Self-consistent-field study of the cluster model in ionic salts. I. NiF₆^4-

Self-consistent-field calculations have been carried out on the NiF ₆^4- cluster in a near-Hartree-Fock basis (for the valence electrons) of Gaussian functions to test the validity of the model for describing the localized properties of ionic salts. Both the spin-restricted and spin-polarized treatments are compared for ground and excited states of the complex ion. From comparison with experimentally obtained results it is concluded that a Hartree-Fock description of the cluster gives reasonably good wavefunctions and energies. Surprisingly, the crystal-field splitting parameter obtained using just the ground-state wavefunction is too large by a factor of 3.