Quasiparticle excitation energies for the F-center defect in LiCl.

Abstract

The electronic excitation energies of an [ital F]-center defect in a LiCl crystal are calculated in the [ital GW] quasiparticle approximation. The halogen vacancy constituting the [ital F] center is modeled in a supercell geometry that includes equilibrium lattice relaxation corrections to the defect energies. The dynamically screened Coulomb interaction, used in constructing the quasiparticle self-energy, is taken in the generalized plasmon-pole approximation using a model for the static dielectric screening. Excitations from the bound 1[ital s] state to conduction band critical points at [ital X], [ital L], and along [Lambda] are calculated to have energies of 5.7, 4.5, and 5.0 eV, respectively, compared to experimental absorption peaks at 5.8, 4.5, and 5.0 eV. The lowest energy, intradefect level excitation shows the effect of an electron-hole interaction that is not explicitly included in the single-particle [ital GW] self-energy. This contribution is approximated, yielding a calculated energy for the fundamental absorption band of 3.4 eV, as compared to experimental observations of 3.1--3.3 eV.