ELECTRONIC-PROPERTIES OF ALPHA-QUARTZ UNDER HIGH-PRESSURE AND THE TRANSITION TO THE AMORPHOUS PHASE

The electronic properties of a-quartz, at ambient pressure and in conn ection with the structural deformation induced by compression, are exa mined via first-principles calculations, based on the full-potential l inearized augmented-plane-wave method. A detailed analysis of the dens ity of states and of the charge density as a function of pressure is p resented. The results at ambient pressure are in good agreement with e xperiments and earlier theoretical studies. We found that the forbidde n energy range between Si-O bonding and O 2p nonbonding states vanishe s in the region of the transition to the amorphous phase, indicating a strong hybridization between these states. This hybridization turns o ut to be more compatible with a different Si coordination and may lead , by local rearrangement, to the formation of a mixed phase. The funda mental band gap is found to increase with pressure.