LOCALIZED AND DELOCALIZED MODELS IN THE THEORY OF POLARIZATION - PEROVSKITE OXIDES

Possibilities of working out the theory of polarization in perovskite- type oxides in frameworks of localized and delocalized models are anal ysed. Born effective charges are used as a criterion of correlating th ese models. It is shown that taking into account gradients of effectiv e electric fields on anions and high electric permittivity ensures the adequate description of polarization in these crystals by using the S later localized (static) model. The results of our calculations in the framework of the Slater model are given and compared with ab initio c alculation data.