A. Bouhemadou

FP-APW+lo calculations of the electronic and optical properties of alkali metal sulfides under pressure

The electronic and optical properties of M(2)S (M = Li, Na, K andxa0Rb) compounds in the cubic antifluorite structure have been calculated, using a full relativistic version of the full-potential augmented plane-wave plus local orbitals method based on density functional theory, within both the local density approximation (LDA) and the generalized gradient approximation (GGA). Moreover, the Engel-Vosko GGA formalism (EV-GGA) is applied so as to optimize the corresponding potential for band structure calculations. The calculated equilibrium lattices and bulk moduli are in good agreement with the available data. Band structure, density of states, electron charge density and pressure coefficients of energy gaps are given. Results obtained for band structure using EV-GGA are larger than those with LDA and GGA. It is found that the spin-orbit coupling lifts the triple degeneracy at the Γ point and the double degeneracy at the X point. The analysis of the electron charge density shows that the M-S bonds have a significant ionic character. The complex dielectric functions ε(2)(ω) for alkali metal sulfides were calculated for radiation up to 30xa0eV and the assignment of the critical points to the band structure energy differences at various points of the Brillouin zone was made. The pressure and volume dependence of the static dielectric constant and the refractive index are calculated.

Elastic, electronic and optical properties of the filled tetrahedral semiconductor LiCdP

The elastic, electronic and optical properties of the filled tetrahedral semiconductor LiCdP have been investigated using the pseudo-potential plane wave method within the local density functional theory. A numerical first-principles calculation of the elastic constants was used to calculate C11, C12 and C44. The values of the sound velocities in different directions have been calculated. We derived the bulk and shear moduli, Young modulus and Poissons ratio for ideal polycrystalline LiCdP. We estimated the Debye temperature of LiCdP from the average sound velocity. Band structures show that LiCdP is a direct band gap. The density of states and Mulliken charge populations analysis show that the Cd?P bond is typically covalent with a strong hybridization as well as that the Li?P bond has a significant ionic character. The variation of the gap versus pressure is well fitted to a quadratic function and a direct to an indirect band gap transition occurs at 6.80 GPa. Furthermore, the dielectric function, optical reflectivity, refractive index, extinction coefficient and electron energy loss are calculated for radiation up to 20 eV. The results are compared with the available theoretical and experimental data.

First-principle calculations to investigate the elastic and thermodynamic properties of RBRh3 (R = Sc, Y and La) perovskite compounds

We have performed first-principle calculations using the full-potential linear augmented plane wave (FP-LAPW) method within density functional theory (DFT) to investigate the structural, elastic and thermodynamic properties of the cubic perovskite RBRh3 (Ru2009=u2009Sc, Y and La) compounds. The exchange-correlation potential is treated within the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE). Single-crystal elastic constants are calculated using the total energy variation versus strain technique, then the shear modulus, Youngs modulus, Poissons ratio and anisotropic factor are derived for polycrystalline RBRh3 using the Voigt–Reuss–Hill approximations. Analysis of the calculated elastic constants and B/G ratios shows that these compounds are mechanically stable and ductile in nature. Using the quasi-harmonic Debye model, the effect of pressure P and temperature T on the lattice parameter a 0, bulk modulus B 0, thermal expansion coefficient α, Debye temperature and the heat capacity C v for these compounds are investigated for the first time. The computed structural and elastic constants are in good agreement with the available experimental and theoretical data.