Role of covalence and of correlation in the dielectric polarization of oxides

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Abstract
The dynamical charges measure the macroscopic polarization induced by a relative sublattice displacement in a polar insulator. When the material has a mixed ionic/covalent character such charges present nontrivial features. Apparently similar oxides have strikingly different behaviors: some (like the ferroelectric perovskites) have giant dynamical charges, while others (like ZnO) are quite normal and display dynamical charges close to the nominal static ones. The rationale for such differences is found, upon closely scrutinizing the covalence mechanism. Furthermore, the effects of electron-electron interaction on the polarization of a model highly correlated dielectric are discussed.