Comparative Ab initio calculations for ABO ₃ perovskite (001), (011) and (111) as well as YAlO ₃ (001) surfaces and F centers

By means of the hybrid exchange-correlation functionals, we performed predictive ab initio calculations for industrially most important ABO ₃ perovskites, like, BaTiO ₃ , SrTiO ₃ , CaTiO ₃ , SrZrO ₃ and PbZrO ₃ (001), (011) and (111) surfaces as well as bulk and (001) surface F-centers. From another side we performed comparative ab initio calculations for charged and polar YAlO ₃ (001) surfaces. For BaTiO ₃ , CaTiO ₃ , SrZrO ₃ and PbZrO ₃ perovskite neutral (001) surfaces, in most cases, all upper surface layer atoms relax inwards, whereas all second surface layer atoms relax upwards, and again, all third surface layer atoms relax inwards. The atom relaxation pattern for YAlO ₃ polar and charged (001) surfaces is completely different from the ABO ₃ perovskite neutral (001) surfaces. The ABO ₃ perovskite (001) surface energies are practically equal for both AO and BO ₂ -terminations, and they are considerably smaller than (011) and especially (111) polar and charged surface energies. The atomic displacement magnitudes of nearest neighbor atoms around the (001) surface F-center in ABO ₃ perovskites are considerably larger than the related displacement magnitudes of nearest neighbor atoms around the bulk F-center. In the ABO ₃ perovskites the electron charge is considerably better localized inside the bulk F-center than in the (001) surface F-center, where the oxygen vacancy charge is more delocalized over the nearest neighbor atoms than in the bulk Fcenter case. The (001) surface F-center formation energy in the ABO ₃ perovskites is smaller than the bulk F-center formation energy, which triggers the F-center segregation from the ABO ₃ perovskite bulk towards its (001) surfaces. In most cases the (001) surface F-center induced defect level in the band gap of ABO ₃ perovskites is located closer to the (001) surface conduction band bottom than the bulk F-center induced defect level to the bulk conduction band bottom.