First-principles calculations of the electronic structure of fluorite-typecrystals (CaF2, BaF2, SrF2, and PbF2) containing Frenkel defects. Analysisof optical and transport properties

The electronic structure of the alkali-earth fluorides CaF2, BaF2, SrF2, an d PbF2 with Frenkel defects is investigated in the tight-binding approximat ion by the LMTO method. The defect formation and migration energies are cal culated. The electronic structure and optical excitations of a H center in a defective fluorite structure are examined. It is shown on the basis of ca lculations of the binding energies that CaF2, BaF2, and SrF2 are ionic comp ounds, while the chemical bond in PbF2 is partially covalent. Possible meth ods of displacement of interstitial fluorine atoms that lead to the observe d optical spectra of an H center are investigated. (C) 1998 American Instit ute of Physics. [S1063-7834(98)01211-8].