Classical molecular dynamical simulations of high pressure behavior of alpha cristobalite (SiO₂)

Abstract

Static and dynamic high pressure experiments reveal that the behavior of α-cristobalite (SiO₂) depends on the rate and the nature of stress loading. To understand this behavior we have carried out extensive molecular dynamics simulations. The response to rapid and simultaneous increase of the pressures and temperatures to the expected Hugoniot values was calculated. These simulations along the simulated Hugoniot path revealed that alpha cristobalite transforms to a new six coordinated phase beyond 16 GPa, 1410.3 K. We find that between 16 and 18 GPa, even after equilibrating for a very long time, the disorder in the stishovite-like phase persists. On release of pressure, this disordered state is retained, in agreement with the experimental observations. Simulations under slow pressure increase show that the observation of Cmcm is sensitive to pressure steps and that stishovite phase arises through the Cmcm phase.