Effective Charge Associated with a Displaced Ion in the Orthogonalized-Plane-Wave Formalism

Abstract

The effective-ion-charge concept of Pick and Sarma is examined with respect to the calculation of phonon frequencies of metals. It is shown that the extra charge associated with an ion because of the orthogonalization of the plane waves to the core states is cancelled by a term which results from the nonorthogonality of the single orthogonalized plane waves when the ions are displaced from their equilibrium positions.