The ab initio linear muffin-tin orbital method combined with density functional theory (local approximation) and the semiempirical method of the intermediate neglect of differential overlap (INDO) based on the Hartree-Fock formalism are used for the study of the F centers and the hole polarons in KNbO3 perovskite crystals. We present and discuss results of the calculations for SrTiO3 (0 0 0) Surface relaxation with different terminations (SrO and TiO2) using an ab initio methods based on Hartree-Fock (HF) and density functional theory (DFT) formalisms. We compare our results with previous ab initio and shell model (SM) calculations and LEED experiments. (C) 2002 Elsevier Science B.V. All rights reserved.