETES)) onto silica particles surface, the spacing of the free amino groups was intended in order to facilitate their interaction with HA large molecules. Two sorts of HA were used for evaluating the immobilization capacity of the novel aminosilane supports. The results proved the efficient functionalization of silica nanoparticles with amino groups and showed that the immobilization of the two tested types of humic acid substances was well achieved for all the TEOS/APTES = 20/1 (molar ratio) silica hybrids having or not having the amino functions spaced by alkyl groups. It was shown that the density of aminopropyl functions is low enough at this low APTES fraction and do not require a further spacing by alkyl groups. Moreover, all the hybrids having negative zeta potential values exhibited low interaction with HA molecules. PMID:28787834

Mott Transition of MnO under Pressure: A Comparison of Correlated Band Theories

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

Kasinathan, Deepa; Kunes, Jan; Koepernik, K

The electronic structure, magnetic moment, and volume collapse of MnO under pressure are obtained from four different correlated band theory methods; local density approximation+Hubbard U (LDA+U), pseudopotential self-interaction correction (pseudo-SIC), the hybrid functional (combined local exchange plus Hartree-Fock exchange), and the local spin density SIC (SIC-LSD) method. Each method treats correlation among the five Mn 3d orbitals (per spin), including their hybridization with three O 2p orbitals in the valence bands and their changes with pressure. The focus is on comparison of the methods for rock salt MnO (neglecting the observed transition to the NiAs structure in the 90-100 GPamore » range). Each method predicts a first-order volume collapse, but with variation in the predicted volume and critical pressure. Accompanying the volume collapse is a moment collapse, which for all methods is from high-spin to low-spin ((5/2){yields}(1/2)), not to nonmagnetic as the simplest scenario would have. The specific manner in which the transition occurs varies considerably among the methods: pseudo-SIC and SIC-LSD give insulator-to-metal, while LDA+U gives insulator-to-insulator and the hybrid method gives an insulator-to-semimetal transition. Projected densities of states above and below the transition are presented for each of the methods and used to analyze the character of each transition. In some cases the rhombohedral symmetry of the antiferromagnetically ordered phase clearly influences the character of the transition.« less

Hybrid nanomembranes for high power and high energy density supercapacitors and their yarn application.

PubMed

Lee, Jae Ah; Shin, Min Kyoon; Kim, Shi Hyeong; Kim, Seon Jeong; Spinks, Geoffrey M; Wallace, Gordon G; Ovalle-Robles, Raquel; Lima, Márcio D; Kozlov, Mikhail E; Baughman, Ray H

2012-01-24

We report mechanically robust, electrically conductive, free-standing, and transparent hybrid nanomembranes made of densified carbon nanotube sheets that were coated with poly(3,4-ethylenedioxythiophene) using vapor phase polymerization and their performance as supercapacitors. The hybrid nanomembranes with thickness of ~66 nm and low areal density of ~15 μg/cm(2)exhibited high mechanical strength and modulus of 135 MPa and 12.6 GPa, respectively. They also had remarkable shape recovery ability in liquid and at the liquid/air interface unlike previous carbon nanotube sheets. The hybrid nanomembrane attached on a current collector had volumetric capacitance of ~40 F/cm(3) at 100 V s(-1) (~40 and ~80 times larger than that of onion-like carbon measured at 100 V s(-1) and activated carbon measured at 20 V s(-1), respectively), and it showed rectangular shapes of cyclic voltammograms up to ~5 V s(-1). High mechanical strength and flexibility of the hybrid nanomembrane enabled twisting it into microsupercapacitor yarns with diameters of ~30 μm. The yarn supercapacitor showed stable cycling performance without a metal current collector, and its capacitance decrease was only ~6% after 5000 cycles. Volumetric energy and power density of the hybrid nanomembrane was ~70 mWh cm(-3) and ~7910 W cm(-3), and the yarn possessed the energy and power density of ~47 mWh cm(-3) and ~538 W cm(-3). © 2011 American Chemical Society

Ab-initio study on electronic properties of rocksalt SnAs

NASA Astrophysics Data System (ADS)

Babariya, Bindiya; Vaghela, M. V.; Gajjar, P. N.

2018-05-01

Within the frame work of Local Density Approximation of Exchange and Correlation, ab-initio method of density functional theory with Abinit code is used to compute electronic energy band structure, density of States and charge density of SnAs in rocksalt phase. Our result after optimization for lattice constant agrees with experimental value within 0.59% deviation. The computed electronic energy bands in high symmetry directions Γ→K→X→Γ→L→X→W→L→U shown metallic nature. The lowest band in the electronic band structure is showing band-gap approximately 1.70 eV from next higher band and no crossing between lowest two bands are seen. The density of states revels p-p orbit hybridization between Sn and As atoms. The spherical contour around Sn and As in the charge density plot represent partly ionic and partly covalent bonding. Fermi surface topology is the resultant effect of the single band crossing along L direction at Ef.

Optimizing Hill Seeding Density for High-Yielding Hybrid Rice in a Single Rice Cropping System in South China

PubMed Central

Wang, Danying; Chen, Song; Wang, Zaiman; Ji, Chenglin; Xu, Chunmei; Zhang, Xiufu; Chauhan, Bhagirath Singh

2014-01-01

Mechanical hill direct seeding of hybrid rice could be the way to solve the problems of high seeding rates and uneven plant establishment now faced in direct seeded rice; however, it is not clear what the optimum hill seeding density should be for high-yielding hybrid rice in the single-season rice production system. Experiments were conducted in 2010 and 2011 to determine the effects of hill seeding density (25 cm×15 cm, 25 cm×17 cm, 25 cm×19 cm, 25 cm×21 cm, and 25 cm×23 cm; three to five seeds per hill) on plant growth and grain yield of a hybrid variety, Nei2you6, in two fields with different fertility (soil fertility 1 and 2). In addition, in 2012 and 2013, comparisons among mechanical hill seeding, broadcasting, and transplanting were conducted with three hybrid varieties to evaluate the optimum seeding density. With increases in seeding spacing from 25 cm×15 cm to 25 cm×23 cm, productive tillers per hill increased by 34.2% and 50.0% in soil fertility 1 and 2. Panicles per m2 declined with increases in seeding spacing in soil fertility 1. In soil fertility 2, no difference in panicles per m2 was found at spacing ranging from 25 cm×17 cm to 25 cm×23 cm, while decreases in the area of the top three leaves and aboveground dry weight per shoot at flowering were observed. Grain yield was the maximum at 25 cm×17 cm spacing in both soil fertility fields. Our results suggest that a seeding density of 25 cm×17 cm was suitable for high-yielding hybrid rice. These results were verified through on-farm demonstration experiments, in which mechanical hill-seeded rice at this density had equal or higher grain yield than transplanted rice. PMID:25290342

Anharmonic Thermal Oscillations of the Electron Momentum Distribution in Lithium Fluoride

NASA Astrophysics Data System (ADS)

Erba, A.; Maul, J.; Itou, M.; Dovesi, R.; Sakurai, Y.

2015-09-01

Anharmonic thermal effects on the electron momentum distribution of a lithium fluoride single crystal are experimentally measured through high-resolution Compton scattering and theoretically modeled with ab initio simulations, beyond the harmonic approximation to the lattice potential, explicitly accounting for thermal expansion. Directional Compton profiles are measured at two different temperatures, 10 and 300 K, with a high momentum space resolution (0.10 a.u. in full width at half maximum), using synchrotron radiation. The effect of temperature on measured directional Compton profiles is clearly revealed by oscillations extending almost up to |p |=4 a .u . , which perfectly match those predicted from quantum-mechanical simulations. The wave-function-based Hartree-Fock method and three classes of the Kohn-Sham density functional theory (local-density, generalized-gradient, and hybrid approximations) are adopted. The lattice thermal expansion, as described with the quasiharmonic approach, is found to entirely account for the effect of temperature on the electron momentum density within the experimental accuracy.

Effect of electron Monte Carlo collisions on a hybrid simulation of a low-pressure capacitively coupled plasma

NASA Astrophysics Data System (ADS)

Hwang, Seok Won; Lee, Ho-Jun; Lee, Hae June

2014-12-01

Fluid models have been widely used and conducted successfully in high pressure plasma simulations where the drift-diffusion and the local-field approximation are valid. However, fluid models are not able to demonstrate non-local effects related to large electron energy relaxation mean free path in low pressure plasmas. To overcome this weakness, a hybrid model coupling electron Monte Carlo collision (EMCC) method with the fluid model is introduced to obtain precise electron energy distribution functions using pseudo-particles. Steady state simulation results by a one-dimensional hybrid model which includes EMCC method for the collisional reactions but uses drift-diffusion approximation for electron transport in a fluid model are compared with those of a conventional particle-in-cell (PIC) and a fluid model for low pressure capacitively coupled plasmas. At a wide range of pressure, the hybrid model agrees well with the PIC simulation with a reduced calculation time while the fluid model shows discrepancy in the results of the plasma density and the electron temperature.

First principles study of vibrational dynamics of ceria-titania hybrid clusters

NASA Astrophysics Data System (ADS)

Majid, Abdul; Bibi, Maryam

2017-04-01

Density functional theory based calculations were performed to study vibrational properties of ceria, titania, and ceria-titania hybrid clusters. The findings revealed the dominance of vibrations related to oxygen when compared to those of metallic atoms in the clusters. In case of hybrid cluster, the softening of normal modes related to exterior oxygen atoms in ceria and softening/hardening of high/low frequency modes related to titania dimmers are observed. The results calculated for monomers conform to symmetry predictions according to which three IR and three Raman active modes were detected for TiO2, whereas two IR active and one Raman active modes were observed for CeO2. The comparative analysis indicates that the hybrid cluster CeTiO4 contains simultaneous vibrational fingerprints of the component dimmers. The symmetry, nature of vibrations, IR and Raman activity, intensities, and atomic involvement in different modes of the clusters are described in detail. The study points to engineering of CeTiO4 to tailor its properties for technological visible region applications in photocatalytic and electrochemical devices.

The structures and electronic properties of zigzag silicene nanoribbons with periodically embedded with four- and eight-membered rings

NASA Astrophysics Data System (ADS)

Tan, Guiping; Lu, Junzhe; Zhu, Hengjiang; Li, Fangfang; Ma, Miaomiao; Wang, Xiaoning

2018-07-01

Using density functional theory (DFT), we have studied the structure of a zigzag silicene nanoribbons (SiNRs) with periodically embedded with four- and eight-membered rings, and studied their electronic properties by calculating its band structures and density of states (DOS). The results showed that the zigzag SiNRs have a sp2 hybridization, in addition, the band gap gradually decreased with the increase of the width by layer, and gradually changed from semiconductor properties to metal properties. The existence of vacancy defects increased the band gap and energies, but their positions could not change the structure and the electronic properties.

A Kernel-Free Particle-Finite Element Method for Hypervelocity Impact Simulation. Chapter 4

NASA Technical Reports Server (NTRS)

Park, Young-Keun; Fahrenthold, Eric P.

2004-01-01

An improved hybrid particle-finite element method has been developed for the simulation of hypervelocity impact problems. Unlike alternative methods, the revised formulation computes the density without reference to any kernel or interpolation functions, for either the density or the rate of dilatation. This simplifies the state space model and leads to a significant reduction in computational cost. The improved method introduces internal energy variables as generalized coordinates in a new formulation of the thermomechanical Lagrange equations. Example problems show good agreement with exact solutions in one dimension and good agreement with experimental data in a three dimensional simulation.

Sulfur-vacancy-dependent geometric and electronic structure of bismuth adsorbed on Mo S2

NASA Astrophysics Data System (ADS)

Park, Youngsin; Li, Nannan; Lee, Geunsik; Kim, Kwang S.; Kim, Ki-Jeong; Hong, Soon Cheol; Han, Sang Wook

2018-03-01

Through Bi deposition on the single-crystalline Mo S2 surface, we find that the density of the sulfur vacancy is a critical parameter for the growth of the crystalline Bi overlayer or cluster at room temperature. Also, the Mo S2 band structure is significantly modified near Γ due to the orbital hybridization with an adsorbed Bi monolayer. Our experimental observations and analysis in combination with density functional theory calculation suggest the importance of controlling the sulfur vacancy concentration in realizing an exotic quantum phase based on the van der Waals interface of Bi and Mo S2 .

Process quality engineering for bioreactor-driven manufacturing of tissue-engineered constructs for bone regeneration.

PubMed

Papantoniou Ir, Ioannis; Chai, Yoke Chin; Luyten, Frank P; Schrooten Ir, Jan

2013-08-01

The incorporation of Quality-by-Design (QbD) principles in tissue-engineering bioprocess development toward clinical use will ensure that manufactured constructs possess prerequisite quality characteristics addressing emerging regulatory requirements and ensuring the functional in vivo behavior. In this work, the QbD principles were applied on a manufacturing process step for the in vitro production of osteogenic three-dimensional (3D) hybrid scaffolds that involves cell matrix deposition on a 3D titanium (Ti) alloy scaffold. An osteogenic cell source (human periosteum-derived cells) cultured in a bioinstructive medium was used to functionalize regular Ti scaffolds in a perfusion bioreactor, resulting in an osteogenic hybrid carrier. A two-level three-factor fractional factorial design of experiments was employed to explore a range of production-relevant process conditions by simultaneously changing value levels of the following parameters: flow rate (0.5-2 mL/min), cell culture duration (7-21 days), and cell-seeding density (1.5×10(3)-3×10(3) cells/cm(2)). This approach allowed to evaluate the individual impact of the aforementioned process parameters upon key quality attributes of the produced hybrids, such as collagen production, mineralization level, and cell number. The use of a fractional factorial design approach helped create a design space in which hybrid scaffolds of predefined quality attributes may be robustly manufactured while minimizing the number of required experiments.

