Electronic band structure of stishovite (tetragonal SiO2)

We have calculated the valence-band structure of stishovite, a tetragonal form of Si${\mathrm{O}}_2$, using a simple tight-binding method. As in similar fits to computed valence bands in $\alpha$-quartz and $\beta$-cristobalite, only oxygen orbitals are used in the basis set. Values of the tight-binding parameters are based on the earlier calculations. A direct forbidden optical edge is predicted, as found in other tetragonal oxides of group-IV elements. There is no gap between bonding and nonbonding valence bands, in contrast to forms of Si${\mathrm{O}}_2$ which exhibit twofold oxygen coordination. Implications regarding the electronic structure of $a$-Si${\mathrm{O}}_2$ are discussed.