Self-Consistent-Field Electronic Excitation Energies for the NiF6−4Cluster Calculated from an Average-of-Configurations State: Reply to a Comment by Peter O'Donnell Offenhartz

The average-of-configuration (AOC) orbital energy difference obtained from linear-combination-of-atomic-orbitals molecular-orbital self-consistent-field (LCAO MO SCF) calculations on octahedral transition-metal clusters does roughly approximate the empirical crystal-field-splitting parameter $10Dq$, as proposed by Offenhartz. With general MO's representing the open $d$ shells, however, a moderate-sized interelectronic repulsion term remains. AOC calculations of Ni${\mathrm{F}}_6^{-4\mathrm{}}$ are presented; they show that this latter term and, thus also, the orbital energy difference depend significantly upon the basis. Accurate treatment of the transition energy therefore requires inclusion of all terms. Certain energy differences among calculated excited states can be fit to the crystal-field-theory scheme as proposed by Wachters, with essentially the same numerical results as he obtained from independent Gaussian-based SCF results for this system.