scholarly journals Ab initio теория уравнения состояния сжатых кристаллов инертных газов

2018 ◽  
Vol 60 (1) ◽  
pp. 151
Author(s):  
Е.А. Пилипенко ◽  
Е.П. Троицкая ◽  
Е.Е. Горбенко
Keyword(s):  
Ab Initio ◽  
Short Range ◽  
Equations Of State ◽  
Higher Order ◽  
Quadratic Approximation ◽  
Rare Gas ◽  
Overlap Integral ◽  
Hartree Fock ◽  
Repulsive Potentials ◽  
Three Body

AbstractNonempirical equations of state of compressed rare gas crystals Ne, Ar, Kr, and Xe are studied on the basis of the earlier-obtained ab initio adiabatic potential. The paired and three-body short-range repulsive potentials are calculated by the Hartree–Fock method in the basis of localized functions with their exact mutual orthogonalization and do not contain experimentally determined parameters. The theory is compared with the experiment and results of calculations by other authors. Analysis of the proposed equations of state for large compressions has shown the importance of taking into account the three-body interaction and the terms of the higher order in the overlap integral in compressed neon and the sufficiency of the quadratic approximation in the orthogonalization of functions in heavy rare gas crystals.

Ab Initio Theory of the Equations of State for Light Rare-Gas Crystals

2019 ◽  
pp. 213-229
Author(s):  
Ievgen Ie. Gorbenko ◽  
Elena P. Troitskaya ◽  
Ekaterina A. Pilipenko ◽  
Ilya A. Verbenko ◽  
Yuriy I. Yurasov
Keyword(s):  
Ab Initio ◽  
Equations Of State ◽  
Rare Gas ◽  
Ab Initio Theory

scholarly journals Удельная теплоемкость и температура Дебая сжатого кристаллического неона в модели деформируемых атомов

2020 ◽  
Vol 62 (12) ◽  
pp. 2129
Author(s):  
Е.П. Троицкая ◽  
Е.А. Пилипенко ◽  
Е.Е. Горбенко
Keyword(s):  
Specific Heat ◽  
Ab Initio ◽  
Short Range ◽  
Mean Value ◽  
Face Centered Cubic ◽  
Repulsive Potential ◽  
Body Interaction ◽  
Dynamic Matrix ◽  
Three Body ◽  
Electron Shells

The thermodynamic properties of compressed neon crystal has been theoretically investigated within the ab initio approach taking into account the many-body interaction in the model of deformable atoms. In the short-range repulsive potential, along with the three-body interaction associated with the overlap of the electron shells of atoms, deformation of electron shells of dipole-type atoms is taken into account in the pair and three-particle approximations. The specific heat capacities and the Debye temperature in a wide pressure and temperature range have been calculated using the dynamic matrix constructed with the ab initio short-range repulsive potential and integration over the mean value points of the Chadi–Kohen method. It is shown that the contributions of three-body forces associated with both the overlap of the electron shells of atoms and the deformation of the electron shells increase the value of specific heat of compressed neon face-centered cubic crystals even at zero pressure. The temperature dependences are obtained in good agreement with the available experiment data and calculation results obtained by other researchers.

scholarly journals Абсолютная неустойчивость ГЦК-решетки кристаллов инертных газов под давлением

2019 ◽  
Vol 61 (1) ◽  
pp. 154
Author(s):  
Е.П. Троицкая ◽  
Е.А. Пилипенко ◽  
Е.Е. Горбенко
Keyword(s):  
Short Range ◽  
Elastic Moduli ◽  
Dynamic Instability ◽  
Longitudinal Mode ◽  
Transverse Mode ◽  
Rare Gas ◽  
Short Range Potential ◽  
Fcc Lattice ◽  
Three Body ◽  
Electron Shells

AbstractOn the basis of ab initio calculations of the phonon frequencies of compressed rare-gas crystals in the model of deformable and polarizable atoms, dynamic instability of the fcc lattice of these crystals is studied. In addition to the earlier-considered three-body interaction, which is associated with the overlapping of the electron shells of atoms, the short-range potential includes three-body forces caused by the mutual deformation of the electron shells of neighboring atoms. It is shown that the allowance for the deformation of the dipole-type electron shells of atoms in the pair and three-body approximations leads to softening of the critical vibrations and absolute instability of the fcc lattice at pressures higher than the critical values, p > p _ c . For light crystals of Ne and Ar under compressions of 0.76 ( p _ c = 422 GPa) and 0.71 ( p _ c = 405 GPa), respectively, the softening of the longitudinal mode is observed at the boundary of the Brillouin zone at the point L ; for heavy crystals of Kr and Xe under compressions of 0.686 ( p _ c = 240 GPa) and 0.605 ( p _ c = 88 GPa), the transverse mode T _1 is softened in the direction Σ. The behavior of second-order Fuchs elastic moduli of compressed rare-gas crystals is discussed.

Ab initio Hartree-Fock Investigation of π-Conjugated Compounds Presenting Large βv/βe Ratio: Merocyanines

1998 ◽  
Vol 63 (9) ◽  
pp. 1295-1308 ◽  
Author(s):  
Benoît Champagne ◽  
Thierry Legrand ◽  
Eric A. Perpete ◽  
Olivier Quinet ◽  
Jean-Marie André
Keyword(s):  
Ab Initio ◽  
First Hyperpolarizability ◽  
Conjugated Molecules ◽  
Hartree Fock ◽  
Experimental Discovery ◽  
Conjugated Compounds ◽  
Molecular Frame

CHF/6-311G* calculations of the first electronic and vibrational hyperpolarizabilities reveal that merocyanines present a substantial βv/βe ratio under their quinonoid nonpolar form. It originates from a large vibrational first hyperpolarizability whereas its electronic counterpart is small for this class of push-pull π-conjugated molecules. The transition from the quinonoid to the aromatic configuration is accompanied by an increase of βe and a decrease of the βv/βe ratio as well as by a ≈ 180° rotation in the plane of the molecule of βe and βv with respect to the molecular frame. Our results support the recent experimental discovery that antiparallel aggregation of aromatic and quinonoid forms of merocyanine is energetically favoured and that their first hyperpolarizabilities, which combine constructively, present both electronic and non purely electronic origins.

Modeling of the three-body effects in the Ar[sub 2]O[sup −] trimer from ab initio calculations

2003 ◽  
Vol 118 (6) ◽  
pp. 2731 ◽  
Author(s):  
Jacek Jakowski ◽  
Grzegorz Chałasiński ◽  
S. M. Cybulski ◽  
M. M. Szczȩśniak
Keyword(s):  
Ab Initio Calculations ◽  
Ab Initio ◽  
Three Body

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.

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