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 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 The Crystal Structure of Rare-Earth Impurity Centers R3+ in MeF2: ab initio Calculation

2019 ◽  
Vol 14 (4) ◽  
pp. 91-102
Author(s):  
V. A. Chernyshev ◽  
A. V. Arkhipov
Keyword(s):  
Crystal Structure ◽  
Rare Earth ◽  
Ab Initio ◽  
Periodic Structures ◽  
Hybrid Functional ◽  
Rare Earth Ion ◽  
Hartree Fock ◽  
Impurity Centers ◽  
Angular Coordinates ◽  
Impurity Ion

Ab initio calculations of the impurity centers R3+ (R = La – Lu) in CaF2 were carried out. The calculations were performed by using hybrid functional which takes into account both local and nonlocal (at the Hartree – Fock formalism) exchange. The crystal structure of impurity centers was investigated. The distance “rare-earth ion – ligand”, the radial and angular coordinates of the ions at several coordination spheres near to the impurity ion are determined. Calculations were carried out in the program CRYSTAL17, designed to simulate periodic structures within the MO LCAO approach.

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 Computational Methods for Ab Initio Molecular Dynamics

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Eric Paquet ◽  
Herna L. Viktor
Keyword(s):  
Molecular Dynamics ◽  
Quantum Mechanics ◽  
Ab Initio ◽  
First Principles ◽  
Density Functional ◽  
Path Integrals ◽  
Ab Initio Molecular Dynamics ◽  
Molecular Systems ◽  
Hartree Fock ◽  
Computational Perspective

Ab initio molecular dynamics is an irreplaceable technique for the realistic simulation of complex molecular systems and processes from first principles. This paper proposes a comprehensive and self-contained review of ab initio molecular dynamics from a computational perspective and from first principles. Quantum mechanics is presented from a molecular dynamics perspective. Various approximations and formulations are proposed, including the Ehrenfest, Born–Oppenheimer, and Hartree–Fock molecular dynamics. Subsequently, the Kohn–Sham formulation of molecular dynamics is introduced as well as the afferent concept of density functional. As a result, Car–Parrinello molecular dynamics is discussed, together with its extension to isothermal and isobaric processes. Car–Parrinello molecular dynamics is then reformulated in terms of path integrals. Finally, some implementation issues are analysed, namely, the pseudopotential, the orbital functional basis, and hybrid molecular dynamics.

Relation between Magnetic, Spectroscopic and Structural Properties of Binuclear Copper(II) Complexes of Pentadentate Schiff-base Ligand, Semi-empirical and ab-initio Calculations

2003 ◽  
Vol 58 (5-6) ◽  
pp. 363-372 ◽  
Author(s):  
Y. Elerman ◽  
H. Kara ◽  
A. Elmali
Keyword(s):  
Ab Initio ◽  
Coupling Constants ◽  
Antiferromagnetic Coupling ◽  
X Ray Diffraction ◽  
Hartree Fock ◽  
Ligand Orbital ◽  
Rhf Calculations ◽  
The Difference ◽  
Semi Empirical

The synthesis and characterization of [Cu2(L1)(3,5 prz)] (L1=1,3-Bis(2-hydroxy-3,5-chlorosalicylideneamino) propan-2-ol) 1 and of [Cu2(L2)(3,5 prz)] (L2=1,3-Bis(2-hydroxy-bromosalicylideneamino) propan-2-ol) 2 are reported. The compounds were studied by elemental analysis, infrared and electronic spectra. The structure of the Cu2(L1)(3,5 prz)] complex was determined by x-ray diffraction. The magnetochemical characteristics of these compounds were determined by temperaturedependent magnetic susceptibility measurements, revealing their antiferromagnetic coupling. The superexchange coupling constants are 210 cm−1 for 1 and 440 cm−1 for 2. The difference in the magnitude of the coupling constants was explained by the metal-ligand orbital overlaps and confirmed by ab-initio restricted Hartree-Fock (RHF) calculations. In order to determine the nature of the frontier orbitals, Extended Hückel Molecular Orbital (EHMO) calculations are also reported.

