Structural transformation, intermediate-range order, and dynamical behavior of SiO2 glass at high pressures.

Pressure-induced structural transformation in ${\mathrm{SiO}}_{2}$ glass is investigated with molecular dynamics. At high densities, the height of the first sharp diffraction peak is considerably diminished, its position changes from 1.6 to 2.2 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$, and a new peak appears at 2.85 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$. At twice the normal density, the Si-O bond length increases, the Si-O coordination changes from 4 to 6, and the O-Si-O band angle changes from 109\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{}. This is a tetrahedral to octahedral transformation, which was reported recently by Meade, Hemley, and Mao [Phys. Rev. Lett. 69, 1387 (1992)]. Results for phonon density of states also reveal significant changes at high pressures.