ELECTRONIC-PROPERTIES OF CRYSTALLINE AND AMORPHOUS SIO2 INVESTIGATED VIA ALL-ELECTRON CALCULATIONS AND PHOTOEMISSION SPECTROSCOPY

The electronic properties of silicon dioxide at sere pressure are investigated by means of full-potential linearized augmented-plane-wave calculations and of x-ray and ultraviolet photoemission spectroscopies. The comparison between our theoretical and experimental results regarding the valence band structure of cu-quarts (the crystalline polymorph of silica stable at normal conditions) shows that the main features at lower binding energies (mainly the O 2p bonding and nonbonding states) are well reproduced, while the binding energy of the O 2s semicore states is underestimated by theory, due to local-density approximation. In addition, photoemission measurements on amorphous SiO2 show that the overall structure of the valence band is very similar to that of the ordered phase. Nevertheless, some minor features are observed in ru-quartz spectra, due to long-range order of the crystalline structure.