Structure, Spectroscopic Study and ab initio Calculations on Third-order Nonlinear Optical Behavior of N-(2-Hydroxy-4-methoxybenzylidene)-3- nitroaniline

2008 ◽  
Vol 63 (11) ◽  
pp. 1315-1320
Author(s):  
Hüseyin Üver ◽  
Aslı Karaka§ ◽  
Ayhan Elmalı ◽  
T. Nuri Durlu
Keyword(s):  
Ab Initio ◽  
Nonlinear Optical ◽  
Photon Absorption ◽  
X Ray Diffraction ◽  
Third Order ◽  
Hartree Fock ◽  
H Nmr ◽  
Calculation Results ◽  
Zero Values ◽  
Optical Behavior

Abstract N-(2-hydroxy-4-methoxybenzylidene)-3-nitroaniline (1) has been synthesized and characterized by X-ray diffraction analysis, FTIR and 1H NMR spectroscopy. The maximum one-photon absorption (OPA) wavelengths recorded by quantum mechanical computations using a configuration interaction (CI) method are estimated in the UV region to be shorter than 450 nm, showing good optical transparency to the visible light. We have computed both dispersion-free (static) and also frequency-dependent (dynamic) linear polarizabilities (α) and second hyperpolarizabilities (γ) by using the time-dependent Hartree-Fock (TDHF) method to provide an insight into the microscopic third-order nonlinear optical (NLO) behavior of the title compound. The ab initio calculation results with non-zero values on (hyper)polarizabilities indicate that the synthesized molecule might possess microscopic third-order NLO phenomena.

scholarly journals Vibrationally and Spin-Orbit-Resolved Inner-Shell X-ray Absorption Spectroscopy of the NH+ Molecular Ion: Measurements and ab Initio Calculations

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 67
Author(s):  
Stéphane Carniato ◽  
Jean-Marc Bizau ◽  
Denis Cubaynes ◽  
Eugene T. Kennedy ◽  
Ségolène Guilbaud ◽  
...  
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Theoretical Calculations ◽  
High Sensitivity ◽  
Open Shell ◽  
Field Configuration ◽  
High Spectral Resolution ◽  
Spin Orbit ◽  
Molecular Ion ◽  
Hartree Fock

This article presents N2+ fragment yields following nitrogen K-shell photo-absorption in the NH+ molecular ion measured at the SOLEIL synchrotron radiation facility in the photon energy region 390–450 eV. The combination of the high sensitivity of the merged-beam, multi-analysis ion apparatus (MAIA) with the high spectral resolution of the PLEIADES beamline helped to resolve experimentally vibrational structures of highly excited [N1s−1H]*+ electronic states with closed or open-shell configurations. The assignment of the observed spectral features was achieved with the help of density functional theory (DFT) and post-Hartree Fock Multiconfiguration Self-Consistent-Field/Configuration Interaction (MCSCF/CI) ab-initio theoretical calculations of the N1s core-to-valence and core-to-Rydberg excitations, including vibrational dynamics. New resonances were identified compared to previous work, owing to detailed molecular modeling of the vibrational, spin-orbit coupling and metastable state effects on the spectra. The latter are evidenced by spectral contributions from the 4Σ− electronic state which lies 0.07 eV above the NH+2Π ground state.

SYNTHESIS, CRYSTAL STRUCTURE, SPECTROSCOPIC STUDIES AND AB-INITIO CALCULATIONS ON THIRD-ORDER OPTICAL NONLINEARITY OF A FIVE-COORDINATE CHLOROIRON(III) COMPLEX

2007 ◽  
Vol 16 (03) ◽  
pp. 329-341 ◽  
Author(s):  
ASLI KARAKAS ◽  
EMINE DONMEZ ◽  
HULYA KARA ◽  
AYHAN ELMALI
Keyword(s):  
Ab Initio ◽  
Optical Nonlinearity ◽  
Spectroscopic Studies ◽  
Optical Measurements ◽  
Photon Absorption ◽  
X Ray Diffraction ◽  
Third Order ◽  
Hartree Fock ◽  
Vis Spectroscopy ◽  
Calculation Results

A five-coordinate chloroiron(III) complex has been synthesized and characterized by X-ray diffraction analysis and UV-Vis spectroscopy. The maximum one-photon absorption (OPA) wavelengths recorded by both linear optical measurements and quantum mechanical computations using the configuration interaction (CI) method are estimated to be shorter than 400 nm in the UV region, showing good optical transparency to visible light. To investigate the microscopic third-order nonlinear optical (NLO) behavior of the title compound, we have computed both dispersion-free (static) and also frequency-dependent (dynamic) linear polarizabilities (α) and second hyperpolarizabilities (γ) at λ = 825–1125 nm and 1050–1600 nm wavelength areas using the time-dependent Hartree–Fock (TDHF) method. The ab-initio calculation results with non-zero values on (hyper)polarizabilities indicate that the synthesized molecule might possess microscopic third-order NLO phenomena.

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