Large scale GW calculations

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

Govoni, Marco; Galli, Giulia

We present GW calculations of molecules, ordered and disordered solids and interfaces, which employ an efficient contour deformation technique for frequency integration and do not require the explicit evaluation of virtual electronic states nor the inversion of dielectric matrices. We also present a parallel implementation of the algorithm, which takes advantage of separable expressions of both the single particle Green’s function and the screened Coulomb interaction. The method can be used starting from density functional theory calculations performed with semilocal or hybrid functionals. The newly developed technique was applied to GW calculations of systems of unprecedented size, including water/semiconductor interfacesmore » with thousands of electrons.« less

Large Scale GW Calculations

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

Govoni, Marco; Galli, Giulia

We present GW calculations of molecules, ordered and disordered solids and interfaces, which employ an efficient contour deformation technique for frequency integration and do not require the explicit evaluation of virtual electronic states nor the inversion of dielectric matrices. We also present a parallel implementation of the algorithm which takes advantage of separable expressions of both the single particle Green's function and the screened Coulomb interaction. The method can be used starting from density functional theory calculations performed with semilocal or hybrid functionals. We applied the newly developed technique to GW calculations of systems of unprecedented size, including water/semiconductor interfacesmore » with thousands of electrons.« less

Large scale GW calculations

DOE PAGES

Govoni, Marco; Galli, Giulia

2015-01-12

We present GW calculations of molecules, ordered and disordered solids and interfaces, which employ an efficient contour deformation technique for frequency integration and do not require the explicit evaluation of virtual electronic states nor the inversion of dielectric matrices. We also present a parallel implementation of the algorithm, which takes advantage of separable expressions of both the single particle Green’s function and the screened Coulomb interaction. The method can be used starting from density functional theory calculations performed with semilocal or hybrid functionals. The newly developed technique was applied to GW calculations of systems of unprecedented size, including water/semiconductor interfacesmore » with thousands of electrons.« less

Quantum Chemistry Study of Cycloaddition Pathways for the Reaction of o-Benzyne with Fullerenes and Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Jaffe, Richard; Han, Jie; Langhoff, Stephen R. (Technical Monitor)

1997-01-01

Functionalization of fullerenes via the [2+2] cycloaddition reaction with o-benzyne has been demonstrated in the laboratory. In contrast, [2+4) cycloaddition products are formed when benzyne reacts with planar polycyclic aromatic hydrocarbons. Using density functional theory (DFT) calculations with Becke's hybrid functional and small contracted gaussian basis sets, we are able to reproduce these product preferences. The objective of this work is to explore the functionalization of carbon nanotubes. We have studied o-benzyne cycloaddition products with a [14,0] single-walled nanotube. We find both the [2+2] and [2+4] adducts to be stable, with the latter product being somewhat favored.

Hybrid braided 3-D scaffold for bioartificial liver assist devices.

PubMed

Hoque, M E; Mao, H Q; Ramakrishna, S

2007-01-01

Three-dimensional ex vivo hepatocyte culture is a tissue-engineering approach to improve the treatment of liver disease. The extracorporeal bioartificial liver (BAL) assists devices that are used in patients until they either recover or receive a liver transplant. The 3-D scaffold plays a key role in the design of bioreactor that is the most important component of the BAL. Presently available 3-D scaffolds used in BAL have shown good performance. However, existing scaffolds are considered to be less than ideal in terms of high-density cultures of hepatocytes maintaining long-term metabolic functions. This study aims to develop a 3-D hybrid scaffold for a BAL support system that would facilitate high-density hepatocyte anchorage with long-term metabolic functions. The scaffolds were fabricated by interlacing polyethylene terephthalate (PET) fibers onto the polysulfone hollow fibers utilizing a modern microbraiding technique. Scaffolds with various pore sizes and porosities were developed by varying braiding angle which was controlled by the gear ratio of the microbraiding machine. The morphological characteristics (pore size and porosity) of the scaffolds were found to be regulated by the gear ratio. Smaller braiding angle yields larger pore and higher porosity. On the other hand, a larger braiding angle causes smaller pore and lower porosity. In hepatocyte culture it was investigated how the morphological characteristics (pore size and porosity) of scaffolds influenced the cell anchorage and metabolic functions. Scaffolds with larger pores and higher porosity resulted in more cell anchorage and higher cellular functions, like albumin and urea secretion, compared to that of smaller pores and lower porosity.

Conceptual DFT Study of the Local Chemical Reactivity of the Colored BISARG Melanoidin and Its Protonated Derivative

PubMed Central

Frau, Juan; Glossman-Mitnik, Daniel

2018-01-01

This computational study assessed eight fixed RSH (range-separated hybrid) density functionals that include CAM-B3LYP, LC-ωPBE, M11, MN12SX, N12SX, ωB97, ωB97X, and ωB97XD related to the Def2TZVP basis sets together with the SMD solvation model in the calculation the molecular structure and reactivity properties of the BISARG intermediate melanoidin pigment (5-(2-(E)-(Z)-5-[(2-furyl)methylidene]-3-(4-acetylamino-4-carboxybutyl)-2-imino-1,3-dihydroimidazol-4-ylideneamino(E)-4-[(2-furyl)methylidene]-5-oxo-1H-imidazol-1-yl)-2-acetylaminovaleric acid) and its protonated derivative, BISARG(p). The chemical reactivity descriptors for the systems were calculated via the Conceptual Density Functional Theory. The choice of active sites applicable to nucleophilic, electrophilic as well as radical attacks were made by linking them with Fukui functions indices, electrophilic and nucleophilic Parr functions, and the condensed Dual Descriptor Δf(r). The study found the MN12SX and N12SX density functionals to be the most appropriate in predicting the chemical reactivity of the molecular systems under study starting from the knowledge of the HOMO, LUMO, and HOMO-LUMO gap energies. PMID:29765937

Random function representation of stationary stochastic vector processes for probability density evolution analysis of wind-induced structures

NASA Astrophysics Data System (ADS)

Liu, Zhangjun; Liu, Zenghui

2018-06-01

This paper develops a hybrid approach of spectral representation and random function for simulating stationary stochastic vector processes. In the proposed approach, the high-dimensional random variables, included in the original spectral representation (OSR) formula, could be effectively reduced to only two elementary random variables by introducing the random functions that serve as random constraints. Based on this, a satisfactory simulation accuracy can be guaranteed by selecting a small representative point set of the elementary random variables. The probability information of the stochastic excitations can be fully emerged through just several hundred of sample functions generated by the proposed approach. Therefore, combined with the probability density evolution method (PDEM), it could be able to implement dynamic response analysis and reliability assessment of engineering structures. For illustrative purposes, a stochastic turbulence wind velocity field acting on a frame-shear-wall structure is simulated by constructing three types of random functions to demonstrate the accuracy and efficiency of the proposed approach. Careful and in-depth studies concerning the probability density evolution analysis of the wind-induced structure have been conducted so as to better illustrate the application prospects of the proposed approach. Numerical examples also show that the proposed approach possesses a good robustness.

Conceptual DFT Study of the Local Chemical Reactivity of the Colored BISARG Melanoidin and Its Protonated Derivative.

PubMed

Frau, Juan; Glossman-Mitnik, Daniel

2018-01-01

This computational study assessed eight fixed RSH (range-separated hybrid) density functionals that include CAM-B3LYP, LC-ωPBE, M11, MN12SX, N12SX, ωB97, ωB97X, and ωB97XD related to the Def2TZVP basis sets together with the SMD solvation model in the calculation the molecular structure and reactivity properties of the BISARG intermediate melanoidin pigment (5-(2-(E)-(Z)-5-[(2-furyl)methylidene]-3-(4-acetylamino-4-carboxybutyl)-2-imino-1,3-dihydroimidazol-4-ylideneamino(E)-4-[(2-furyl)methylidene]-5-oxo-1H-imidazol-1-yl)-2-acetylaminovaleric acid) and its protonated derivative, BISARG(p). The chemical reactivity descriptors for the systems were calculated via the Conceptual Density Functional Theory. The choice of active sites applicable to nucleophilic, electrophilic as well as radical attacks were made by linking them with Fukui functions indices, electrophilic and nucleophilic Parr functions, and the condensed Dual Descriptor Δf( r ). The study found the MN12SX and N12SX density functionals to be the most appropriate in predicting the chemical reactivity of the molecular systems under study starting from the knowledge of the HOMO, LUMO, and HOMO-LUMO gap energies.

Size-dependent error of the density functional theory ionization potential in vacuum and solution

DOE PAGES

Sosa Vazquez, Xochitl A.; Isborn, Christine M.

2015-12-22

Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potentialmore » for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. As a result, in vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.« less

Size-dependent error of the density functional theory ionization potential in vacuum and solution

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

Sosa Vazquez, Xochitl A.; Isborn, Christine M., E-mail: cisborn@ucmerced.edu

2015-12-28

Density functional theory is often the method of choice for modeling the energetics of large molecules and including explicit solvation effects. It is preferable to use a method that treats systems of different sizes and with different amounts of explicit solvent on equal footing. However, recent work suggests that approximate density functional theory has a size-dependent error in the computation of the ionization potential. We here investigate the lack of size-intensivity of the ionization potential computed with approximate density functionals in vacuum and solution. We show that local and semi-local approximations to exchange do not yield a constant ionization potentialmore » for an increasing number of identical isolated molecules in vacuum. Instead, as the number of molecules increases, the total energy required to ionize the system decreases. Rather surprisingly, we find that this is still the case in solution, whether using a polarizable continuum model or with explicit solvent that breaks the degeneracy of each solute, and we find that explicit solvent in the calculation can exacerbate the size-dependent delocalization error. We demonstrate that increasing the amount of exact exchange changes the character of the polarization of the solvent molecules; for small amounts of exact exchange the solvent molecules contribute a fraction of their electron density to the ionized electron, but for larger amounts of exact exchange they properly polarize in response to the cationic solute. In vacuum and explicit solvent, the ionization potential can be made size-intensive by optimally tuning a long-range corrected hybrid functional.« less

Evaluation of exchange-correlation functionals for time-dependent density functional theory calculations on metal complexes.

PubMed

Holland, Jason P; Green, Jennifer C

2010-04-15

The electronic absorption spectra of a range of copper and zinc complexes have been simulated by using time-dependent density functional theory (TD-DFT) calculations implemented in Gaussian03. In total, 41 exchange-correlation (XC) functionals including first-, second-, and third-generation (meta-generalized gradient approximation) DFT methods were compared in their ability to predict the experimental electronic absorption spectra. Both pure and hybrid DFT methods were tested and differences between restricted and unrestricted calculations were also investigated by comparison of analogous neutral zinc(II) and copper(II) complexes. TD-DFT calculated spectra were optimized with respect to the experimental electronic absorption spectra by use of a Matlab script. Direct comparison of the performance of each XC functional was achieved both qualitatively and quantitatively by comparison of optimized half-band widths, root-mean-squared errors (RMSE), energy scaling factors (epsilon(SF)), and overall quality-of-fit (Q(F)) parameters. Hybrid DFT methods were found to outperform all pure DFT functionals with B1LYP, B97-2, B97-1, X3LYP, and B98 functionals providing the highest quantitative and qualitative accuracy in both restricted and unrestricted systems. Of the functionals tested, B1LYP gave the most accurate results with both average RMSE and overall Q(F) < 3.5% and epsilon(SF) values close to unity (>0.990) for the copper complexes. The XC functional performance in spin-restricted TD-DFT calculations on the zinc complexes was found to be slightly worse. PBE1PBE, mPW1PW91 and B1LYP gave the most accurate results with typical RMSE and Q(F) values between 5.3 and 7.3%, and epsilon(SF) around 0.930. These studies illustrate the power of modern TD-DFT calculations for exploring excited state transitions of metal complexes. 2009 Wiley Periodicals, Inc.

Pressure dependence of electron density distribution and d-p-π hybridization in titanate perovskite ferroelectrics

NASA Astrophysics Data System (ADS)

Yamanaka, Takamitsu; Nakamoto, Yuki; Ahart, Muhtar; Mao, Ho-kwang

2018-04-01

Electron density distributions of PbTi O3 , BaTi O3 , and SrTi O3 were determined by synchrotron x-ray powder diffraction up to 55 GPa at 300 K and ab initio quantum chemical molecular orbital (MO) calculations, together with a combination of maximum entropy method calculations. The intensity profiles of Bragg peaks reveal split atoms in both ferroelectric PbTi O3 and BaTi O3 , reflecting the two possible positions occupied by the Ti atom. The experimentally obtained atomic structure factor was used for the determination of the deformation in electron density and the d-p-π hybridization between dx z (and dy z) of Ti and px (and py) of O in the Ti-O bond. Ab initio MO calculations proved the change of the molecular orbital coupling and of Mulliken charges with a structure transformation. The Mulliken charge of Ti in the Ti O6 octahedron increased in the ionicity with increasing pressure in the cubic phase. The bonding nature is changed with a decrease in the hybridization of the Ti-O bond and the localization of the electron density with increasing pressure. The hybridization decreases with pressure and disappears in the cubic paraelectric phase, which has a much more localized electron density distribution.

Dirac cone pairs in silicene induced by interface Si-Ag hybridization: A first-principles effective band study

NASA Astrophysics Data System (ADS)

Lian, Chao; Meng, Sheng

2017-06-01

Using density functional theory combined with orbital-selective band unfolding techniques, we study the effective band structure of silicene (3 ×3 )/Ag(111) (4 ×4 ) structure. Consistent with the ARPES spectra recently obtained by [Feng et al. Proc. Natl. Acad. Sci. USA 113, 14656 (2016), 10.1073/pnas.1613434114], we observe six pairs of Dirac cones near the boundary of the Brillouin zone (BZ) of Ag (1 ×1 ) , while no Dirac cone is observed inside the BZ. Furthermore, we find that these Dirac cones are induced by the interfacial Si-Ag hybridization, mainly composed of Si pz orbitals and Ag s p bands, which is intrinsically different from the Dirac cones in free-standing silicene.

