First principle calculations of dielectric and effective charge tensors in barium titanate

Abstract Using Variational Density Functional Perturbation Theory, the dielectric and effective charge tensors of cubic Barium Titanate have been calculated as second derivatives of the total energy with respect to electric field and phonon perturbations. We found a dielectric constant εoo=5.60 and the following effective charges: Z*Ba=2.70; Z*Ti= 7.10; Z*O//= -5.56; Z*O1= -2.12. An estimation of the spontaneous polarisation in the distorted phases is also presented.