Band-structure calculations of SiO/sub 2/ by means of Hartree-Fock and density-functional techniques

Ab initio calculations of the full-band structure of SiO/sub 2/ are worked out. Both the conduction and valence bands are investigated by means of two different techniques: Hartree-Fock (HF) and density-functional theory (DFT). A number of energy-level diagrams are calculated in order to compare the corresponding density of states in a range of about 10 eV. Different crystal structures of SiO/sub 2/ are studied, that are known to be built-up by the same fundamental unit, namely, the SiO/sub 4/ tetrahedron. All the analyzed systems are polymorphs of silica; specifically, the /spl alpha/- and /spl beta/-quartz, the /spl alpha/- and /spl beta/-cristobalite, and the /spl beta/-tridymite.