Hartree-Fock approach to macroscopic polarization:: Dielectric constant and dynamical charges of KNbO3

Within the Hartree-Fock (HF) scheme, we investigate some basic polarization features of the paradigmatic ferroelectric perovskite KNbO3, using a supercell technique. With regard to the spontaneous polarization and the transverse dynamical charge, the HF results are in good agreement with both experiment and density-functional calculations, despite the large difference in the one-electron energy levels calculated with the two methods. On the other hand, the HF value of the electronic dielectric constant a, is substantially lower than experiment, while density-functional values are known to be substantially higher than that.