First-principles determination of the sublinear dependence of the direct &) on hydrostatic pressure

The dependence of the direct gap of germanium (${\Gamma }_{25\mathcal{’}}$→${\Gamma }_{2\mathcal{’}}$) on hydrostatic pressure has been calculated from first principles within local-density-functional formalism. This dependence is found to be sublinear. Although the correct gap cannot be obtained within the local-density-functional formalism its pressure dependence is still well accounted for. The linear pressure coefficient ${\mathrm{dE}}_0$/dp obtained for the gap is very well reproduced. The dependence of $E_0$ on the relative change of lattice constant (Δscra/${\mathrm{scra}}_0$) is shown to be supralinear.