Approximate Self-Consistent-Field Study of the(NiF6)4−Cluster

Abstract

An approximate Hartree-Fock self-consistent-field (SCF) calculation has been carried out for the ${(\mathrm{N}\mathrm{i}{\mathrm{F}}_{6})}^{4\ensuremath{-}}$ cluster. Exponential-type orbitals with four independent radial functions were employed for the nickel $3d$ electrons, two radial functions for the fluorine $1s$ and $2s$ electrons, and one for the fluorine $2p$ electrons. A core potential was used to represent the metal ($1s\ensuremath{-}3p$) electrons. All one-electron integrals and all one- and two-center two-electron integrals were evaluated. A closed-shell SCF program was used with orbital occupation numbers adjusted to approximate the open shell. The results of comparisons at different stages in the convergence of the SCF iteration show large differences in $10Dq$ and the degree of delocalization. This implies that some of the earlier simplifications of the SCF treatment are not valid; that is, significant ligand ($2s\ensuremath{-}2{p}_{\ensuremath{\sigma}}$) mixing is found and the metal $3d$ functions make an important contribution to the bonding orbitals.