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 analysed. Born effective charges are used as a criterion of correlating these models. It is shown that taking into account gradients of effective electric fields on anions and high electric permittivity ensures the adequate description of polarization in these crystals by using the Slater localized (static) model. The results of our calculations in the framework of the Slater model are given and compared with ab initio calculation data.