Investigation of the structural, mechanical, dynamical and thermal properties of CsCaF3 and CsCdF3

The structural, mechanical, dynamical and thermal properties of CsCaF3 and CsCdF3 are presented by using an ab initio pseudopotential method and a linear response scheme, within the generalized gradient approximation. The obtained structural and mechanical properties are in good agreement with other available theoretical and experimental studies. The calculated elastic constants of these materials obey the cubic stability conditions. It has been found that CsCaF3 is brittle whereas CsCdF3 has ductile manner. The full phonon dispersion curves of these materials are reported for the first time in the literature. We have found that calculated phonon modes are positive along the all symmetry directions, indicating that these materials are dynamically stable at the cubic structure. The obtained zone-center phonon modes for CsCaF3 (IR data) are found to be 83 (98) cm(-1), 104 (115) cm(-1), 120 cm(-1), 180 (192) cm(-1), 231 (250.5) cm(-1), 361 (374) cm(-1), 446 (449) cm(-1). Also, we have calculated internal energy, Helmholtz free energy, constant-volume specific heat, entropy and Debye temperature as function of temperature. At the 300 K, specific heats are calculated to be 113.36 J mol(-1) K-1 and 115.58 J mol(-1) K-1 for CsCaF3 and CsCdF3, respectively, which are lower than Doulong-Petit limit (12 472 J mol(-1) K-1)

First-principles study of structural, mechanical, lattice dynamical and thermal properties of nodal-line semimetals ZrXY (X=Si, Ge; Y=S, Se)

The nodal-line semimetals are new and very promising materials for technological applications. To understand their structural, mechanical, lattice dynamical and thermal properties in detail, we have investigated theoretical study of ZrXY (X = Si, Ge; Y = S, Se) using Density Functional Theory for the first time. Obtained lattice parameters are in excellent agreement with previous experimental data. These nodal-line semimetals obey the mechanical stability conditions for tetragonal structure. We obtain Bulk modulus, Shear modulus, Poisson's ratio, Pugh ratio, sound velocities and thermal conductivity using elastic constant. All the materials behave in brittle manner. Poisson's ratio data and Bader charge analysis results indicate that the ionic bonding characters are dominant. Next, the lattice dynamical properties are calculated. Phonon density of states shows that nodal-line semimetals ZrXY are also dynamically stable in the tetragonal structure. Raman and IR active phonon modes are determined. Highest optical mode at gamma point corresponds to A(2u) (IR active) and E-g (Raman active) modes for ZrXSe and ZrXS, respectively. Based on phonon density of states, thermal properties such as Helmholtz free energy, entropy, heat capacity at constant volume and Debye temperature are also presented and discussed

Investigation of structural, mechanical, electronic, optical, and dynamical properties of cubic BaLiF3, BaLiH3, and SrLiH3

The structural, mechanical, electronic, optical, and dynamical properties of BaLiF3, BaLiH3, and SrLiH3 cubic perovskite materials are theoretically investigated by using first principles calculations. Obtained results are in reasonable agreement with other available theoretical and experimental studies. The considered materials are found to be mechanically stable in the cubic structure. We found that all materials are brittle. The modified Becke-Johnson (mBJ) exchange potential has been used here to obtain an accurate band order. The calculated band-gap energy value of BaLiF3 (8.26 eV) within the mBJ potential agrees very well with the experimentally reported value of 8.41 eV. In order to have a deeper understanding of the bonding mechanism and the effect of atomic relaxation on the electronic band structure, the total and partial density of states have also been calculated. We have investigated the fundamental optical properties, such as the real epsilon(1) (omega) and imaginary epsilon(2) (omega) parts of the dielectric function, absorption coefficient alpha(omega), reflectivity R(omega), and refractive index n(omega) in the energy range from 0 to 40 eV within the mBJ potential. The band-gap energy obtained from the absorption spectrum is around 8.76, 3.99, and 3.31 eV for BaLiF3, BaLiH3, and SrLiH3 crystals, respectively. It should be noted that BaLiF3 could be a strong potential candidate as a laser material for the development of a vacuum-ultraviolet light emitting diode once direct transition is confirmed by experimental studies. Finally, we have calculated the lattice dynamical properties of BaLiF3, BaLiH3, SrLiH3, and SrLiF3 crystals. The full phonon dispersion curves of these materials are reported for the first time. Our results clearly indicate that the materials are dynamically stable, except for SrLiF3, in the cubic structure. The obtained zone-center phonon frequencies of BaLiF3, BaLiH3, and SrLiH3 accord very well with previous experimental measurements

AIP Conference Proceedings

We have employed the ab initio pseudopotential method, within a generalized gradient approximation of the density functional theory, a linear response approach, to determine atomic, elastic and lattice dynamical properties of the BaNbO3. The obtained structural and elastic parameter are in good agreement with previous experimental and theoretical results. The analysis of B/G ratio indicates that BaNbO3 is a ductile material. The calculated lattice dynamical properties compared with phonon spectrum of the similar structures

AIP Conference Proceedings

We have presented theoretical investigations of the atomic, elastic and lattice dynamical properties of ScGa3 using an ab-initio pseudopotential method and a linear response scheme, within the generalized gradient approximation. The calculated atomic parameters and elastic constants are in agreement with previous ab initio calculations and experimental measurements. The material shows ductile behavior. Full phonon dispersions for this material are reported

Phonon softening and electron-phonon coupling in the topological nodal-line semimetal ZrGeSe

ZrGeSe is one of the most well-known topological nodal-line semimetals, which possesses linearly dispersive electronic bands near the Fermi surface. However, the lattice-dynamics study and its interaction with the electronic system have not been investigated. We employed the inelastic neutron-scattering method to study the lattice dynamics of ZrGeSe single crystals. The measured acoustic phonon dispersions were compared with lattice-dynamics calculations, with an overall good agreement with theory; however, both the longitudinal and the transverse acoustic phonon dispersions along the (q00) directions demonstrate significant softening, unexpectedly in contrast with the theoretical predictions. Complementary ab initio molecular dynamics simulations indicate an anomalous temperature dependency in the vibrational spectroscopy. We show that strong electron-phonon coupling exists along the Γ-M-X directions and argue that the phonon softening is induced by such electron-phonon coupling