First-principles study of crystalline silica

We have investigated the structural properties of five different crystalline forms of ${\mathrm{SiO}}_2$ using a first-principles approach. An ultrasoft Vanderbilt pseudopotential is generated for oxygen which enables us to use a small plane-wave cutoff of 25 Ry. The relative stability, the equation of state, and pressure-dependent structural parameters of all five polymorphs have been calculated and found to be in very good agreement with available experimental results.