Electronic-energy-structure calculations of silicon and silicon dioxide using the extended tight-binding method

We have studied the electronic energy structure of silicon and silicon dioxide using the extended tight-binding method. For silicon, we found that the basis set in terms of single Gaussian-type orbitals is able to reproduce the band structure which is in good agreement with the experimental data. However, simple linear combination of atomic orbitals failed to describe the band order of the lower conduction bands. For silicon dioxide, we calculated the energy band, total and orbital densities of states of $\beta$-cristobalite. In terms of these, we obtained a consistent interpretation of various experimental measurements on amorphous silicon dioxide. Furthermore, by examining the orbital character and the calculated charge densities of various states, we determined the origin of the bonding in silicon dioxide.