Density functional theory was used to investigate the formation and properties of O vacancies on the rutile TiO2(110) surface. It was found that formation of the positively charged bridging-O vacancy (BOV+, 4.2eV) was the most favored, followed by the positively charged in-plane-O vacancy (POV+, 4.5eV). In contrast, the formation of the neutral bridging-O and in-plane-O vacancies, and their O vacancies (BOV2+ and POV2+) required much higher energies (7.9 and 8.3 vs. 8.1 and 8.6eV), respectively.

Formation of Oxygen Vacancies on TiO2(110) Surfaces. Wang, S.G., Wen, X.D., Cao, D.B., Li, Y.W., Wang, J., Jiao, H.: Surface Science, 2005, 577[1], 69-76