The surface and bulk excitons of crystalline LiF. Li +nF −m cluster embedded in an ionic cage

Abstract

The bulk and surface excitons in the crystalline LiF were theoretically studied by means of a cluster model embedded in the ion cage. The method employed is that of the self-consistent field (SCF) theory, where multi-center exchange potentials as well as integrals are calculated exactly within the accuracy of the basis sets. It will be shown that the bulk exciton band lies 11.3 eV above the valence band at the SCF level approximation while a correlation correction brings the band 13.4 eV above the valence band. The experimental bulk value is 13.5 eV. The SCF approximation gives the surface exciton 9.4 eV above the valence band while the correlation correction brings the band 11.5 eV above. The experimental value is 10.3 eV. The difference of the charge distributions between the surface and bulk exciton states will be also discussed.