Electron-hole excitations in Mg2Si and Mg2Ge compounds -: art. no. 033202

The recently implemented all-electron GW approximation shows that the conduction band quasiparticle energies of Mg2Si and Mg2Ge compounds are shifted by a constant energy Delta toward higher energies compared to the local-density approximation results whereas the valence bands remain unchanged. Including excitonic effects considerably improves the optical spectra peak positions and their intensities obtained within the random-phase approximation. The calculation predicts a low energy structure that is present in the experimental optical spectrum of Mg2Ge but remains to be observed for Mg2Si.