Molecular dynamical calculations of α- quartz implications for shock results

Abstract

We have carried out detailed molecular dynamical calculations as a function of pressure and temperature on SiO₂ with a-quartz as the initial phase. At room temperature, on increase of pressure beyond 21 GPa, we get anisotropic amorphous phase. The glassy phase recovered on release of pressure continues to be compacted and has an average Si-O coordination of about 4.6. The glass becomes isotropic and four coordinated beyond 1000K. The calculated equation of state suggests that the high pressure phase of a-quartz in shock experiments is amorphous with higher coordination of Si and not stishovite. These calculations explain some of the recent experimental results on the shocked recovered phase. The behaviour of pressure induced glass is also calculated and is compared with that of calculated results of fused silica and experiments.