A new approach for calculating the electronic structure and vibrational properties of non-crystalline solids: Effective charges for infrared-active normal mode vibrations in oxide and chalcogenide materials

Abstract This paper applies ab initio calculations to small clusters with short range bonding order for oxide and chalcogenide dielectrics that form continuous random networks (CRN), including, respectively, SiO 2 and GeO 2 , and As 2 S 3 and GeS 2 . The calculations have been used to determine the dependence of the total energy on the bond-angle at the twofold coordinated O- and S-atom sites, and the infrared effective charges of the normal mode network vibrations associated with symmetry determined asymmetric bond-stretching, symmetric bond-stretching (bending) and out-of-plane bond rocking displacements, including decomposition of effective charges in equilibrium distribution, and dynamic charge redistribution components. The results of these calculations are in very good to excellent agreement with experiment. The approach is extended to silicates and their chalcogenide analogs in which pseudo-binary alloy formation causes a disruption of the CRN hosts through formation of ionic bonding arrangements of the metal atoms. This is accompanied by increases in the coordination of O-, S-, Se- and As-atoms of the respective oxide and chalcogenide host CRNs, including SiO 2 and As 2 Se 3 , and leads to a breakdown of 8− N bonding coordination.