A new approach to ionic character in solids

If a lattice of point ions is embedded in a free electron gas, the resulting screening can be calculated by first-order perturbation theory. The answer can be expressed in terms of a static wave-number-dependent dielectric function (q). Because the plane-wave approximation gives good results for the valence bandwidths in semiconductors, it is interesting to apply the simple idea of dielectric screening to charge distributions in partially ionic zinc-blende and wurtzite semiconductors. To do so one must include the effect of occupied atomic core states. This is easily done in the effective potential representation. One then finds that dielectric screening gives a good approximation to the results of band calculations for the screening of the longest and strongest Fourier component of the lattice potential. Nonlinear effects leading to the formation of covalent bonds will also be discussed.