The dynamic ionic charge of zincblende type crystals

The ionic charges of zincblende type crystals are discussed. Since the static ionic charges are, in general, quite small in these crystals, the magnitudes of the dynamic ionic charge, e*T, are attributed largely to the effects of charge redistribution. The fairly sizeable values of e*T in Se and Te trigonal crystals must, in fact, be attributed entirely to charge redistribution effects since their static ionic charges are identically zero. Efforts to account for the e*T values in ZnS type crystals using either the shell model or the deformation dipole model have not been too successful. It is urged that theorists turn their attention to ab initio energy-band calculations of long wavelength dynamical properties of zincblende and diamond type crystals, namely: the first-order electric moment (infrared) tensor, ∂M/∂uT; the first-order electric susceptibility (Raman) tensor, ∂χ0/∂uT; and the change in the electric susceptibility with interatomic distance (piezo-optic) tensor, ∂χ0/∂∂.