PRESSURE-DEPENDENCE OF THE STRUCTURAL-PROPERTIES OF ALPHA-QUARTZ NEAR THE AMORPHOUS TRANSITION

Silicon dioxide exists in a number of structures. The lowest-energy structure is that of alpha-quartz. We predict the structural properties of alpha-quartz as a function of pressure via total-energy calculations. The calculations are based on recently developed pseudopotentials constructed within the local-density approximation. In addition, we examine the structural properties of alpha-quartz near an order-disorder transition. Quartz undergoes a gradual transition with pressure from a crystalline to an amorphous state. The driving mechanism for this pressure-induced transition is not well understood. We suggest that highly unfavorable interpolyhedral oxygen-oxygen distances, which occur in alpha-quartz at the transition pressure, play a key role in driving the transition.