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.

scholarly journals Three-body correlations in mesonic-atom-like systems

2020 ◽  
Author(s):  
Hajime Moriya ◽  
Wataru Horiuchi ◽  
Jean-Marc Richard
Keyword(s):  
Short Range ◽  
Exotic Atoms ◽  
Short Range Potential ◽  
Range Potential ◽  
Three Body ◽  
Simple Models

Three-body correlations in three-body exotic atoms are studied with simple models that consist of three bosons interacting through a superposition of long- and short-range potentials. We discuss the correlations among particles by comparing the energy shifts given by precise three-body calculations and by the Deser-Trueman formula, in which the long- and short-range contributions are factorized. By varying the coupling of the short-range potential, we evaluate the ranges of the strength where the two-body correlations dominate and where the three-body correlations cannot be neglected.

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.

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 Энергия фононов и нулевых колебаний в сжатых кристаллических инертных газах

2019 ◽  
Vol 61 (10) ◽  
pp. 1890
Author(s):  
Е.П. Троицкая ◽  
Е.А. Пилипенко ◽  
Е.Е. Горбенко
Keyword(s):  
Nearest Neighbor ◽  
Zero Point ◽  
Pair Interaction ◽  
Mean Value ◽  
Rare Gas ◽  
Point Energy ◽  
Dynamic Matrix ◽  
Short Range Repulsion ◽  
Three Body ◽  
Electron Shells

A dynamic matrix of rare-gas crystals is constructed on the basis of a nonempirical short-range repulsion potential taking into account the three-body interaction and dipole-type deformation of the electron shells of atoms in the two- and three-body approximations in the model of deformable and polorizable atoms. Ab initio calculations of the phonon energy for compressed rare-gas crystals were performed at the two and ten mean-value points of the Chadi-Cohen method in a wide pressure range. It is shown that the contribution of three-body forces associated with the overlap of the electron shells of nearest-neighbor atoms in the phonon frequencies is small against the background of pair interaction, even at high pressure and most noticeable in Xe. The contribution of the deformation of the electron shells in the two- and three-body approximations is different for the different mean-value points and increases with increasing pressure. Comparison of the zero-point energy calculated by the Chadi-Cohen method for compressed crystals of the Ne–Xe series was performed with the available experiment at p=0 and the results of other authors.

scholarly journals Supernova constraints on an axion-photon-dark photon interaction

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
Anson Hook ◽  
Gustavo Marques-Tavares ◽  
Clayton Ristow
Keyword(s):  
Longitudinal Mode ◽  
Transverse Mode ◽  
The Other ◽  
Unusual Feature ◽  
Dark Sector ◽  
Longitudinal Modes ◽  
Dark Photon ◽  
Transverse Modes ◽  
Weakly Coupled ◽  
Photon Coupling

Abstract We present the supernova constraints on an axion-photon-dark photon coupling, which can be the leading coupling to dark sector models and can also lead to dramatic changes to axion cosmology. We show that the supernova bound on this coupling has two unusual features. One occurs because the scattering that leads to the trapping regime converts axions and dark photons into each other. Thus, if one of the two new particles is sufficiently massive, both production and scattering become suppressed and the bounds from bulk emission and trapped (area) emission both weaken exponentially and do not intersection The other unusual feature occurs because for light dark photons, longitudinal modes couple more weakly than transverse modes do. Since the longitudinal mode is more weakly coupled, it can still cause excessive cooling even if the transverse mode is trapped. Thus, the supernova constraints for massive dark photons look like two independent supernova bounds super-imposed on top of each other.

DFT study on thermo-elastic properties of Ru2FeZ (Z = Si, Ge, Sn) Heusler alloys

2018 ◽  
Vol 32 (05) ◽  
pp. 1850045 ◽  
Author(s):  
Aneeza Iftikhar ◽  
Afaq Ahmad ◽  
Iftikhar Ahmad ◽  
Muhammad Rizwan
Keyword(s):  
Thermal Stability ◽  
Elastic Properties ◽  
Density Functional ◽  
Heusler Alloys ◽  
Longitudinal Mode ◽  
Transverse Mode ◽  
Functional Theory ◽  
Formation Energies ◽  
Thermal Stability Of ◽  
Temperature Melting

We studied the thermo-elastic properties of Ru2FeZ (Z[Formula: see text]=[Formula: see text]Si, Ge, Sn) Heusler alloys within the framework of density functional theory. Thermo-elastic properties corresponding to elastic modulus, anisotropy, phase stability, elastic wave velocities, thermal stability, Debye temperature, melting temperature, thermal conductivity and formation energy are calculated. The elastic constants C[Formula: see text] predict the structural and dynamical stabilities while the formation energies show thermal stability of the alloys at 0 K. Pugh’s and Poisson’s ratios display the ductile nature of alloys. All alloys are anisotropic and we also observed that Ru2FeSn is the hardest material than Ru2FeSi and Ru2FeGe. Moreover, longitudinal mode of vibrations are also observed and are maximum along [100], [110] and [111] directions than the transverse mode of vibrations.

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