scholarly journals Фотонный спектр Eu-=SUB=-2-=/SUB=-Sn-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-: ab initio расчет

2020 ◽  
Vol 128 (11) ◽  
pp. 1668
Author(s):  
В.А. Чернышев ◽  
П.А. Агзамова ◽  
А.В. Архипов
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Vibrational Mode ◽  
Periodic Structures ◽  
Hybrid Functional ◽  
Fundamental Vibration ◽  
Functional Theory ◽  
Hartree Fock ◽  
Displacement Vectors ◽  
Lcao Approximation

Crystal structure and phonon spectrum of crystal Eu2Sn2O7 were studied within the framework of density functional theory and MO LCAO approach. The calculations were performed by using hybrid functional that takes into account both local and nonlocal (in the Hartree–Fock formalism) exchange. The calculations were performed in the CRYSTAL17 program intended for simulating periodic structures in the MO LCAO approximation. The fundamental vibration frequencies of Eu2Sn2O7 were calculated. The frequencies, intensities and types of the Raman and the IR-active modes have been calculated. An analysis of the displacement vectors obtained from the ab initio calculation, made it possible to estimate the degree of the ion participation in the vibrational mode. The elastic constants of the crystal have been calculated too.

scholarly journals Cтруктура и динамика решетки кристаллов Nd-=SUB=-2-=/SUB=-TiO-=SUB=-5-=/SUB=- и Sm-=SUB=-2-=/SUB=-TiO-=SUB=-5-=/SUB=-: ab initio расчет

2019 ◽  
Vol 61 (6) ◽  
pp. 1151
Author(s):  
В.А. Чернышев ◽  
В.С. Рюмшин
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Vibration Frequencies ◽  
Hybrid Functional ◽  
Fundamental Vibration ◽  
Functional Theory ◽  
Lattice Constants ◽  
Hartree Fock ◽  
Phonon Spectra ◽  
First Time

Crystal structure and phonon spectra R2TiO5 (R = Nd, Sm) were studied within the framework of density functional theory and MO LKAO approach. The calculations were performed by using hybrid functional that takes into account both local and nonlocal (at the Hartree-Fock formalism) exchange. The coordinates of the ions in the unit cell and the lattice constants are calculated. The fundamental vibration frequencies of R2TiO5 (R = Nd, Sm) were calculated. The relative intensities of the Raman lines and the intensity of the IR-active modes have been calculated. The elastic constants of the crystal have been calculated at the first time.

Structural and Vibrational Properties of Crystals with a Rare-Earth Sublattice: Ab Initio Calculations

2018 ◽  
Vol 271 ◽  
pp. 85-91
Author(s):  
Vladislav P. Petrov ◽  
Vladimir A. Chernyshev ◽  
Anatoly E. Nikiforov
Keyword(s):  
Rare Earth ◽  
Ab Initio ◽  
Density Functional ◽  
Periodic Structures ◽  
X Ray Diffraction ◽  
Rare Earth Ion ◽  
Hartree Fock ◽  
Lcao Approximation ◽  
Local Contribution ◽  
Non Local

We investigated the crystal structure, vibrational and elastic properties of crystals with a rare-earth sublattice related to different structural types at ab initio level of modeling: elpasolite Cs2NaRF6 −> pyrochlore R2Ti2O7 −> ferroborate RFe3(BO3)4, where R is a rare-earth ion or yttrium. The calculations were performed in the framework of a density functional theory using the hybrid functionals containing local and non-local contribution (i.e. Hartree-Fock exchange term) to the exchange energy. We used CRYSTAL program for simulating periodic structures in the MO LCAO approximation. To describe the internal shell of a rare-earth ion up to 4f, we used the nonrelativistic pseudopotential («4f-in-core») that describes the effect of internal electrons on the outer valence shells. The results of the calculations are in good agreement with the available experimental data of IR and Raman experiments, X-ray diffraction analysis for the rows of elpasolites, pyrochlores and ferroborates.

scholarly journals Фононный спектр La-=SUB=-2-=/SUB=-Zr-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-: ab initio расчет

2019 ◽  
Vol 127 (11) ◽  
pp. 758
Author(s):  
В.А. Чернышев
Keyword(s):  
Crystal Structure ◽  
Density Functional Theory ◽  
Elastic Constants ◽  
Phonon Spectrum ◽  
Density Functional ◽  
Periodic Structures ◽  
Functional Theory ◽  
Hartree Fock ◽  
Lcao Approximation ◽  
Hybrid Functionals

Crystal structure and phonon spectrum of La2Zr2O7 were studied within the framework of density functional theory and MO LKAO approach. The calculations were performed by using hybrid functionals that takes into account both local and nonlocal (in the Hartree–Fock formalism) exchange. The frequencies, types, and intensities of Raman and IR modes are determined. The elastic constants have been calculated too. The calculations were performed in the CRYSTAL17 program intended for simulating periodic structures in the MO LCAO approximation.

