Structural properties of α-quartz under high pressure and amorphization effects

The behavior of crystalline {α}-quartz under hydrostatic pressure is studied via total-energy calculations based on the full-potential linearized augmented-plane-wave method, within the local-density approximation. By examining recent experimental data and our theoretical results, the structural properties of {α}-quartz near and above the transition to the amorphous state are determined. Our results indicate that the SiO₄ tetrahedra distort, with a regular and slight decrease of the mean distance Si-O; the interpolyhedral Si-O-Si angles and the O-O distances decrease below the smallest value experimentally observed on ordered silicates, with a dramatic reduction of the structural voids. The oxygen lattice tends towards an ideal close-packed configuration, perhaps highly instable.