Ab-initio Study of structural, elastic, electronic and optical properties of hexahalometallate single crystals KXBr(X = Se, Pt).

Some physical properties of hexahalometallate KXBr(X = Se, Pt) were computed in the zinc blend structure using GGA-PBESOL. The cell constant of KSeBr and KPtBr is consistent to the experiment value quoted in the literature, where the error is 0.95% and 1%. KSeBr and KPtBr present covalent bonding, high anisotropy and are ductile. The elastic constants of KSeBr and KPtBr are significantly smaller due to their larger reticular distances, lower Coulomb forces and then they are soft and damage tolerant. The interatomic separation is greater in KSeBr than in KPtBr, hence the Coulomb interaction in KPtBr is greater than that of KSeBr. The internal coordinate of Br atom in KPtBr is lower than that of the same atom in KSeBr, and this can be explained by the fact that it is inversely proportional to the atom radius of Se and Pt. There are two major plasmonic processes, with intensities 3.7 and 1.35 located around 53.5 nm and 72.8 nm for KSeBr and KPtBr.