Electronic properties of α-quartz under pressure

The electronic structure of α-quartz is investigated within the local-density formalism using recently developed soft pseudopotentials. We present results for the band structure, density of states, and charge density of α-quartz at ambient pressure and near the crystalline-to-amorphous transition. The results at ambient pressure compare well with experiment, and are generally consistent with earlier theoretical analysis. Pressure is found to induce a strong interaction between the Si-O bonding and O 2p lone-pair valence states. The gap between the corresponding bands vanishes in the region of the transition to the glass phase. The fundamental band gap increases, instead, with increasing pressure. Trends in the pressure dependence of the electronic structure are discussed in connection with the distortion of the oxygen sublattice towards an ideal close-packed configuration.