The results of electronic structure calculations for various terminations of SrTiO3 (100) and (110) perovskite thin films were considered. The calculations were based upon the ab initio Hartree-Fock method and density functional theory. The results were compared with previous ab initio plane-wave LDA and classical shell model calculations. A considerable calculated increase in the Ti-O chemical bond covalency near to the surface was confirmed by experimental data. Quantum-chemical calculations, performed by using the intermediate neglect of differential overlap method, confirmed the existence of self-trapped electrons in KNbO3, KTaO3 and BaTiO3 crystals. The corresponding lattice relaxation energies were 0.21, 0.27 and 0.24eV, and the optical absorption energies were 0.78, 0.75 and 0.69eV, respectively. The so-called green luminescence (2.2 to 2.3eV) in ABO3 perovskite crystals was attributed to the recombination of electrons and holes forming the charge-transfer vibronic exciton. The calculated luminescence energies for SrTiO3, BaTiO3, KNbO3 and KTaO3 perovskite crystals were in a good agreement with experimentally observed energies.

Modeling of Defects and Surfaces in Perovskite Ferroelectrics. G.Borstel, R.I.Eglitis, E.A.Kotomin, E.Heifets: Physica Status Solidi B, 2003, 236[2], 253-64