Abstract
A microscopic theory of lattice dynamics of the ionic crystals is developed in the self‐consistent Hartree‐Fock approximation. The work is based on a splitting of the dynamical matrix into two parts, a rigid ion and a polarization part. For ionic crystals such a splitting is especially convenient, because here the rigid ion contribution represents the dominant contribution to the total dynamical matrix. In the theory presented, this part results from the classical Coulomb interaction of the cores and electrons among themselves and with each other within the Heitler‐London approximation. It is obtained without using perturbation theory, therefore no excited states are involved. For a special choice of the localized wave functions the energy expression of Löwdin [23] and Lundqvist [24] is obtained which describes the perturbation of the electron density during a lattice mode by a rigid displacement of localized electron densities including exchange effects. The polarization part takes into account virtual electronic transitions caused by a weak driving electron‐ion potential additively to the rigid ion part. This part is determined by a variational method.