Density of States and Group Velocity Calculations for SiO2

Ab initio calculations of the electron group velocity for SiO₂ are worked out. The conduction bands are calculated by means of two different techniques: Hartree-Fock (HF) and Density-Functional Theory (DFT). Eight energy bands have been used to calculate the density of states and group velocity for the energies of interest. Two different crystal structures of SiO2, built-up by the same fundamental unit, namely, the SiO₄ tetrahedron, are investigated: they are the a-quartz, and the ß-cristobalite.Fig. 3: GV vs. energy for a-quartz and ß-cristobalite. Solid lines: HF; dashed lines: DFT; circles: parabolic-band approximation.