Calculations were made of the electronic structures of point defects in reduced rutile by using a semi-empirical self consistent method. Models for both Ti interstitials and O vacancies were reported. In each case, it was found that the donor levels ranged from 0.7 to 0.8eV for isolated defects. The defects had an effective screening radius of less than 0.5nm. Results were also reported for clusters of defects. These suggested that a model in which the screening charges of multiple defects were added would give quite accurate results for systems with multiple defects. A comparison of the present results with infra-red data suggested that defect clustering occurred in almost stoichiometric rutile.

Electronic Structure of Point Defects in Rutile TiO2. Yu, N., Halley, J.W.: Physical Review B, 1995, 51[8], 4768-76