Ab-initio Study of structural, elastic, electronic and optical properties of hexahalometallate single crystals K2XBr6(X = Se, Pt)

Some physical properties of hexahalometallate K2XBr6(X = Se, Pt) were computed in the zinc blend structure using GGA-PBESOL. The cell constant of K2SeBr6 and K2PtBr6 is consistent to the experiment value quoted in the literature, where the error is 0.95% and 1%. K2SeBr6 and K2PtBr6 present covalent bonding, high anisotropy and are ductile. The elastic constants of K2SeBr6 and K2PtBr6 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 K2SeBr6 than in K2PtBr6, hence the Coulomb interaction in K2PtBr6 is greater than that of K2SeBr6. The internal coordinate of Br atom in K2PtBr6 is lower than that of the same atom in K2SeBr6, 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 K2SeBr6 and K2PtBr6.