Theoretical investigation of zero-field splitting and local structure distortion for a substitution of Fe3+ ion in CdCl2 crystal

A theoretical method for studying the inter-relation between electron and molecule structure is proposed on the basis of the complete energy matrices of the electron–electron repulsion, the ligand-field and the spin–orbit coupling for d5d5 configuration ion in a trigonal ligand-field. As an application, the local distortion structure of (FeCl6)3-(FeCl6)3- coordination complex for Fe3+ ions doped into CdCl2 is investigated. Both the second-order zero-field splitting parameter b20 and fourth-order zero-field splitting parameter b40 are considered simultaneously in the structural investigation. By diagonalizing the complete energy matrices, the local structure distortion parameters ΔR=−0.24 Å, Δθ=2.137° at 26 K and ΔR=−0.203 Å, Δθ=2.515° at 225 K for Fe3+ ions in CdCl2 are determined. These results elucidate a microscopic origin of various ligand-field parameters which are usually used empirically for the interpretation of electron paramagnetic resonance results. It is found that the theoretical results are in good agreement with the experimental values.