The electronic and optical properties of CH3NH3MoI3 perovskite

NASA Astrophysics Data System (ADS)

Kansara, Shivam; Sonvane, Yogesh; Gupta, Sanjeev K.

2018-05-01

In this work, a first-principles theoretical study of hybrid perovskite CH3NH3MoI3 is performed using PBE exchange-correlation approximations in density functional theory. The results of electronic band structure are 0.90 eV (M-point: Direct) and 0.60 eV (R-X point: Indirect), respectively. We have also calculated the dielectric properties such as real, imaginary, extension coefficient (K) and reflectivity (R) properties of hybrid perovskite CH3NH3MoI3. The low-bandgap molecules are used to absorb near-IR range and typically having a bandgap smaller than 1.6 eV. This is particularly attractive in organic photovoltaics (OPV), photodetectors (PDs), and ambipolar field-effect transistors (FETs).

Experimental and theoretical studies of a pyrazole-thiazolidin-2,4-di-one hybrid

NASA Astrophysics Data System (ADS)

Mushtaque, Md.; Avecilla, Fernando; Haque, Ashanul; Perwez, Ahmad; Khan, Md. Shahzad; Rizvi, M. Moshahid Alam

2017-08-01

The present work describes synthesis, characterization and biological evaluations of a hybrid compound 10 composed of two intriguing scaffolds pyrazole and thiazolidin-2,4-di-one. The title compound was obtained via multi-step reaction and characterized by a number of techniques (viz. IR, UV-Visible, 1H-NMR, 13C-NMR and MS) including X-ray crystallography. The structural and photophysical data of compound 10 were well supported by theoretical calculations performed at density functional (DFT) level. In-vitro anticancer studies on different human cancer cell lines indicated moderate to low activity of the compounds. The molecular target of the compound was predicted through in-silico studies. Finding of the studies are presented herein.

Polyurethane foam with multi walled carbon nanotubes/magnesium hybrid filler

NASA Astrophysics Data System (ADS)

Adnan, Sinar Arzuria; Zainuddin, Firuz; Zaidi, Nur Hidayah Ahmad; Akil, Hazizan Md.; Ahmad, Sahrim

2016-07-01

The purpose of this paper is to investigate the effect of multiwalled carbon nanotubes (MWCNTs)/magnesium (Mg) hybrid filler in polyurethane (PU) foams with different weight percentages (0.5 wt.% to 3.0 wt.%). The PU/MWCNTs/Mg foam composites were formed by reaction of based palm oil polyol (POP) with methylene diphenyl diisocyanate (MDI) with ratio 1:1.1 by weight. The foam properties were evaluated in density, morphology and compressive strength. The addition of 2.5 wt.% hybrid filler showed the higher density in 59.72 kg/m3 and thus contribute to the highest compressive strength at 1.76 MPa. The morphology show cell in closed structure and addition hybrid filler showed uneven structure.

Preliminary Study of a Hybrid Helicon-ECR Plasma Source

NASA Astrophysics Data System (ADS)

M. Hala, A.; Oksuz, L.; Ximing, Zhu

2016-08-01

A new type of hybrid discharge is experimentally investigated in this work. A helicon source and an electron cyclotron resonance (ECR) source were combined to produce plasma. As a preliminary study of this type of plasma, the optical emission spectroscopy (OES) method was used to obtain values of electron temperature and density under a series of typical conditions. Generally, it was observed that the electron temperature decreases and the electron density increases as the pressure increased. When increasing the applied power at a certain pressure, the average electron density at certain positions in the discharge does not increase significantly possibly due to the high degree of neutral depletion. Electron temperature increased with power in the hybrid mode. Possible mechanisms of these preliminary observations are discussed.

Wave generation by contaminant ions near a large spacecraft

NASA Technical Reports Server (NTRS)

Singh, N.

1993-01-01

Measurements from the space shuttle flights have revealed that a large spacecraft in a low earth orbit is accompanied by an extensive gas cloud which is primarily made up of water. The charge exchange between the water molecule and the ionospheric O(+) ions produces a water ion beam traversing downstream of the spacecraft. In this report we present results from a study on the generation of plasma waves by the interaction of the water ion beams with the ionospheric plasma. Since velocity distribution function is key to the understanding of the wave generation process, we have performed a test particle simulation to determine the nature of H2O(+) ions velocity distribution function. The simulations show that at the time scales shorter than the ion cyclotron period tau(sub c), the distribution function can be described by a beam. On the other hand, when the time scales are larger than tau(sub c), a ring distribution forms. A brief description of the linear instabilities driven by an ion beam streaming across a magnetic field in a plasma is presented. We have identified two types of instabilities occurring in low and high frequency bands; the low-frequency instability occurs over the frequency band from zero to about the lower hybrid frequency for a sufficiently low beam density. As the beam density increases, the linear instability occurs at decreasing frequencies below the lower-hybrid frequency. The high frequency instability occurs near the electron cyclotron frequency and its harmonics.

PdnCO (n = 1,2): accurate Ab initio bond energies, geometries, and dipole moments and the applicability of density functional theory for fuel cell modeling.

PubMed

Schultz, Nathan E; Gherman, Benjamin F; Cramer, Christopher J; Truhlar, Donald G

2006-11-30

Electrode poisoning by CO is a major concern in fuel cells. As interest in applying computational methods to electrochemistry is increasing, it is important to understand the levels of theory required for reliable treatments of metal-CO interactions. In this paper we justify the use of relativistic effective core potentials for the treatment of PdCO and hence, by inference, for metal-CO interactions where the predominant bonding mechanism is charge transfer. We also sort out key issues involving basis sets and we recommend that bond energies of 17.2, 43.3, and 69.4 kcal/mol be used as the benchmark bond energy for dissociation of Pd2 into Pd atoms, PdCO into Pd and CO, and Pd2CO into Pd2 and CO, respectively. We calculated the dipole moments of PdCO and Pd2CO, and we recommend benchmark values of 2.49 and 2.81 D, respectively. Furthermore, we tested 27 density functionals for this system and found that only hybrid density functionals can qualitatively and quantitatively predict the nature of the sigma-donation/pi-back-donation mechanism that is associated with the Pd-CO and Pd2-CO bonds. The most accurate density functionals for the systems tested in this paper are O3LYP, OLYP, PW6B95, and PBEh.

High resistivity in undoped CdTe: carrier compensation of Te antisites and Cd vacancies

NASA Astrophysics Data System (ADS)

Lindström, A.; Mirbt, S.; Sanyal, B.; Klintenberg, M.

2016-01-01

In this paper, we focus on the high resistivity of intentionally undoped CdTe, where the most prevalent defects are Cd vacancies and Te antisites. Our calculated formation energies lead to the conclusion that the Fermi energy of undoped CdTe is at midgap due to carrier compensation of Te antisites and Cd vacancies, which explains the experimentally observed high resistivity. We use density functional theory with the hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06) and show that the proper description of the native defects in general fails using the local density approximation (LDA) instead of HSE06. We conclude that LDA is insufficient to understand the high resistivity of undoped CdTe. We calculate the neutral and double acceptor state of the Te antisite to be intrinsic DX-centers.

Continuously controlled optical band gap in oxide semiconductor thin films

DOE PAGES

Herklotz, Andreas; Rus, Stefania Florina; Ward, Thomas Zac

2016-02-02

The optical band gap of the prototypical semiconducting oxide SnO 2 is shown to be continuously controlled through single axis lattice expansion of nanometric films induced by low-energy helium implantation. While traditional epitaxy-induced strain results in Poisson driven multidirectional lattice changes shown to only allow discrete increases in bandgap, we find that a downward shift in the band gap can be linearly dictated as a function of out-of-plane lattice expansion. Our experimental observations closely match density functional theory that demonstrates that uniaxial strain provides a fundamentally different effect on the band structure than traditional epitaxy-induced multiaxes strain effects. In conclusion,more » charge density calculations further support these findings and provide evidence that uniaxial strain can be used to drive orbital hybridization inaccessible with traditional strain engineering techniques.« less

Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model

DOE PAGES

Ulybyshev, Maksim; Winterowd, Christopher; Zafeiropoulos, Savvas

2017-11-09

Here in this article, we discuss the nontrivial collective charge excitations (plasmons) of the extended square lattice Hubbard model. Using a fully nonperturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly correlated phase. The momentum-resolved charge susceptibility also is computed on the basis of the Euclidean charge-density-density correlator. In agreement with previous extended dynamical mean-field theory studies, we find that, atmore » high strength of the electron-electron interaction, the plasmon dispersion develops two branches.« less

Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model

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

Ulybyshev, Maksim; Winterowd, Christopher; Zafeiropoulos, Savvas

Here in this article, we discuss the nontrivial collective charge excitations (plasmons) of the extended square lattice Hubbard model. Using a fully nonperturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly correlated phase. The momentum-resolved charge susceptibility also is computed on the basis of the Euclidean charge-density-density correlator. In agreement with previous extended dynamical mean-field theory studies, we find that, atmore » high strength of the electron-electron interaction, the plasmon dispersion develops two branches.« less

A density functional theory (DFT) and time-dependent density functional theory (TDDFT) study on optical transitions in oligo(p-phenylenevinylene)-fullerene dyads and the applicability to resonant energy transfer.

PubMed

Toivonen, Teemu L J; Hukka, Terttu I

2007-06-07

The optical transitions of three different size oligo(p-phenylenevinylene)-fullerene dyads (OPV(n)-MPC(60); n = 2-4) and of the corresponding separate molecules are studied using density functional theory (DFT) and time-dependent density functional theory. The DFT is used to determine the geometries and the electronic structures of the ground states. Transition energies and excited-state structures are obtained from the TDDFT calculations. Resonant energy transfer from OPV(n) to MPC(60) is also studied and the Fermi golden rule is used, along with two simple models to describe the electronic coupling to calculate the energy transfer rates. The hybrid-type PBE0 functional is used with a split-valence basis set augmented with a polarization function (SV(P)) in calculations and the calculated results are compared to the corresponding experimental results. The calculated PBE0 spectra of the OPV(n)-MPC(60) dyads correspond to the experimental spectra very well and are approximately sums of the absorption spectra of the separate OPV(n) and MPC(60) molecules. Also, the absorption energies of OPV(n) and MPC(60) and the emission energies of OPV(n) are predicted well with the PBE0 functional. The PBE0 calculated resonant energy transfer rates are in a good agreement with the experimental rates and show the existence of many possible pathways for energy transfer from the first excited singlet states of the OPV(n) molecules to the MPC(60) molecule.

Benchmarking the Performance of Exchange-Correlation Functionals for Predicting Two-Photon Absorption Strengths.

PubMed

Beerepoot, Maarten T P; Alam, Md Mehboob; Bednarska, Joanna; Bartkowiak, Wojciech; Ruud, Kenneth; Zaleśny, Robert

2018-06-15

The present work investigates the performance of exchange-correlation functionals in the prediction of two-photon absorption (2PA) strengths. For this purpose, we considered six common functionals used for studying 2PA processes and tested these on six organoboron chelates. The set consisted of two semilocal (PBE and BLYP), two hybrid (B3LYP and PBE0), and two range-separated (LC-BLYP and CAM-B3LYP) functionals. The RI-CC2 method was chosen as a reference level and was found to give results consistent with the experimental data that are available for three of the molecules considered. Of the six exchange-correlation functionals studied, only the range-separated functionals predict an ordering of the 2PA strengths that is consistent with experimental and RI-CC2 results. Even though the range-separated functionals predict correct relative trends, the absolute values for the 2PA strengths are underestimated by a factor of 2-6 for the molecules considered. An in-depth analysis, on the basis of the derived generalized few-state model expression for the 2PA strength for a coupled-cluster wave function, reveals that the problem with these functionals can be linked to underestimated excited-state dipole moments and, to a lesser extent, overestimated excitation energies. The semilocal and hybrid functionals exhibit less predictable errors and a variation in the 2PA strengths in disagreement with the reference results. The semilocal and hybrid functionals show smaller average errors than the range-separated functionals, but our analysis reveals that this is due to fortuitous error cancellation between excitation energies and the transition dipole moments. Our results constitute a warning against using currently available exchange-correlation functionals in the prediction of 2PA strengths and highlight the need for functionals that correctly describe the electron density of excited electronic states.

Molecular excited states from the SCAN functional

NASA Astrophysics Data System (ADS)

Tozer, David J.; Peach, Michael J. G.

2018-06-01

The performance of the strongly constrained and appropriately normed (SCAN) meta-generalised gradient approximation exchange-correlation functional is investigated for the calculation of time-dependent density-functional theory molecular excitation energies of local, charge-transfer and Rydberg character, together with the excited ? potential energy curve in H2. The SCAN results frequently resemble those obtained using a global hybrid functional, with either a standard or increased fraction of exact orbital exchange. For local excitations, SCAN can exhibit significant triplet instability problems, resulting in imaginary triplet excitation energies for a number of cases. The Tamm-Dancoff approximation offers a simple approach to improve the situation, but the excitation energies are still significantly underestimated. Understanding the origin of these (near)-triplet instabilities may provide useful insight into future functional development.

Hybrid density functional study of organic magnetic crystals: bi-metallic CrIII cyanides and rhombohedral C60

NASA Astrophysics Data System (ADS)

Chan, J. A.; Montanari, B.; Chan, W. L.; Harrison, N. M.

