Étude de premier principe des propriétés structurales, mécaniques et électroniques des composés BaX(X=S, Se, Te, Po)

Abstract

A theoretical studies of structural electronic elastic and high pressure properties in barium chalcogenides BaX ( X=S , Se , Te , Po ) are performed using the Full-potential augmented plane wave plus local orbital method (FP-LAPW) .In this approach the local –density approximation (LDA) and generalized gradient approximation (GGA) are used for the exchange –correlation (XC) potential . Moreover, the alternative from of the GGA proposed by Engel and Vosko (GGA-EV) is also used for band structure calculations. The equilibrium lattice constant and the bulk modulus agree well with the experiment. The pressures at which these compounds undergo structural phase transition from NaCl (B1) to CsCl (B2) phase were found to be in good agreement with the available experimental data. Results obtained for band structure using GGA-EV show a significant improvement over other theoretical work and are closer to the experimental data. A linear relationship is observed between theoretical band gap and 1/a2 (where a is lattice constant). We have determined the elastic constants C11, C12 and C44 at ambient condition in both B1 and B2 structures, which have been established neither experimentally nor theoretically. Further, we have also calculated the pressure dependence of the elastic constants for the B1structure of the four compounds.