O-vacancies at the ii, iii and iv sites. The resulting vacancy formation energies are essentially identical to those obtained for isolated O-vacancies on these sites, with differences of at most 0.10 eV (Figure ). Hence, also in this case the presence of neighboring O-vacancies does not significantly ease the formation of O-vacancies in deeper layers. Plotting the O-vacancy formation energy vs. the charge transfer upon O-vacancy formation (blue symbols, Figure ),