The origin of differences between anatase and rutile properties was addressed, and it was shown that they could be related to a marked difference in the natures of the electronic levels introduced by bulk oxygen vacancies (VOx) in the two materials. These levels had differing locations in the energy gap and gave rise to differing localizations of the electronic charge in real space; thus indicating that the VOx were important in elucidating the differences in properties of the two phases. The present results, achieved by applying a U-correction to local spin-density generalized gradient approximation methods, also showed the importance of using beyond-LSD methods when investigating metal oxides. Only such methods permitted revelation of the differing natures of the VOx electronic states in the two TiO2 phases.

Ab initio Study of the Electronic States Induced by Oxygen Vacancies in Rutile and Anatase TiO2. Mattioli, G., Filippone, F., Alippi, P., Bonapasta, A.A.: Physical Review B, 2008, 78[24], 241201