Periodic hybrid-exchange density functional theory calculations have been used to investigate the magnetic properties of two classes of organic magnets, namely the bi-metallic CrIII cyanides and the polymerized rhombohedral C60 fullerenes (Rh-C60). For the systems KMII[CrIII(CN)6] with M II=V, Mn, Ni and CrIII[CrIII(CN)6], the magnetic ordering energies, Mulliken populations, and spin density plots are reported for the optimized geometries. The qualitative nature of the magnetic coupling mechanism is consistent with that observed in previous unrestricted Hartree-Fock calculations, but the coupling energies computed here are significantly higher. The increased coupling is found to be a result of both changes in the geometry and the electronic structure resulting from the more reliable treatment of electronic exchange and correlation effects. The existence of long-range coupling between local spin moments is investigated in three different defective Rh-C60 structures: (i) a previously proposed prototype structure, where an atom is removed from the C60 cage; (ii) a related structure in which vacancies in nearby cages are brought closer together in pairs; and (iii) a structure where the intra-fullerene bond between the two inter-fullerene bonds is broken spontaneously after applying isotropic pressure to one layer of the Rh-C60 structure. All of these structures are characterized by low flat spin polarized bands at the Fermi edge and localized spin moments around the defects, but no evidence of long-range magnetic coupling is found.

Competing charge density wave and antiferromagnetism of metallic atom wires in GaN(10 1 ¯ ) and ZnO(10 1 ¯ )

NASA Astrophysics Data System (ADS)

Kang, Yoon-Gu; Kim, Sun-Woo; Cho, Jun-Hyung

2017-12-01

Low-dimensional electron systems often show a delicate interplay between electron-phonon and electron-electron interactions, giving rise to interesting quantum phases such as the charge density wave (CDW) and magnetism. Using the density-functional theory (DFT) calculations with the semilocal and hybrid exchange-correlation functionals as well as the exact-exchange plus correlation in the random-phase approximation (EX + cRPA), we systematically investigate the ground state of the metallic atom wires containing dangling-bond (DB) electrons, fabricated by partially hydrogenating the GaN(10 1 ¯0 ) and ZnO(10 1 ¯0 ) surfaces. We find that the CDW or antiferromagnetic (AFM) order has an electronic energy gain due to a band-gap opening, thereby being more stabilized compared to the metallic state. Our semilocal DFT calculation predicts that both DB wires in GaN(10 1 ¯0 ) and ZnO(10 1 ¯0 ) have the same CDW ground state, whereas the hybrid DFT and EX + cRPA calculations predict the AFM ground state for the former DB wire and the CDW ground state for the latter one. It is revealed that more localized Ga DB electrons in GaN(10 1 ¯0 ) prefer the AFM order, while less localized Zn DB electrons in ZnO(10 1 ¯0 ) the CDW formation. Our findings demonstrate that the drastically different ground states are competing in the DB wires created on the two representative compound semiconductor surfaces.

Nano-Sized Structurally Disordered Metal Oxide Composite Aerogels as High-Power Anodes in Hybrid Supercapacitors.

PubMed

Huang, Haijian; Wang, Xing; Tervoort, Elena; Zeng, Guobo; Liu, Tian; Chen, Xi; Sologubenko, Alla; Niederberger, Markus

2018-03-27

A general method for preparing nano-sized metal oxide nanoparticles with highly disordered crystal structure and their processing into stable aqueous dispersions is presented. With these nanoparticles as building blocks, a series of nanoparticles@reduced graphene oxide (rGO) composite aerogels are fabricated and directly used as high-power anodes for lithium-ion hybrid supercapacitors (Li-HSCs). To clarify the effect of the degree of disorder, control samples of crystalline nanoparticles with similar particle size are prepared. The results indicate that the structurally disordered samples show a significantly enhanced electrochemical performance compared to the crystalline counterparts. In particular, structurally disordered Ni x Fe y O z @rGO delivers a capacity of 388 mAh g -1 at 5 A g -1 , which is 6 times that of the crystalline sample. Disordered Ni x Fe y O z @rGO is taken as an example to study the reasons for the enhanced performance. Compared with the crystalline sample, density functional theory calculations reveal a smaller volume expansion during Li + insertion for the structurally disordered Ni x Fe y O z nanoparticles, and they are found to exhibit larger pseudocapacitive effects. Combined with an activated carbon (AC) cathode, full-cell tests of the lithium-ion hybrid supercapacitors are performed, demonstrating that the structurally disordered metal oxide nanoparticles@rGO||AC hybrid systems deliver high energy and power densities within the voltage range of 1.0-4.0 V. These results indicate that structurally disordered nanomaterials might be interesting candidates for exploring high-power anodes for Li-HSCs.

Multifunctional composites for energy storage

NASA Astrophysics Data System (ADS)

Shuvo, Mohammad Arif I.; Karim, Hasanul; Rajib, Md; Delfin, Diego; Lin, Yirong

2014-03-01

Electrochemical super-capacitors have become one of the most important topics in both academia and industry as novel energy storage devices because of their high power density, long life cycles, and high charge/discharge efficiency. Recently, there has been an increasing interest in the development of multifunctional structural energy storage devices such as structural super-capacitors for applications in aerospace, automobiles and portable electronics. These multifunctional structural super-capacitors provide lighter structures combining energy storage and load bearing functionalities. Due to their superior materials properties, carbon fiber composites have been widely used in structural applications for aerospace and automotive industries. Besides, carbon fiber has good electrical conductivity which will provide lower equivalent series resistance; therefore, it can be an excellent candidate for structural energy storage applications. Hence, this paper is focused on performing a pilot study for using nanowire/carbon fiber hybrids as building materials for structural energy storage materials; aiming at enhancing the charge/discharge rate and energy density. This hybrid material combines the high specific surface area of carbon fiber and pseudo-capacitive effect of metal oxide nanowires which were grown hydrothermally in an aligned fashion on carbon fibers. The aligned nanowire array could provide a higher specific surface area that leads to high electrode-electrolyte contact area and fast ion diffusion rates. Scanning Electron Microscopy (SEM) and XRay Diffraction (XRD) measurements were used for the initial characterization of this nanowire/carbon fiber hybrid material system. Electrochemical testing has been performed using a potentio-galvanostat. The results show that gold sputtered nanowire hybrid carbon fiber provides 65.9% better performance than bare carbon fiber cloth as super-capacitor.

Ab initio calculation of pentacene-PbSe hybrid interface for photovoltaic applications.

PubMed

Roy, P; Nguyen, Thao P

2016-07-21

We perform density functional theory (DFT) quantum chemical calculations for the pentacene-PbSe hybrid interface at both molecular and crystal levels. At the interface, the parallel orientation of pentacene on the PbSe surface is found to be the most favorable, analogous to a pentacene-gold interface. The molecule-surface distance and the value of charge transfer from one pentacene molecule to the PbSe surface are estimated at around 4.15 Å and 0.12 e(-) respectively. We found that, standard-LDA/GGA-PBE/hybrid/meta-GGA xc-functionals incorrectly determine the band gaps of both pentacene and PbSe and leads to a failed prediction of the energy alignment in this system. So, we use a relativistic G0W0 functional and accurately model the electronic properties of pentacene and PbSe in both bulk material and near the interface. An energy shift of 0.23 eV, due to the difference in work function at the interface was supplemented after a detailed analysis of the electrostatic potential. The highest occupied molecular orbital level of pentacene is 0.01 eV above PbSe while the lowest unoccupied molecular orbital of pentacene lies 1.70 eV above PbSe, allowing both electrons and holes to transfer along the donor-acceptor junction. Our results provide additional insights into the electronic structure properties of the pentacene-PbSe heterojunction and establish it as a promising and efficient candidate for photovoltaic applications.

Self-consistent Green's function embedding for advanced electronic structure methods based on a dynamical mean-field concept

NASA Astrophysics Data System (ADS)

Chibani, Wael; Ren, Xinguo; Scheffler, Matthias; Rinke, Patrick

2016-04-01

We present an embedding scheme for periodic systems that facilitates the treatment of the physically important part (here a unit cell or a supercell) with advanced electronic structure methods, that are computationally too expensive for periodic systems. The rest of the periodic system is treated with computationally less demanding approaches, e.g., Kohn-Sham density-functional theory, in a self-consistent manner. Our scheme is based on the concept of dynamical mean-field theory formulated in terms of Green's functions. Our real-space dynamical mean-field embedding scheme features two nested Dyson equations, one for the embedded cluster and another for the periodic surrounding. The total energy is computed from the resulting Green's functions. The performance of our scheme is demonstrated by treating the embedded region with hybrid functionals and many-body perturbation theory in the GW approach for simple bulk systems. The total energy and the density of states converge rapidly with respect to the computational parameters and approach their bulk limit with increasing cluster (i.e., computational supercell) size.

Final Technical Report for DE-SC0001878 [Theory and Simulation of Defects in Oxide Materials

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

Chelikowsky, James R.

2014-04-14

We explored a wide variety of oxide materials and related problems, including materials at the nanoscale and generic problems associated with oxide materials such as the development of more efficient computational tools to examine these materials. We developed and implemented methods to understand the optical and structural properties of oxides. For ground state properties, our work is predominantly based on pseudopotentials and density functional theory (DFT), including new functionals and going beyond the local density approximation (LDA): LDA+U. To study excited state properties (quasiparticle and optical excitations), we use time dependent density functional theory, the GW approach, and GW plusmore » Bethe-Salpeter equation (GW-BSE) methods based on a many-body Green function approaches. Our work focused on the structural, electronic, optical and magnetic properties of defects (such as oxygen vacancies) in hafnium oxide, titanium oxide (both bulk and clusters) and related materials. We calculated the quasiparticle defect states and charge transition levels of oxygen vacancies in monoclinic hafnia. we presented a milestone G0W0 study of two of the crystalline phases of dye-sensitized TiO{sub 2} clusters. We employed hybrid density functional theory to examine the electronic structure of sexithiophene/ZnO interfaces. To identify the possible effect of epitaxial strain on stabilization of the ferromagnetic state of LaCoO{sub 3} (LCO), we compare the total energy of the magnetic and nonmagnetic states of the strained theoretical bulk structure.« less

Utilizing upper hybrid resonance for high density plasma production and negative ion generation in a downstream region

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

Sahu, Debaprasad; Bhattacharjee, Sudeep

2012-09-15

Localized wave-induced resonances are created by microwaves launched directly into a multicusp (MC) plasma device in the k Up-Tack B mode, where k is the wave vector and B is the static magnetic field. The resonance zone is identified as upper hybrid resonance (UHR), and lies r = {approx}22 mm away from the MC boundary. Measurement of radial wave electric field intensity confirms the right hand cutoff of the wave (r = 22.5-32.1 mm) located near the UHR zone. A sharp rise in the corresponding electron temperature in the resonance region by {approx}13 eV from its value away from resonancemore » at r = 0, is favorable for the generation of vibrationally excited molecules of hydrogen. A transverse magnetic filter allows cold electrons ({approx}1-2 eV) to pass into the downstream region where they generate negative ions by dissociative attachment. Measurements of electron energy distribution function (EEDF) support the viewpoint. H{sup -} current density of {approx}0.26 mA/cm{sup 2} is obtained at a wave power density of {approx}3 W/cm{sup 2} at 2.0 mTorr pressure, which agrees reasonably well with results obtained from a steady state model using particle balance equations.« less

Hybrid Modeling of SiH4/Ar Discharge in a Pulse Modulated RF Capacitively Coupled Plasma

NASA Astrophysics Data System (ADS)

Xi-Feng, Wang; Yuan-Hong, Song; You-Nian, Wang; PSEG Team

2015-09-01

Pulsed plasmas have offered important advantages in future micro-devices, especially for electronegative gas plasmas. In this work, a one-dimensional fluid and Monte-Carlo (MC) hybrid model is developed to simulate SiH4/Ar discharge in a pulse modulated radio-frequency (RF) capacitively coupled plasma (CCP). Time evolution densities of different species, such as electrons, ions, radicals, are calculated, as well as the electron energy probability function (EEPF) which is obtained by a MC simulation. By pulsing the RF source, the electron energy distributions and plasma properties can be modulated by pulse frequency and duty cycle. High electron energy tails are obtained during power-on period, with the SiHx densities increasing rapidly mainly by SiH4 dissociation. As the RF power is off, the densities in the bulk region decrease rapidly owing to high energy electrons disappear, but increase near electrodes since diffusion without the confinement of high electric field, which can prolong the time of radials deposition on the plate. Especially, in the afterglow, the increase of negative ions near the electrodes results from cool electron attachment, which are good for film deposition. This work was supported by the National Natural Science Foundation of China (Grant No. 11275038).

Experimental investigation of density behaviors in front of the lower hybrid launcher in experimental advanced superconducting tokamak

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

Zhang, L.; Ding, B. J.; Li, M. H.

2013-06-15

A triple Langmuir probe is mounted on the top of the Lower Hybrid (LH) antenna to measure the electron density near the LH grills in Experimental Advanced Superconducting Tokamak. In this work, the LH power density ranges from 2.3 MWm{sup −2} to 10.3 MWm{sup −2} and the rate of puffing gas varies from 1.7 × 10{sup 20} el/s to 14 × 10{sup 20} el/s. The relation between the edge density (from 0.3 × n{sub e-cutoff} to 20 × n{sub e-cutoff}, where n{sub e-cutoff} is the cutoff density, n{sub e-cutoff} = 0.74 × 10{sup 17} m{sup −3} for 2.45 GHz lowermore » hybrid current drive) near the LH grill and the LH power reflection coefficients is investigated. The factors, including the gap between the LH grills and the last closed magnetic flux surface, line-averaged density, LH power, edge safety factor, and gas puffing, are analyzed. The experiments show that injection of LH power is beneficial for increasing edge density. Gas puffing is beneficial for increasing grill density but excess gas puffing is unfavorable for coupling and current drive.« less

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

PubMed

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

2018-04-26

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

The one-electron oxidation of a dithiolate molecule: the importance of chemical intuition.

