Core polarization contributions to hyperfine effects of paramagnetic centers in ionic crystals

Abstract

The theory for exchange core polarization in hyperfine interactions is formulated using the moment perturbation method for the case when the original basis functions are not orthogonal. Such a situation is typical of a wide variety of paramagnetic systems in the solid state, such as color centers and iron group ions in ionic crystals. The procedure consists of collecting terms proportional to μ N in the total energy, including both one- and two-electron operators in the total Hamiltonian. After some manipulation, the core polarization contribution is shown to have the same form as for the orthogonal case with the valence orbital orthogonalized to the unperturbed core wavefunctions. We have applied our analysis to an example, namely the F-center in LiF. A positive contribution from the core polarization was found for both the isotropic and anisotropic hyperfine constants of the nearest neighbor Li + ions adding to the direct effects from overlap in both cases.