Elastic properties of semiconductors studied by extended Hückel theory

For thirty diamond- and zinc-blende-structure semiconductors, the elastic shear constant (${\mathit{c}}_{11}$-${\mathit{c}}_{12}$)/2, polarity ${\mathrm{\alpha }}_{\mathit{p}}$, effective atomic charge ${\mathit{Z}}^{\mathrm{*}}$, transfer parameter β, and transverse charge ${\mathit{e}}_{\mathrm{T}}^{\mathrm{*}}$ are calculated from band-structure calculations based on the extended Hückel tight-binding method. The results are compared with previous theoretical calculations and experiment. It is found that improved agreement with experiment is obtained for (${\mathit{c}}_{11}$-${\mathit{c}}_{12}$)/2 in comparison to a calculation based upon universal tight-binding parameters, which was already in rather good accord. For the effective charges, inclusion of nonorthogonalities in the Hückel theory increases their estimated values considerably and brings them into good agreement with experiment.