First-principles study of point defects in rutileTiO2−x

We report our first-principles results on point defects in $\mathrm{Ti}{\mathrm{O}}_2$ in the rutile phase. Both the oxygen vacancy and titanium interstitial are considered. The size effect of the supercell has been examined and the localized state associated with the oxygen vacancy turns out to be sensitive to the supercell size. We find that the oxygen vacancy does not give rise to a defect level within the energy gap while the titanium interstitial creates a localized state $0.2\mathrm{eV}$ below the conduction edge that can be related to the infrared absorption data. The charge accumulation around the oxygen vacancy is attributed to polarization of valence bands.