Role of tight-binding parameters and scaling laws on effective charges in semiconductors

We compute the transverse effective charges for several compound semiconduc tors by using the empirical tight-binding model and the Berry-phase approac h. We compare different parametrizations showing that a suitable tuning of the scaling laws for the radial part of the hopping parameters provides a f airly good prediction of the effective charges even with the minimal sp(3) basis set. In contrast new and refined parametrizations that reproduce very well the dispersion of the conduction band at equilibrium by including d a nd/or s* polarization orbitals may underestimate the effective charges. We suggest that the root of such a discrepancy may rest with the difficulty of determining the scaling laws for polarization orbital.