Electronic Structure of theFCenter in LiCl

Abstract

The electronic structure of the $F$-center lattice defect in LiCl is investigated with calculations based on the usual model of the $F$ center proposed by de Boer. The ground- and excited-state wave functions and energies of the trapped electron are determined by two different methods. First, the method of linear combination of atomic orbitals (LCAO) is used. This method is capable of yielding good results but the complexity of the necessary calculations is great. In an effort to avoid this complexity the method of vacancy-centered wave functions is investigated. Very simple wave functions are used in this method with satisfactory results. The coefficient of the hyperfine interaction of the $F$-center electron with the nearest-neighbor lithium ion and the oscillator strength of the optical transition are calculated. The distortions of the lattice in the vicinity of the $F$ center are calculated. A very small outward movement of the first and second nearest neighbors occurs in the ground state. The situation in the excited state is complicated by the "$p$-type symmetry of the $F$-electron wave function. In this case, the two nearest-neighbor lithium ions located on the symmetry axis of the wave function are found to undergo a large displacement outward from the vacancy. The other four nearest neighbors displace inward toward the center of the vacancy. The results of the calculations are discussed and detailed comparisons with other work of a similar nature are given.