PubMed

Bushnell, Eric A C; Burns, Thomas D; Boyd, Russell J

2014-05-14

A series of nine commonly used density functional methods were assessed to accurately predict the oxidation potential of the (C2H2S2(-2)/C2H2S2(•-)) redox couple. It was found that due to their greater tendency for charge delocalization the GGA functionals predict a structure where the radical electron is delocalized within the alkene backbone of C2H2S2(•-), whereas the hybrid functionals and the reference QCISD/cc-pVTZ predict that the radical electron remains localized on the sulfurs. However, chemical intuition suggests that the results obtained with the GGA functionals should be correct. Indeed, with the use of the geometries obtained at the HCTH/6-311++G(3df,3pd) level of theory both the QCISD and hybrid DFT methods yield a molecule with a delocalized electron. Notably, this new molecule lies at least 53 kJ mol(-1) lower in energy than the previously optimized one that had a localized radical. Using these new structures the calculated oxidation potential was found to be 2.71-2.97 V for the nine DFT functionals tested. The M06-L functional provided the best agreement with the QCISD/cc-pVTZ reference oxidation potential of 3.28 V.

Polyaniline-CuO hybrid nanocomposite with enhanced electrical conductivity

NASA Astrophysics Data System (ADS)

de Souza, Vânia S.; da Frota, Hidembergue O.; Sanches, Edgar A.

2018-02-01

A hybrid nanocomposite based on a polymer matrix constituted of Polyaniline Emeraldine-salt form (PANI-ES) reinforced by copper oxide II (CuO) particles was obtained by in situ polymerization. Structural, morphological and electrical properties of the pure materials and nanocomposite form were investigated. The presence of CuO particles in the nanocomposite material affected the natural alignment of the polymer chains. XRD technique allowed the visualization of the polymer amorphization in the nanocomposite form, suggesting an interaction between both phases. The FTIR spectra confirmed this molecular interaction due to the blue shift of the characteristic absorption peaks of PANI-ES in the nanocomposite form. SEM images revealed that the polymer nanofiber morphology was no longer observed in the nanocomposite. The CuO spherical particles are randomly dispersed in the polymer matrix. The density functional theory plus the Coulomb interaction method revealed a charge transfer from PANI to CuO slab. Moreover, the density of states (DOS) has revealed that the nanocomposite behaves as a metal. In agreement, the electrical conductivity showed an increase of 60% in the nanocomposite material.

Pondermotive versus mirror force in creation of the filamentary cavities in auroral plasma

NASA Technical Reports Server (NTRS)

Singh, Nagendra

1994-01-01

Recently rocket observations on spikelets of lower-hybrid waves along with strong density cavities and transversely heated ions were reported. The observed thin filamentary cavities oriented along the magnetic field in the auroral plasma have density depletions up to several tens of percent. These observations have been interpreted in terms of a theory for lower-hybrid wave condensation and collapse. The modulational instability leading to the wave consensation of the lower-hybrid waves yields only weak density perturbations, which cannot explain the above strong density depletions. The wave collapse theory is based on the nonlinear pondermotive force in a homogeneous ambient plasma and the density depletion is determined by the balance between the wave pressure (pondermotive force) and the plasma pressure. In the auroral plasma, the balance is achieved in a time tau(sub wc) equal to or less than 1 ms. It is shown here that the mirror force, acting on the transversely heated ions at a relatively long time scale, is an effective mechanism for creating the strong plasma cavities. We suggest that the process of wave condensation, through the pondermotive force causing generation of short wavelength waves from relatively long wavelength waves, is a dominant process until the former waves evolve and become effective in the transverse heating of ions. As soon as this happens, mirror force on ions becomes an important factor in the creation of the density cavities, which may further trap and enhance the waves. Results from a model of cavity formation by transverse ion heating show that the observed depletions in the density cavities can be produced by the heating rates determined by the observed wave amplitudes near the lower-hybrid frequency. It is found that the creation of a strong density cavity takes a few minutes.

The effects of density gradients on the convective amplification of upper hybrid waves in the magnetosphere

NASA Technical Reports Server (NTRS)

Engel, J.; Kennel, C.

1985-01-01

Intense (at least 10 mV/m) electrostatic plasma waves have been detected near the upper hybrid frequency between + or -50 deg MLAT during recent GEOS-1 crossings. Wave growth rate and convective amplification calculations were carried out in order to explain the occurrence of intense upper hybrid (IUH) events over such a wide range of latitudes. The effects of wave refractions were taken into account in the convective amplification calculations. Specific results are presented for the upper hybrid wave growth of an IUH event occurring at 10 deg MLAT. It is shown that a density gradient may be necessary to explain the observed amplification at 10 deg MLAT. At the equator, however, the long scale length of the magnetic field gradient enables large amplitudes to be attained without a density gradient. The results of a UH ray tracing analysis are discussed within the framework of current theories concerning magnetospheric continuum radiation.

Compact Stars with Sequential QCD Phase Transitions.

PubMed

Alford, Mark; Sedrakian, Armen

2017-10-20

Compact stars may contain quark matter in their interiors at densities exceeding several times the nuclear saturation density. We explore models of such compact stars where there are two first-order phase transitions: the first from nuclear matter to a quark-matter phase, followed at a higher density by another first-order transition to a different quark-matter phase [e.g., from the two-flavor color-superconducting (2SC) to the color-flavor-locked (CFL) phase]. We show that this can give rise to two separate branches of hybrid stars, separated from each other and from the nuclear branch by instability regions, and, therefore, to a new family of compact stars, denser than the ordinary hybrid stars. In a range of parameters, one may obtain twin hybrid stars (hybrid stars with the same masses but different radii) and even triplets where three stars, with inner cores of nuclear matter, 2SC matter, and CFL matter, respectively, all have the same mass but different radii.

Exact density functional and wave function embedding schemes based on orbital localization

NASA Astrophysics Data System (ADS)

Hégely, Bence; Nagy, Péter R.; Ferenczy, György G.; Kállay, Mihály

2016-08-01

Exact schemes for the embedding of density functional theory (DFT) and wave function theory (WFT) methods into lower-level DFT or WFT approaches are introduced utilizing orbital localization. First, a simple modification of the projector-based embedding scheme of Manby and co-workers [J. Chem. Phys. 140, 18A507 (2014)] is proposed. We also use localized orbitals to partition the system, but instead of augmenting the Fock operator with a somewhat arbitrary level-shift projector we solve the Huzinaga-equation, which strictly enforces the Pauli exclusion principle. Second, the embedding of WFT methods in local correlation approaches is studied. Since the latter methods split up the system into local domains, very simple embedding theories can be defined if the domains of the active subsystem and the environment are treated at a different level. The considered embedding schemes are benchmarked for reaction energies and compared to quantum mechanics (QM)/molecular mechanics (MM) and vacuum embedding. We conclude that for DFT-in-DFT embedding, the Huzinaga-equation-based scheme is more efficient than the other approaches, but QM/MM or even simple vacuum embedding is still competitive in particular cases. Concerning the embedding of wave function methods, the clear winner is the embedding of WFT into low-level local correlation approaches, and WFT-in-DFT embedding can only be more advantageous if a non-hybrid density functional is employed.

High density culture of white bass X striped bass fingerlings in raceways using power plant heated effluent

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

Collins, C.M.; Burton, G.L.; Schweinforth, R.L.

1983-06-01

White bass (Morone chrysops) X striped bass (M. saxatilis) hybrids weighing 1691/lb were initially stocked in five 24 ft/sup 3/ floating screen cages for 20 days. Hybrids averaging one inch in total length and 361 fish/lb were released in four 614 ft/sup 3/ concrete raceways. Two stocking densities, 2.6 and 5.1 fish/ft/sup 3/, were evaluated in the 94-day study using a flow rate of 300 gpm/raceway. Water temperatures averaged 79/sup 0/F and water quality was adequate throughout the production period. Fish were hand fed to satiation daily. Columnaris and Aeromonas hydrophila caused the most serious disease problems. Gas supersaturation wasmore » suspect in high mortality levels during cage culture of hybrid bass fry. Cannibalism may have been responsible for unaccountable losses prior to raceway stocking and at harvest. The study yielded 5773 hybrids weighing 658 lb. The high density treatment showed greater weight gain, average weight, average length and percent survival as well as improved food conversion. Results suggest that higher stocking densities and periodic grading may increase production and suppress cannibalism. 10 references, 3 figures, 3 tables.« less

Study of homogeneous bubble nucleation in liquid carbon dioxide by a hybrid approach combining molecular dynamics simulation and density gradient theory

NASA Astrophysics Data System (ADS)

Langenbach, K.; Heilig, M.; Horsch, M.; Hasse, H.

2018-03-01

A new method for predicting homogeneous bubble nucleation rates of pure compounds from vapor-liquid equilibrium (VLE) data is presented. It combines molecular dynamics simulation on the one side with density gradient theory using an equation of state (EOS) on the other. The new method is applied here to predict bubble nucleation rates in metastable liquid carbon dioxide (CO2). The molecular model of CO2 is taken from previous work of our group. PC-SAFT is used as an EOS. The consistency between the molecular model and the EOS is achieved by adjusting the PC-SAFT parameters to VLE data obtained from the molecular model. The influence parameter of density gradient theory is fitted to the surface tension of the molecular model. Massively parallel molecular dynamics simulations are performed close to the spinodal to compute bubble nucleation rates. From these simulations, the kinetic prefactor of the hybrid nucleation theory is estimated, whereas the nucleation barrier is calculated from density gradient theory. This enables the extrapolation of molecular simulation data to the whole metastable range including technically relevant densities. The results are tested against available experimental data and found to be in good agreement. The new method does not suffer from typical deficiencies of classical nucleation theory concerning the thermodynamic barrier at the spinodal and the bubble size dependence of surface tension, which is typically neglected in classical nucleation theory. In addition, the density in the center of critical bubbles and their surface tension is determined as a function of their radius. The usual linear Tolman correction to the capillarity approximation is found to be invalid.

Study of homogeneous bubble nucleation in liquid carbon dioxide by a hybrid approach combining molecular dynamics simulation and density gradient theory.

PubMed

Langenbach, K; Heilig, M; Horsch, M; Hasse, H

2018-03-28

A new method for predicting homogeneous bubble nucleation rates of pure compounds from vapor-liquid equilibrium (VLE) data is presented. It combines molecular dynamics simulation on the one side with density gradient theory using an equation of state (EOS) on the other. The new method is applied here to predict bubble nucleation rates in metastable liquid carbon dioxide (CO 2 ). The molecular model of CO 2 is taken from previous work of our group. PC-SAFT is used as an EOS. The consistency between the molecular model and the EOS is achieved by adjusting the PC-SAFT parameters to VLE data obtained from the molecular model. The influence parameter of density gradient theory is fitted to the surface tension of the molecular model. Massively parallel molecular dynamics simulations are performed close to the spinodal to compute bubble nucleation rates. From these simulations, the kinetic prefactor of the hybrid nucleation theory is estimated, whereas the nucleation barrier is calculated from density gradient theory. This enables the extrapolation of molecular simulation data to the whole metastable range including technically relevant densities. The results are tested against available experimental data and found to be in good agreement. The new method does not suffer from typical deficiencies of classical nucleation theory concerning the thermodynamic barrier at the spinodal and the bubble size dependence of surface tension, which is typically neglected in classical nucleation theory. In addition, the density in the center of critical bubbles and their surface tension is determined as a function of their radius. The usual linear Tolman correction to the capillarity approximation is found to be invalid.

Tuning the Seebeck effect in C60-based hybrid thermoelectric devices through temperature-dependent surface polarization and thermally-modulated interface dipoles.

PubMed

Liu, Yuchun; Xu, Ling; Zhao, Chen; Shao, Ming; Hu, Bin

2017-06-07

Fullerene (C 60 ) is an important n-type organic semiconductor with high electron mobility and low thermal conductivity. In this work, we report the experimental results on the tunable Seebeck effect of C 60 hybrid thin-film devices by adopting different oxide layers. After inserting n-type high-dielectric constant titanium oxide (TiO x ) and zinc oxide (ZnO) layers, we observed a significantly enhanced n-type Seebeck effect in oxide/C 60 hybrid devices with Seebeck coefficients of -5.8 mV K -1 for TiO x /C 60 and -2.08 mV K -1 for ZnO/C 60 devices at 100 °C, compared with the value of -400 μV K -1 for the pristine C 60 device. However, when a p-type nickel oxide (NiO) layer is inserted, the C 60 hybrid devices show a p-type to n-type Seebeck effect transition when the temperature increases. The remarkable Seebeck effect and change in Seebeck coefficient in different oxide/C 60 hybrid devices can be attributed to two reasons: the temperature-dependent surface polarization difference and thermally-dependent interface dipoles. Firstly, the surface polarization difference due to temperature-dependent electron-phonon coupling can be enhanced by inserting an oxide layer and functions as an additional driving force for the Seebeck effect development. Secondly, thermally-dependent interface dipoles formed at the electrode/oxide interface play an important role in modifying the density of interface states and affecting the charge diffusion in hybrid devices. The surface polarization difference and interface dipoles function in the same direction in hybrid devices with TiO x and ZnO dielectric layers, leading to enhanced n-type Seebeck effect, while the surface polarization difference and interface dipoles generate the opposite impact on electron diffusion in ITO/NiO/C 60 /Al, leading to a p-type to n-type transition in the Seebeck effect. Therefore, inserting different oxide layers could effectively modulate the Seebeck effect of C 60 -based hybrid devices through the surface polarization difference and thermally-dependent interface dipoles, which represents an effective approach to tune the vertical Seebeck effect in organic functional devices.

Temperature-controlled microintaglio printing for high-resolution micropatterning of RNA molecules.

