Ab initio calculation of the quasiparticle spectrum and excitonic effects in Li2O

We report an ab initio calculation of the binding energies and the nature of the excitonic states in the near-gap absorption spectrum of a real solid, Li2O. We calculate the ground-state properties using density-functional theory together with soft pseudopotentials. Applying Hedin's GW approximation for the self-energy corrections to the band structure, we determine the minimal gap about 1 eV above the measured absorption onset. Finally, we obtain agreement with experiment by solving an effective two-particle Schrodinger equation for the electron-hole pairs.