Local Density Approximation Total Energy Calculations for Silica and Titania Structure and Defects

Theoretical structural predictions are presented for three polymorphs of silica (α-quartz, α-cristobalite, and stishovite) and the rutile structure of titania. Several defects within the silica system (the oxygen vacancy, a puckering distortion in quartz with no oxygen vacancy, and titanium in silica) are also studied. These ab initio studies are conducted using the local density approximation for electronic structure and total energies and are implemented using some very recent advances in improved pseudopotentials and energy minimization algorithms. Results include two metastable conformations of the oxygen vacancy in silica, similar Si—O and Ti—O bond energies, and equilibrium structures of several defects.