Electronic structure of point defects in rutile TiO2

We present results of a computation of the electronic structure of point defects in reduced rutile using a semiempirical self-consistent method. Calculations on models of both titanium interstitials and oxygen vacancies are reported. We find donor levels in the range 0.7-0.8 eV for isolated defects in each case. The defects have an effective screening radius of less than 5. We also report results on clusters of defects. These suggest that a model in which the screening charges of multiple defects are added would be quite accurate for systems with multiple defects. Comparison of our results with infrared experiments suggests the presence of defect clustering in nearly stoichiometric rutile, as proposed earlier on the basis of other experiments.