PubMed

Kobayashi, Ryo; Biyani, Manish; Ueno, Shingo; Kumal, Subhashini Raj; Kuramochi, Hiromi; Ichiki, Takanori

2015-05-15

We have developed an advanced microintaglio printing method for fabricating fine and high-density micropatterns and applied it to the microarraying of RNA molecules. The microintaglio printing of RNA reported here is based on the hybridization of RNA with immobilized complementary DNA probes. The hybridization was controlled by switching the RNA conformation via the temperature, and an RNA microarray with a diameter of 1.5 µm and a density of 40,000 spots/mm(2) with high contrast was successfully fabricated. Specifically, no size effects were observed in the uniformity of patterned signals over a range of microarray feature sizes spanning one order of magnitude. Additionally, we have developed a microintaglio printing method for transcribed RNA microarrays on demand using DNA-immobilized magnetic beads. The beads were arrayed on wells fabricated on a printing mold and the wells were filled with in vitro transcription reagent and sealed with a DNA-immobilized glass substrate. Subsequently, RNA was in situ synthesized using the bead-immobilized DNA as a template and printed onto the substrate via hybridization. Since the microintaglio printing of RNA using DNA-immobilized beads enables the fabrication of a microarray of spots composed of multiple RNA sequences, it will be possible to screen or analyze RNA functions using an RNA microarray fabricated by temperature-controlled microintaglio printing (TC-µIP). Copyright © 2014 Elsevier B.V. All rights reserved.

Alignment of Gold Nanoparticle-Decorated DNA Origami Nanotubes: Substrate Prepatterning versus Molecular Combing.

PubMed

Teschome, Bezu; Facsko, Stefan; Gothelf, Kurt V; Keller, Adrian

2015-11-24

DNA origami has become an established technique for designing well-defined nanostructures with any desired shape and for the controlled arrangement of functional nanostructures with few nanometer resolution. These unique features make DNA origami nanostructures promising candidates for use as scaffolds in nanoelectronics and nanophotonics device fabrication. Consequently, a number of studies have shown the precise organization of metallic nanoparticles on various DNA origami shapes. In this work, we fabricated large arrays of aligned DNA origami decorated with a high density of gold nanoparticles (AuNPs). To this end, we first demonstrate the high-yield assembly of high-density AuNP arrangements on DNA origami adsorbed to Si surfaces with few unbound background nanoparticles by carefully controlling the concentrations of MgCl2 and AuNPs in the hybridization buffer and the hybridization time. Then, we evaluate two methods, i.e., hybridization to prealigned DNA origami and molecular combing in a receding meniscus, with respect to their potential to yield large arrays of aligned AuNP-decorated DNA origami nanotubes. Because of the comparatively low MgCl2 concentration required for the efficient immobilization of the AuNPs, the prealigned DNA origami become mobile and displaced from their original positions, thereby decreasing the alignment yield. This increased mobility, on the other hand, makes the adsorbed origami susceptible to molecular combing, and a total alignment yield of 86% is obtained in this way.

Active-passive hybrid piezoelectric actuators for high-precision hard disk drive servo systems

NASA Astrophysics Data System (ADS)

Chan, Kwong Wah; Liao, Wei-Hsin

2006-03-01

Positioning precision is crucial to today's increasingly high-speed, high-capacity, high data density, and miniaturized hard disk drives (HDDs). The demand for higher bandwidth servo systems that can quickly and precisely position the read/write head on a high track density becomes more pressing. Recently, the idea of applying dual-stage actuators to track servo systems has been studied. The push-pull piezoelectric actuated devices have been developed as micro actuators for fine and fast positioning, while the voice coil motor functions as a large but coarse seeking. However, the current dual-stage actuator design uses piezoelectric patches only without passive damping. In this paper, we propose a dual-stage servo system using enhanced active-passive hybrid piezoelectric actuators. The proposed actuators will improve the existing dual-stage actuators for higher precision and shock resistance, due to the incorporation of passive damping in the design. We aim to develop this hybrid servo system not only to increase speed of track seeking but also to improve precision of track following servos in HDDs. New piezoelectrically actuated suspensions with passive damping have been designed and fabricated. In order to evaluate positioning and track following performances for the dual-stage track servo systems, experimental efforts are carried out to implement the synthesized active-passive suspension structure with enhanced piezoelectric actuators using a composite nonlinear feedback controller.

Tunable Bifunctional Activity of Mnx Co3-x O4 Nanocrystals Decorated on Carbon Nanotubes for Oxygen Electrocatalysis.

PubMed

Zhao, Tingting; Gadipelli, Srinivas; He, Guanjie; Ward, Matthew J; Do, David; Zhang, Peng; Guo, Zhengxiao

2018-04-25

Noble-metal-free electrocatalysts are attractive for cathodic oxygen catalysis in alkaline membrane fuel cells, metal-air batteries, and electrolyzers. However, much of the structure-activity relationship is poorly understood. Herein, the comprehensive development of manganese cobalt oxide/nitrogen-doped multiwalled carbon nanotube hybrids (Mn x Co 3-x O 4 @NCNTs) is reported for highly reversible oxygen reduction and evolution reactions (ORR and OER, respectively). The hybrid structures are rationally designed by fine control of surface chemistry and synthesis conditions, including tuning of functional groups at surfaces, congruent growth of nanocrystals with controllable phases and particle sizes, and ensuring strong coupling across catalyst-support interfaces. Electrochemical tests reveal distinctly different oxygen catalytic activities among the hybrids, Mn x Co 3-x O 4 @NCNTs. Nanocrystalline MnCo 2 O 4 @NCNTs (MCO@NCNTs) hybrids show superior ORR activity, with a favorable potential to reach 3 mA cm -2 and a high current density response, equivalent to that of the commercial Pt/C standard. Moreover, the hybrid structure exhibits tunable and durable catalytic activities for both ORR and OER, with a lowest overall potential of 0.93 V. It is clear that the long-term electrochemical activities can be ensured by rational design of hybrid structures from the nanoscale. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Quantum-Inspired Maximizer

NASA Technical Reports Server (NTRS)

Zak, Michail

2008-01-01

A report discusses an algorithm for a new kind of dynamics based on a quantum- classical hybrid-quantum-inspired maximizer. The model is represented by a modified Madelung equation in which the quantum potential is replaced by different, specially chosen 'computational' potential. As a result, the dynamics attains both quantum and classical properties: it preserves superposition and entanglement of random solutions, while allowing one to measure its state variables, using classical methods. Such optimal combination of characteristics is a perfect match for quantum-inspired computing. As an application, an algorithm for global maximum of an arbitrary integrable function is proposed. The idea of the proposed algorithm is very simple: based upon the Quantum-inspired Maximizer (QIM), introduce a positive function to be maximized as the probability density to which the solution is attracted. Then the larger value of this function will have the higher probability to appear. Special attention is paid to simulation of integer programming and NP-complete problems. It is demonstrated that the problem of global maximum of an integrable function can be found in polynomial time by using the proposed quantum- classical hybrid. The result is extended to a constrained maximum with applications to integer programming and TSP (Traveling Salesman Problem).

Lower Hybrid Solitary Structures

NASA Technical Reports Server (NTRS)

Schuck, Peter W.

2011-01-01

Lower hybrid solitary structures (LHSS) have been observed by sounding rockets in the auroral ionosphere for over a decade and a half. LHSS are spatial structures embedded in space plasmas containing ambient whistler mode hiss. They are characterized by a density depletion of a few percent to several tens of percent in which electric fields near, both above and below, the lower hybrid resonance are more intense than the background fields by a factor of three to five. LHSS have dimensions across the magnetic field of a few to many thermal ion gyroradii, usually 10-100 meters and a density profile that is Gaussian and consistent with cylindrical symmetry. Along the magnetic field the dimensions are estimated to be several kilometers to several hundred kilometers. Electric field interferometry reveals that the phase fronts of LHSS electric fields rotate azimuthally within the density depletions; right-hand above the lower hybrid resonance and left-hand below the lower hybrid resonance [Pincon et al., 1997; Schuck et al., 1998; Bonnell et al., 1998; Tjulin et al., 2003; Schuck et al., 2003]. The description of this phenomena was driven by the observations the Cornell University sounding rocket program headed by the late Paul Kintner.

Phonon properties and slow organic-to-inorganic sub-lattice thermalization in hybrid perovskites

NASA Astrophysics Data System (ADS)

Chan, Maria; Chang, Angela; Xia, Yi; Sadasivam, Sridhar; Guo, Peijun; Kinaci, Alper; Lin, Hao-Wu; Darancet, Pierre; Schaller, Richard

Organic-inorganic hybrid perovskite halide compounds have been investigated extensively for photovoltaics (PVs) and related applications. The thermal transport properties of hybrid perovskites, including phonon-carrier and phonon-phonon interactions, are of significance for their PV and solar thermoelectric applications. The interlocking organic and inorganic sublattices can be thought of as an extreme form of nanostructuring. A result of this nanostructuring is the large gap in phonon frequencies between the organic and inorganic sublattices, which is expected to create bottlenecks in phonon equilibration. In this work, we use a combination of ultrafast spectroscopy including photoluminescence and transient absorption, as well as first principles density functional theory (DFT), ab initio molecular dynamics calculations, phonon lifetimes derived from DFT force constants, and non-equilibrium phonon dynamics accounting for phonon lifetimes, to determine the phonon and charge interaction processes. We find evidence that thermalization of carriers occur at an atypically slow 50-100 ps time scale owing to the complex interplay between electronic and phonon excitations.

Revealing the properties of defects formed by CH3NH2 molecules in organic-inorganic hybrid perovskite MAPbBr3

NASA Astrophysics Data System (ADS)

Wang, Ji; Zhang, Ao; Yan, Jun; Li, Dan; Chen, Yunlin

2017-03-01

The properties of defects in organic-inorganic hybrid perovskite are widely studied from the first-principles calculation. However, the defects of methylamine (methylamine = CH3NH2), which would be easily formed during the preparation of the organic-inorganic hybrid perovskite, are rarely investigated. Thermodynamic properties as well as defect states of methylamine embedded MAPbX3 (MA = methyl-ammonium = CH3NH3, X = Br, I) are studied based on first-principles calculations of density functional theory. It was found that there is a shallow defect level near the highest occupied molecular orbital, which induced by the interstitial methylamine defect in MAPbBr3, will lead to an increase of photoluminescence. The calculation results showed that interstitial defect states of methylamine may move deeper due to the interaction between methylamine molecules and methyl-ammonium cations. It was also showed that the interstitial methylamine defect is stable at room temperature, and the defect can be removed easily by annealing.

Rashba and Dresselhaus Effects in Hybrid Organic-Inorganic Perovskites: From Basics to Devices.

PubMed

Kepenekian, Mikaël; Robles, Roberto; Katan, Claudine; Sapori, Daniel; Pedesseau, Laurent; Even, Jacky

2015-12-22

We use symmetry analysis, density functional theory calculations, and k·p modeling to scrutinize Rashba and Dresselhaus effects in hybrid organic-inorganic halide perovskites. These perovskites are at the center of a recent revolution in the field of photovoltaics but have also demonstrated potential for optoelectronic applications such as transistors and light emitters. Due to a large spin-orbit coupling of the most frequently used metals, they are also predicted to offer a promising avenue for spin-based applications. With an in-depth inspection of the electronic structures and bulk lattice symmetries of a variety of systems, we analyze the origin of the spin splitting in two- and three-dimensional hybrid perovskites. It is shown that low-dimensional nanostructures made of CH3NH3PbX3 (X = I, Br) lead to spin splittings that can be controlled by an applied electric field. These findings further open the door for a perovskite-based spintronics.

Templated assembly of photoswitches significantly increases the energy-storage capacity of solar thermal fuels.

PubMed

Kucharski, Timothy J; Ferralis, Nicola; Kolpak, Alexie M; Zheng, Jennie O; Nocera, Daniel G; Grossman, Jeffrey C

2014-05-01

Large-scale utilization of solar-energy resources will require considerable advances in energy-storage technologies to meet ever-increasing global energy demands. Other than liquid fuels, existing energy-storage materials do not provide the requisite combination of high energy density, high stability, easy handling, transportability and low cost. New hybrid solar thermal fuels, composed of photoswitchable molecules on rigid, low-mass nanostructures, transcend the physical limitations of molecular solar thermal fuels by introducing local sterically constrained environments in which interactions between chromophores can be tuned. We demonstrate this principle of a hybrid solar thermal fuel using azobenzene-functionalized carbon nanotubes. We show that, on composite bundling, the amount of energy stored per azobenzene more than doubles from 58 to 120 kJ mol(-1), and the material also maintains robust cyclability and stability. Our results demonstrate that solar thermal fuels composed of molecule-nanostructure hybrids can exhibit significantly enhanced energy-storage capabilities through the generation of template-enforced steric strain.

Hierarchical heterostructure of MoS2 flake anchored on TiO2 sphere for supercapacitor application

NASA Astrophysics Data System (ADS)

Chanda, K.; Thakur, S.; Maiti, S.; Acharya, A.; Paul, T.; Besra, N.; Sarkar, S.; Das, A.; Sardar, K.; Chattopadhyay, K. K.

2018-05-01

Hierarchical architectures realized via rational coupling of several components not only boast synergy driven raised functionality compared to their structural constituents also exhibit noble interface phenomena, thus made them significantly pertinent from research and technological point of view. Here in, geometrically intricate hierarchical nanoform constituting MoS2 nanoflakes anchored on TiO2 sphere was realized via two steps hydrothermal protocol. Initially TiO2 sphere was synthesized using titanium isopropoxide assisted hydrothermal route followed by which the sphere was used as scaffold for secondary growth of MoS2. As synthesized hybrid sample displayed much improved electrochemical behavior than pristine TiO2 sphere. Assessed value of specific capacitance for the hybrid is found to 152.22 F/g at current density of 0.1A/g which is 30 fold than TiO2 sphere. This electrochemical performance enhancement can be accredited to high surface area of the hybrid sample.

