Abstract: Quantitative relation of local structure, optical spectra and electron paramagnetic resonance (EPR) spectra of NiF₂ crystal is estiblished. A semi-SCF d-orbit wave functions model for free Ni²⁺ ions, a point-charge-dipole model and a μ-k-α correlation ligand-field model for Ni²⁺ -6X^-(X=F, Cl, Br, I) clusters are used. Zero-field splitting (ZFS) D, E and paramagnetic g-factor are calculated by complete diagonalization procedures (CDP) and high-order perturbation formulas. The results show that:(a) D and E errors calculated by high-order perturbation formulas are larger; (b) D and E calculated by CDP, optical spectra and the g-factor, are in good agreement with those of experiments.

Key words: crystal and ligand fields, complete diagonalization procedure (CDP), high-order perturbation, optical spectra, electron paramagnetie resonance (EPR)spectra