A SELF CONSISTENT ATOMIC DEFORMATION MODEL FOR TOTAL ENERGY CALCULATIONS: APPLICATION TO FERROELECTRICS

An ab initio model for total energy calculations is introduced in which site localized charge densities are determined from the electronic structure of atoms (or ions) in a self consistent overlap potential. In the lowest order expression of the overlap potential the ions are spherical. In this simplest form, polarization can result either from ion displacements or from transfer of charge from one ion to another. Calculations for BaTiO3 and KNbO3 show charge transfer from the O(2p) to the transition metal d states, beginning near the equilibrium volume and increasing with increasing volume. Results are obtained which indicate the transfer effect will be greatly enhanced for transition metal ions on a surface.