New resonances from the coherence of Auger and intercoulombic (ICD) processes in the photoionization of endohedral fullerenes

NASA Astrophysics Data System (ADS)

Chakraborty, Himadri; Wise, Jacob; de, Ruma; Javani, Mohammad; Manson, Steve; Madjet, Mohamed

2014-05-01

Considering the photoionization of Ar@C60 , we predict resonant femtosecond decays of both Ar and C60 vacancies through the continua of atom-fullerene hybrid final states. The resulting resonances emerge from the interference between simultaneous autoionizing and intercoulombic decay (ICD) processes. For Ar 3s --> np excitations, these resonances are far stronger than the Ar-to-C60 resonant ICDs, while for C60 excitations they are strikingly larger than the corresponding Auger features. The results indicate the power of hybridization to enhance decay rates, and modify lifetimes and line profiles. These decays are also likely to exist generally in the ionization of molecules, nano-dimers and -polymers, and fullerene onions that support hybridized electrons as well. A jellium based time-dependent local density approximation (TDLDA), with the Leeuwen and Baerends exchange-correlation functional to produce accurate asymptotic behavior, is employed to calculate the dynamical response of the system to the photon field.

Hybrid structure of polyaniline/ZnO nanograss and its application in dye-sensitized solar cell with performance improvement

NASA Astrophysics Data System (ADS)

Zhu, Shibu; Wei, Wei; Chen, Xiangnan; Jiang, Man; Zhou, Zuowan

2012-06-01

Polyaniline (PANI) hybridized ZnO photoanode for dye-sensitized solar cell (DSSC) was primarily prepared via a two-step process which involved hydrothermal growth of ZnO nanograss on the fluorine-doped tin oxide (FTO) substrate and subsequently chemisorption of PANI on the surfaces of the ZnO nanorods. The PANI hybridized ZnO nanograss films were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectra (FT-IR), and the results indicated that there were chemical interactions between PANI and ZnO. Both pure ZnO nanograss and PANI hybridized ZnO nanograss were applied to DSSC. The results of photoelectrochemical measurement showed that the photocurrent density of PANI (100 mg/L) hybridized ZnO nanograss photoanode was significantly enhanced, and the overall light-conversion efficiency increased by 60%. The electrochemical impedance spectra (EIS) displayed that the electron densities in photoanodes of PANI hybridized ZnO nanograss were larger than that in pure ZnO nanograss. This is ascribed to more effective charge separation and faster interfacial charge transferring occurred in the hybrid photoanode.

Very-short-term wind power prediction by a hybrid model with single- and multi-step approaches

NASA Astrophysics Data System (ADS)

Mohammed, E.; Wang, S.; Yu, J.

2017-05-01

Very-short-term wind power prediction (VSTWPP) has played an essential role for the operation of electric power systems. This paper aims at improving and applying a hybrid method of VSTWPP based on historical data. The hybrid method is combined by multiple linear regressions and least square (MLR&LS), which is intended for reducing prediction errors. The predicted values are obtained through two sub-processes:1) transform the time-series data of actual wind power into the power ratio, and then predict the power ratio;2) use the predicted power ratio to predict the wind power. Besides, the proposed method can include two prediction approaches: single-step prediction (SSP) and multi-step prediction (MSP). WPP is tested comparatively by auto-regressive moving average (ARMA) model from the predicted values and errors. The validity of the proposed hybrid method is confirmed in terms of error analysis by using probability density function (PDF), mean absolute percent error (MAPE) and means square error (MSE). Meanwhile, comparison of the correlation coefficients between the actual values and the predicted values for different prediction times and window has confirmed that MSP approach by using the hybrid model is the most accurate while comparing to SSP approach and ARMA. The MLR&LS is accurate and promising for solving problems in WPP.

Hybrid neural network for density limit disruption prediction and avoidance on J-TEXT tokamak

NASA Astrophysics Data System (ADS)

Zheng, W.; Hu, F. R.; Zhang, M.; Chen, Z. Y.; Zhao, X. Q.; Wang, X. L.; Shi, P.; Zhang, X. L.; Zhang, X. Q.; Zhou, Y. N.; Wei, Y. N.; Pan, Y.; J-TEXT team

2018-05-01

Increasing the plasma density is one of the key methods in achieving an efficient fusion reaction. High-density operation is one of the hot topics in tokamak plasmas. Density limit disruptions remain an important issue for safe operation. An effective density limit disruption prediction and avoidance system is the key to avoid density limit disruptions for long pulse steady state operations. An artificial neural network has been developed for the prediction of density limit disruptions on the J-TEXT tokamak. The neural network has been improved from a simple multi-layer design to a hybrid two-stage structure. The first stage is a custom network which uses time series diagnostics as inputs to predict plasma density, and the second stage is a three-layer feedforward neural network to predict the probability of density limit disruptions. It is found that hybrid neural network structure, combined with radiation profile information as an input can significantly improve the prediction performance, especially the average warning time ({{T}warn} ). In particular, the {{T}warn} is eight times better than that in previous work (Wang et al 2016 Plasma Phys. Control. Fusion 58 055014) (from 5 ms to 40 ms). The success rate for density limit disruptive shots is above 90%, while, the false alarm rate for other shots is below 10%. Based on the density limit disruption prediction system and the real-time density feedback control system, the on-line density limit disruption avoidance system has been implemented on the J-TEXT tokamak.

Understanding band gaps of solids in generalized Kohn-Sham theory.

PubMed

Perdew, John P; Yang, Weitao; Burke, Kieron; Yang, Zenghui; Gross, Eberhard K U; Scheffler, Matthias; Scuseria, Gustavo E; Henderson, Thomas M; Zhang, Igor Ying; Ruzsinszky, Adrienn; Peng, Haowei; Sun, Jianwei; Trushin, Egor; Görling, Andreas

2017-03-14

The fundamental energy gap of a periodic solid distinguishes insulators from metals and characterizes low-energy single-electron excitations. However, the gap in the band structure of the exact multiplicative Kohn-Sham (KS) potential substantially underestimates the fundamental gap, a major limitation of KS density-functional theory. Here, we give a simple proof of a theorem: In generalized KS theory (GKS), the band gap of an extended system equals the fundamental gap for the approximate functional if the GKS potential operator is continuous and the density change is delocalized when an electron or hole is added. Our theorem explains how GKS band gaps from metageneralized gradient approximations (meta-GGAs) and hybrid functionals can be more realistic than those from GGAs or even from the exact KS potential. The theorem also follows from earlier work. The band edges in the GKS one-electron spectrum are also related to measurable energies. A linear chain of hydrogen molecules, solid aluminum arsenide, and solid argon provide numerical illustrations.

Understanding band gaps of solids in generalized Kohn–Sham theory

PubMed Central

Perdew, John P.; Yang, Weitao; Burke, Kieron; Yang, Zenghui; Gross, Eberhard K. U.; Scheffler, Matthias; Scuseria, Gustavo E.; Henderson, Thomas M.; Zhang, Igor Ying; Ruzsinszky, Adrienn; Peng, Haowei; Sun, Jianwei; Trushin, Egor; Görling, Andreas

2017-01-01

The fundamental energy gap of a periodic solid distinguishes insulators from metals and characterizes low-energy single-electron excitations. However, the gap in the band structure of the exact multiplicative Kohn–Sham (KS) potential substantially underestimates the fundamental gap, a major limitation of KS density-functional theory. Here, we give a simple proof of a theorem: In generalized KS theory (GKS), the band gap of an extended system equals the fundamental gap for the approximate functional if the GKS potential operator is continuous and the density change is delocalized when an electron or hole is added. Our theorem explains how GKS band gaps from metageneralized gradient approximations (meta-GGAs) and hybrid functionals can be more realistic than those from GGAs or even from the exact KS potential. The theorem also follows from earlier work. The band edges in the GKS one-electron spectrum are also related to measurable energies. A linear chain of hydrogen molecules, solid aluminum arsenide, and solid argon provide numerical illustrations. PMID:28265085

Band structure calculations of CuAlO2, CuGaO2, CuInO2, and CuCrO2 by screened exchange

NASA Astrophysics Data System (ADS)

Gillen, Roland; Robertson, John

2011-07-01

We report density functional theory band structure calculations on the transparent conducting oxides CuAlO2, CuGaO2, CuInO2, and CuCrO2. The use of the hybrid functional screened-exchange local density approximation (sX-LDA) leads to considerably improved electronic properties compared to standard LDA and generalized gradient approximation (GGA) approaches. We show that the resulting electronic band gaps compare well with experimental values and previous quasiparticle calculations, and show the correct trends with respect to the atomic number of the cation (Al, Ga, In). The resulting energetic depths of Cu d and O p levels and the valence-band widths are considerable improvements compared to LDA and GGA and are in good agreement with available x-ray photoelectron spectroscopy data. Lastly, we show the calculated imaginary part of the dielectric function for all four systems.

Deep donor state of the copper acceptor as a source of green luminescence in ZnO

NASA Astrophysics Data System (ADS)

Lyons, J. L.; Alkauskas, A.; Janotti, A.; Van de Walle, C. G.

2017-07-01

Copper impurities have long been linked with green luminescence (GL) in ZnO. Copper is known to introduce an acceptor level close to the conduction band of ZnO, and the GL has conventionally been attributed to transitions involving an excited state which localizes holes on neighboring oxygen atoms. To date, a theoretical description of the optical properties of such deep centers has been difficult to achieve due to the limitations of functionals in the density functional theory. Here, we employ a screened hybrid density functional to calculate the properties of Cu in ZnO. In agreement with the experiment, we find that CuZn features an acceptor level near the conduction band of ZnO. However, we find that CuZn also gives rise to a deep donor level 0.46 eV above the valence band of ZnO; the calculated optical transitions involving this state agree well with the GL observed in ZnO:Cu.

High density harp or wire scanner for particle beam diagnostics

DOEpatents

Fritsche, C.T.; Krogh, M.L.

1996-05-21

Disclosed is a diagnostic detector head harp used to detect and characterize high energy particle beams using an array of closely spaced detector wires, typically carbon wires, spaced less than 0.1 cm (0.040 inch) connected to a hybrid microcircuit formed on a ceramic substrate. A method to fabricate harps to obtain carbon wire spacing and density not previously available utilizing hybrid microcircuit technology. The hybrid microcircuit disposed on the ceramic substrate connects electrically between the detector wires and diagnostic equipment which analyzes pulses generated in the detector wires by the high energy particle beams. 6 figs.

Light-controlled plasmon switching using hybrid metal-semiconductor nanostructures.

PubMed

Paudel, Hari P; Leuenberger, Michael N

2012-06-13

We present a proof of concept for the dynamic control over the plasmon resonance frequencies in a hybrid metal-semiconductor nanoshell structure with Ag core and TiO(2) coating. Our method relies on the temporary change of the dielectric function ε of TiO(2) achieved through temporarily generated electron-hole pairs by means of a pump laser pulse. This change in ε leads to a blue shift of the Ag surface plasmon frequency. We choose TiO(2) as the environment of the Ag core because the band gap energy of TiO(2) is larger than the Ag surface plasmon energy of our nanoparticles, which allows the surface plasmon being excited without generating electron-hole pairs in the environment at the same time. We calculate the magnitude of the plasmon resonance shift as a function of electron-hole pair density and obtain shifts up to 126 nm at wavelengths around 460 nm. Using our results, we develop the model of a light-controlled surface plasmon polariton switch.

Carbon Nanotube Nanoelectrode Array for Ultrasensitive DNA Detection

NASA Technical Reports Server (NTRS)

Li, Jun; Koehne, Jessica; Chen, Hua; Cassell, Alan; Ng, Hou Tee; Fan, Wendy; Ye, Qi; Han, Jie; Meyyappan, M.

2003-01-01

A reliable nanoelectrode array based on vertically aligned multi-walled carbon nanotubes (MWNTs) embedded in SiO2 is used for ultrasensitive DNA detection. Characteristic nanoelectrode behavior is observed using low-density MWNT arrays for measuring both bulk and surface immobilized redox species such as K4Fe(CN)6. The open-end of MWNTs present similar properties as graphite edge-plane electrodes with wide potential window, flexible chemical functionalities, and good biocompatibility. Oligonucleotide probes are selectively functionalized at the open ends cf the nanotube array and specifically hybridized with oligonucleotide targets. The guanine groups are employed as the signal moieties in the electrochemical measurements. Ru(bpy)3(2+) mediator is used to further amplify the guanine oxidation signal. The hybridization of subattomoles of PCR amplified DNA targets is detected electrochemically by combining the MWNT nanoelectrode array with the Ru(bpy)32' amplification mechanism. This system provides a general platform of molecular diagnostics for applications requiring ultrahigh sensitivity, high-degree of miniaturization, and simple sample preparations.

Design of defect spins in piezoelectric aluminum nitride for solid-state hybrid quantum technologies

DOE PAGES

Seo, Hosung; Govoni, Marco; Galli, Giulia

2016-02-15

Spin defects in wide-band gap semiconductors are promising systems for the realization of quantum bits, or qubits, in solid-state environments. To date, defect qubits have only been realized in materials with strong covalent bonds. Here, we introduce a strain-driven scheme to rationally design defect spins in functional ionic crystals, which may operate as potential qubits. In particular, using a combination of state-of-the-art ab-initio calculations based on hybrid density functional and many-body perturbation theory, we predicted that the negatively charged nitrogen vacancy center in piezoelectric aluminum nitride exhibits spin-triplet ground states under realistic uni- and bi-axial strain conditions; such states maymore » be harnessed for the realization of qubits. As a result, the strain-driven strategy adopted here can be readily extended to a wide range of point defects in other wide-band gap semiconductors, paving the way to controlling the spin properties of defects in ionic systems for potential spintronic technologies.« less

Surface interaction of H2S, SO2, and SO3 on fullerene-like gallium nitride (GaN) nanostructure semiconductor

NASA Astrophysics Data System (ADS)

Salimifard, M.; Rad, A. Shokuhi; Mahanpoor, K.

