Computational Study of Structural Transformation in Densified Silica glass

Abstract

Pressure-induced change in structure and properties of noncrystalline materials, such as liquids and glasses, is an important and challenging issue in condensed-matter physics. In this study, molecular dynamics (MD) was used to provide insight into the microscopic picture of changes in the structural correlation of densified SiO₂ glass. The simulations are based on the effective interatomic potential. Changes in the position and height of the first sharp peak in the pair distribution function and bond-angle distributions were investigated as a function of density. The pair-distribution function show that the average Si-O bond length at normal density is 1.62 Å, then linearly increases to 1.67 Å at high density. At high density where the glass reaches the stishovite density the Si-O coordination changes from 4 to 5.8 and the O-Si-O angle distribution is peaked at 90^o with a full width at half maximum (FWHM) of 21^o and the Si-O-Si angle distribution is peaked at 95^o and 128^o. The Si-O bond angle distribution becomes covalent-like and the O-Si-O bond angle distribution becomes broader upon densification. These results provide firm evidence that the system has transformed from a corner-sharing tetrahedral network to one in which there are corner-sharing and edge-sharing octahedral.