Polaronic and Bipolaronic Enhancement of Second Hyperpolarizabilities in Dithienyl Polyenes from Ab Initio Quantum Methods

1999 ◽  
Vol 597 ◽  
Author(s):  
Steven Trohalaki ◽  
Robert J. Zellmer ◽  
Ruth Pachter
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Valence Bond ◽  
Closed Shell ◽  
Functional Theory ◽  
Molecular Conformations ◽  
Hartree Fock ◽  
Molecular Charge ◽  
Field Methodology ◽  
Moller Plesset

AbstractSpangler and He [1,2] have shown that dithienyl polyenes form extremely stable bipolaronic dications when oxidatively doped in solution. Previous theoretical studies applied empirical methods to predict bipolaronic enhancement of hyperpolarizabilities for simple polyenes [3,4]. Here, we employ density functional theory to optimize the gas-phase molecular conformations of neutral, cationic, and dicationic forms of a series of dithienyl polyenes, where the number of ethene units, N, is varied from 1–5. Ab initio Hartree-Fock, generalized valence bond, configuration interaction, and Møller-Plesset calculations demonstrate that the dications are farily well described with a closed shell and therefore have little biradicaloid character. Second hyperpolarizabilities, γ, are subsequently calculated using ab initio Hartree-Fock theory and a finite field methodology. As expected, γ increases with the number of ethene units for a given molecular charge. The cations also show the largest increase in γ with N. For a given value of N, the cations display the largest γ values. However, if we treat the dication as a triplet, which might be present in solution, then it displays the largest γ.

scholarly journals Density functional tight binding: values of semi-empirical methods in an ab initio era

2014 ◽  
Vol 16 (28) ◽  
pp. 14368-14377 ◽  
Author(s):  
Qiang Cui ◽  
Marcus Elstner
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Density Functional ◽  
Tight Binding ◽  
Empirical Methods ◽  
Functional Theory ◽  
Hartree Fock ◽  
Semi Empirical

Semi-empirical (SE) methods are derived from Hartree–Fock (HF) or Density Functional Theory (DFT) by neglect and approximation of electronic integrals.

Ab initio Correlation Effects in Density Functional Theories: An Electron-Distribution-Based Study for Neon

2005 ◽  
Vol 70 (8) ◽  
pp. 1157-1176 ◽  
Author(s):  
Karol Jankowski ◽  
Ireneusz Grabowski ◽  
Krzysztof Nowakowski ◽  
Jan Wasilewski
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Physical Nature ◽  
Correlation Effects ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Hartree Fock ◽  
Brueckner Orbitals ◽  
Local Gradient ◽  
The Impact

We have briefly reviewed the idea of studies aiming at such a bridging of the methodological gap between ab initio methods (or wave function theory (WFT)) and density functional theory (DFT) that would afford carrying over results concerning details of the structure of correlation effects from one method to the other. Special attention is paid to the problem of coverage of the WFT correlation effects by the exchange-correlation functionals of DFT. A short survey of the concept of supplementing energy-based investigations in this field by electron-density-based studies is given and illustrated by results for the Ne atom. DFT densities are generated for representatives of all four generations of presently used exchange-correlation functionals, including the recently developed orbital-dependent one. These densities are compared with WFT densities calculated at the MP2, MP3, and Brueckner determinant levels. It is found that the exchange-only parts of the local, gradient-corrected, and hybrid functionals account for the bulk of WFT correlation effects. The impact of the associated correlation functionals is very small and their physical nature is not quite clear. The situation is different for the orbital-dependent functional for which the exchange-only functional provides an almost exact description of the Hartree-Fock density. Here, the correlation effects are entirely represented by the correlation functional. Attention is also paid to the suitability of Kohn-Sham orbitals for the description of WFT correlation effects and to their presumptive similarity with Brueckner orbitals.

scholarly journals Ab initio and first principles theoretical investigations of triplet–triplet fluorescence in trimethylenemethane biradicals

RSC Advances ◽  
2016 ◽  
Vol 6 (87) ◽  
pp. 83668-83672 ◽  
Author(s):  
Yasunori Matsui ◽  
Kosuke Usui ◽  
Hiroshi Ikeda ◽  
Stephan Irle
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
First Principles ◽  
Density Functional ◽  
Theoretical Studies ◽  
Functional Theory ◽  
Hartree Fock ◽  
Theoretical Investigations

Theoretical studies on triplet–triplet (T1 → T0) fluorescence of the arylated trimethylenemethane (TMM) biradicals, 32˙˙, were carried out using post-Hartree–Fock ab initio and various first principles density functional theory methods.

Sign in / Sign up

Export Citation Format

Share Document