2017-10-01

Density functional theory (DFT) using MPW1PW91 and B3LYP hybrid functionals was utilized for quantum-based investigations of three major sulfur compounds (H2S, SO2, and SO3) adsorption onto fullerene-like Ga12N12 nanocluster. All chemicals showed high chemisorption with the order of SO3>SO2>>H2S. Results of charge analysis showed that during adsorption, transfer of charge is from H2S to nanocluster while reverse direction of charge transfer is found for SO2 and SO3 molecules. Partial dissociation is found for adsorbates especially for SO2 and SO3 molecules. Results of thermochemistry analysis show negative values for enthalpy and Gibbs free energy of adsorption, confirming exothermic spontaneous process. Analysis of frontier molecular orbital (FMO) showed important role of orbital hybridizing towards formation of new bonds upon adsorption. As a result, we introduce Ga12N12 nanocluster as a strong adsorbent for sulfur compounds.

Hydrogen and dihydrogen bonding of transition metal hydrides

NASA Astrophysics Data System (ADS)

Jacobsen, Heiko

2008-04-01

Intermolecular interactions between a prototypical transition metal hydride WH(CO) 2NO(PH 3) 2 and a small proton donor H 2O have been studied using DFT methodology. The hydride, nitrosyl and carbonyl ligand have been considered as site of protonation. Further, DFT-D calculations in which empirical corrections for the dispersion energy are included, have been carried out. A variety of pure and hybrid density functionals (BP86, PW91, PBE, BLYP, OLYP, B3LYP, B1PW91, PBE0, X3LYP) have been considered, and our calculations indicate the PBE functional and its hybrid variation are well suited for the calculation of transition metal hydride hydrogen and dihydrogen bonding. Dispersive interactions make up for a sizeable portion of the intermolecular interaction, and amount to 20-30% of the bond energy and to 30-40% of the bond enthalpy. An energy decomposition analysis reveals that the H⋯H bond of transition metal hydrides contains both covalent and electrostatic contributions.

Synthesis of immunotargeted magneto-plasmonic nanoclusters.

PubMed

Wu, Chun-Hsien; Sokolov, Konstantin

2014-08-22

Magnetic and plasmonic properties combined in a single nanoparticle provide a synergy that is advantageous in a number of biomedical applications including contrast enhancement in novel magnetomotive imaging modalities, simultaneous capture and detection of circulating tumor cells (CTCs), and multimodal molecular imaging combined with photothermal therapy of cancer cells. These applications have stimulated significant interest in development of protocols for synthesis of magneto-plasmonic nanoparticles with optical absorbance in the near-infrared (NIR) region and a strong magnetic moment. Here, we present a novel protocol for synthesis of such hybrid nanoparticles that is based on an oil-in-water microemulsion method. The unique feature of the protocol described herein is synthesis of magneto-plasmonic nanoparticles of various sizes from primary blocks which also have magneto-plasmonic characteristics. This approach yields nanoparticles with a high density of magnetic and plasmonic functionalities which are uniformly distributed throughout the nanoparticle volume. The hybrid nanoparticles can be easily functionalized by attaching antibodies through the Fc moiety leaving the Fab portion that is responsible for antigen binding available for targeting.

Keyhole behavior and liquid flow in molten pool during laser-arc hybrid welding

NASA Astrophysics Data System (ADS)

Naito, Yasuaki; Katayama, Seiji; Matsunawa, Akira

2003-03-01

Hybrid welding was carried out on Type 304 stainless steel plate under various conditions using YAG laser combined with TIG arc. During arc and laser-arc hybrid welding, arc voltage variation was measured, and arc plasma, laser-induced plume and evaporation spots as well as keyhole behavior and liquid flow in the molten pool were observed through CCD camera and X-ray real-time transmission apparatus. It was consequently found that hybrid welding possessed many features in comparison with YAG laser welding. The deepest weld bead could be produced when the YAG laser beam of high power density was shot on the molten pool made beforehand stably with TIG arc. A keyhole was long and narrow, and its behavior was rather stable inside the molten pool. It was also confirmed that porosity was reduced by the suppression of bubble formation in hybrid welding utilizing a laser of a moderate power density.

Accurate critical pressures for structural phase transitions of group IV, III-V, and II-VI compounds from the SCAN density functional

NASA Astrophysics Data System (ADS)

Shahi, Chandra; Sun, Jianwei; Perdew, John P.

2018-03-01

Most of the group IV, III-V, and II-VI compounds crystallize in semiconductor structures under ambient conditions. Upon application of pressure, they undergo structural phase transitions to more closely packed structures, sometimes metallic phases. We have performed density functional calculations using projector augmented wave (PAW) pseudopotentials to determine the transition pressures for these transitions within the local density approximation (LDA), the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA), and the strongly constrained and appropriately normed (SCAN) meta-GGA. LDA underestimates the transition pressure for most of the studied materials. PBE under- or overestimates in many cases. SCAN typically corrects the errors of LDA and PBE for the transition pressure. The accuracy of SCAN is comparable to that of computationally expensive methods like the hybrid functional HSE06, the random phase approximation (RPA), and quantum Monte Carlo (QMC), in cases where calculations with these methods have been reported, but at a more modest computational cost. The improvement from LDA to PBE to SCAN is especially clearcut and dramatic for covalent semiconductor-metal transitions, as for Si and Ge, where it reflects the increasing relative stabilization of the covalent semiconducting phases under increasing functional sophistication.

Agent-based power sharing scheme for active hybrid power sources

NASA Astrophysics Data System (ADS)

Jiang, Zhenhua

The active hybridization technique provides an effective approach to combining the best properties of a heterogeneous set of power sources to achieve higher energy density, power density and fuel efficiency. Active hybrid power sources can be used to power hybrid electric vehicles with selected combinations of internal combustion engines, fuel cells, batteries, and/or supercapacitors. They can be deployed in all-electric ships to build a distributed electric power system. They can also be used in a bulk power system to construct an autonomous distributed energy system. An important aspect in designing an active hybrid power source is to find a suitable control strategy that can manage the active power sharing and take advantage of the inherent scalability and robustness benefits of the hybrid system. This paper presents an agent-based power sharing scheme for active hybrid power sources. To demonstrate the effectiveness of the proposed agent-based power sharing scheme, simulation studies are performed for a hybrid power source that can be used in a solar car as the main propulsion power module. Simulation results clearly indicate that the agent-based control framework is effective to coordinate the various energy sources and manage the power/voltage profiles.

A high energy and power sodium-ion hybrid capacitor based on nitrogen-doped hollow carbon nanowires anode

NASA Astrophysics Data System (ADS)

Li, Dongdong; Ye, Chao; Chen, Xinzhi; Wang, Suqing; Wang, Haihui

2018-04-01

The sodium ion hybrid capacitor (SHC) has been attracting much attention. However, the SHC's power density is significantly confined to a low level due to the sluggish ion diffusion in the anode. Herein, we propose to use an electrode with a high double layer capacitance as the anode in the SHC instead of insertion anodes. To this aim, nitrogen doped hollow carbon nanowires (N-HCNWs) with a high specific surface area are prepared, and the high capacitive contribution during the sodium ion storage process is confirmed by a series of electrochemical measurements. A new SHC consisting of a N-HCNW anode and a commercial active carbon (AC) cathode is fabricated for the first time. Due to the hybrid charge storage mechanism combining ion insertion and capacitive process, the as-fabricated SHC strikes a balance between the energy density and power density, a energy density of 108 Wh kg-1 and a power density of 9 kW kg-1 can be achieved, which overwhelms the electrochemical performances of most reported AC-based SHCs.

Modeling plasma-assisted growth of graphene-carbon nanotube hybrid

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

Tewari, Aarti

2016-08-15

A theoretical model describing the growth of graphene-CNT hybrid in a plasma medium is presented. Using the model, the growth of carbon nanotube (CNT) on a catalyst particle and thereafter the growth of the graphene on the CNT is studied under the purview of plasma sheath and number density kinetics of different plasma species. It is found that the plasma parameter such as ion density; gas ratios and process parameter such as source power affect the CNT and graphene dimensions. The variation in growth rates of graphene and CNT under different plasma power, gas ratios, and ion densities is analyzed.more » Based on the results obtained, it can be concluded that higher hydrocarbon ion densities and gas ratios of hydrocarbon to hydrogen favor the growth of taller CNTs and graphene, respectively. In addition, the CNT tip radius reduces with hydrogen ion density and higher plasma power favors graphene with lesser thickness. The present study can help in better understanding of the graphene-CNT hybrid growth in a plasma medium.« less

Thermodynamics and vibrational study of hydrogenated carbon nanotubes: A DFT study

NASA Astrophysics Data System (ADS)

Khalil, Rana M. Arif; Hussain, Fayyaz; Rana, Anwar Manzoor; Imran, Muhammad

2018-02-01

Thermodynamic stability of the hydrogenated carbon nanotubes has been explored in the chemisorption limit. Statistical physics and density functional theory calculations have been used to predict hydrogen release temperatures at standard pressure in zigzag and armchair carbon nanotubes. It is found that hydrogen release temperatures decrease with increase in diameters of hydrogenated zigzag carbon nanotubes (CNTs) but opposite trend is noted in armchair CNTs at standard pressure of 1 bar. The smaller diameter hydrogenated zigzag CNTs have large values of hydrogen release temperature due to the stability of Csbnd H bonds. The vibrational density of states for hydrogenated carbon nanotubes have been calculated to confirm the Csbnd H stretching mode caused by sp3 hybridization.

How to compute isomerization energies of organic molecules with quantum chemical methods.

PubMed

Grimme, Stefan; Steinmetz, Marc; Korth, Martin

2007-03-16

The reaction energies for 34 typical organic isomerizations including oxygen and nitrogen heteroatoms are investigated with modern quantum chemical methods that have the perspective of also being applicable to large systems. The experimental reaction enthalpies are corrected for vibrational and thermal effects, and the thus derived "experimental" reaction energies are compared to corresponding theoretical data. A series of standard AO basis sets in combination with second-order perturbation theory (MP2, SCS-MP2), conventional density functionals (e.g., PBE, TPSS, B3-LYP, MPW1K, BMK), and new perturbative functionals (B2-PLYP, mPW2-PLYP) are tested. In three cases, obvious errors of the experimental values could be detected, and accurate coupled-cluster [CCSD(T)] reference values have been used instead. It is found that only triple-zeta quality AO basis sets provide results close enough to the basis set limit and that sets like the popular 6-31G(d) should be avoided in accurate work. Augmentation of small basis sets with diffuse functions has a notable effect in B3-LYP calculations that is attributed to intramolecular basis set superposition error and covers basic deficiencies of the functional. The new methods based on perturbation theory (SCS-MP2, X2-PLYP) are found to be clearly superior to many other approaches; that is, they provide mean absolute deviations of less than 1.2 kcal mol-1 and only a few (<10%) outliers. The best performance in the group of conventional functionals is found for the highly parametrized BMK hybrid meta-GGA. Contrary to accepted opinion, hybrid density functionals offer no real advantage over simple GGAs. For reasonably large AO basis sets, results of poor quality are obtained with the popular B3-LYP functional that cannot be recommended for thermochemical applications in organic chemistry. The results of this study are complementary to often used benchmarks based on atomization energies and should guide chemists in their search for accurate and efficient computational thermochemistry methods.

Experimental investigation of adiabatic compression and heating using collision of an MHD-driven jet with a gas target cloud for magnetized target fusion

NASA Astrophysics Data System (ADS)

Seo, Byonghoon; Li, Hui; Bellan, Paul

2017-10-01

We are studying magnetized target fusion using an experimental method where an imploding liner compressing a plasma is simulated by a high-speed MHD-driven plasma jet colliding with a gas target cloud. This has the advantage of being non-destructive so orders of magnitude more shots are possible. Since the actual density and temperature are much more modest than fusion-relevant values, the goal is to determine the scaling of the increase in density and temperature when an actual experimental plasma is adiabatically compressed. Two new-developed diagnostics are operating and providing data. The first new diagnostic is a fiber-coupled interferometer which measures line-integrated electron density not only as a function of time, but also as a function of position along the jet. The second new diagnostic is laser Thomson scattering which measures electron density and temperature at the location where the jet collides with the cloud. These diagnostics show that when the jet collides with a target cloud the jet slows down substantially and both the electron density and temperature increase. The experimental measurements are being compared with 3D MHD and hybrid kinetic numerical simulations that model the actual experimental geometry.

The onset of calcium carbonate nucleation: a density functional theory molecular dynamics and hybrid microsolvation/continuum study.

PubMed

Di Tommaso, Devis; de Leeuw, Nora H

2008-06-12

Density functional theory (Perdew-Burke-Ernzerhof) based methods have been used to study the structure and hydration environment of the building blocks of CaCO 3 in aqueous solutions of calcium bicarbonate and calcium carbonate. Car-Parrinello molecular dynamics simulations of Ca(2+)/CO3(2-) and Ca (2+)/HCO3(-) in explicit water were performed to investigate the formation of CaCO3 and the hydration shell of the solvated hetero-ion pair. Our simulations show that the formation of the monomer of CaCO3 occurs with an associative mechanism and that the dominant building block of calcium (bi)carbonate in aqueous solution is Ca[eta(1)-(H)CO3](H2O)5, i.e., the preferred hydration number is five, while the (bi)carbonate is coordinated to the calcium in a monodentate mode. This result agrees with static calculations, where a hybrid approach using a combination of explicit solvent molecules and a polarizable continuum model has been applied to compute the solvation free energies of calcium bicarbonate species. Furthermore, the discrete-continuum calculations predict that the Ca(HCO3)2 and Ca(HCO3)3(-) species are stable in an aqueous environment preferentially as Ca(HCO3)2(H2O)4 and Ca(HCO3)3(H2O)2(-), respectively.