Density functional modeling of structural and electronic properties of amorphous high temperature oxides

Ab initio molecular dynamics modeling in the NPT ensemble is used to obtain amorphous states by melting SiO ₂, ZrO ₂ and HfO ₂ crystals. A wide range of melt stabilization temperatures are used. Two types of SiO ₂ amorphous states are obtained. For melt temperatures below 4500 K, a perfect silica glass is obtained without any point defects. For melt temperatures above 4500 K, silica point defects such as threefold coordinated oxygen atoms, edge-sharing SiO 4 -tetrahedra, and others together with a wide range of Si-O-Si rings including 3-, and 4-membered rings appear. When the temperature of the melt exceeds the ZrO ₂ and HfO ₂ crystal melting point by 100 – 400 K, a sharp drop in the density of amorphous states is observed, accompanied by a decrease in atomic coordination, but this does not lead to the formation of defect states in the depth of the band gap of hafnium and zirconium dioxides.