Quasiparticle band structure and optical spectrum of CaF2

We present the quasiparticle band structure and optical excitation spectrum of bulk CaF2 using first-principles methods. The quasiparticle band structure is evaluated in Hedin's GW approximation [Phys. Rev. 139, A796 (1965)]. Thereafter, the electron-hole interaction is calculated and the Bethe-Salpeter equation is solved, yielding the optical-absorption spectrum. Particular attention is paid to the Ca 3d states, which contribute to the lower conduction bands, and to the Ca 3s and 3p semicore states, which are included in the GW method as valence states. The calculated quasiparticle band gap is 11.5 eV, which is in agreement with experiment (11.8 eV) and greatly improves the local-density approximation result (6.85 eV). The calculated optical-absorption spectrum and reflectivity spectrum, which consist of an exciton peak at 10.7 eV and several resonant-exciton peaks between 12 and 16 eV, are in good agreement with experiment.