A systematic study was made of O vacancy formation, on the TiO2 (110) surface, by means of plane-wave pseudopotential density-functional theory calculations. Models were used with a mean number of vacancies per surface unit cell of 0.25 or 0.5. The study comprised several kinds of vacancy within the outermost layers of the surface. It was found that the presence of bridging vacancies was energetically favored, in accord with experimental data, although the formation of sub-bridging vacancies was possible at moderate temperatures. The spin state of the vacancy had little effect upon the results. The atomic displacements were also analyzed and were found to depend strongly upon the particular arrangement of vacancies.

Oxygen Vacancies on TiO2 (110) from First-Principles Calculations. Oviedo, J., San Miguel, M.A., Sanz, J.F.: The Journal of Chemical Physics, 2004, 121[15], 7427-33