Computer modeling of point defects in perovskite crystals

The results of calculations for mixed perovskite KNb x Ta 1 - x O 3 (KTN) solid solutions are presented and discussed. The semiempirical method of the intermediate neglect of differential overlap (INDO) based on the Hartree-Fock formalism predicts magnitudes of the Nb off-center displacements which are in agreement with EXAFS data. Results are compared with ab initio FP-LMTO first-principles calculations. The latter formalism and the semiempirical INDO methods are combined for the study of hole and electron polarons in perovskites. We calculated the defect migration energies using INDO method and classical shell model (SM) for the cubic phase of the KNbO 3 . The migration energies for the O vacancy obtained by these methods are reasonably close and agree with the only experimental estimate available of 1 eV.