Excited States of Transition Metal Oxides

Abstract

A discussion of the electronic structure of the non-metallic transition metal oxides is presented. To be successful any model must quantitatively, at least, describe the following phenomena: insulating behavior of open shell systems; magnetic properties and low lying magnetic excitations; cohesion and phonon spectroscopy; “localized” excitations or excitons and; Bloch like excitations. We argue that the least sophisticated model which can attempt such a description is the Unrestricted Hartree-Fock model (UHF), and even in this limit Koopman’s theorem may not be assumed but rather total energy differences of several self-consistent solutions are needed. We further show that if quantitative accuracy is needed correlation corrections beyond the UHF limit are necessary. We discuss several simple models for inclusion of correlation corrections using techniques of classical electrodynamics on one hand and of Configuration Interaction on the other hand. Detailed calculations are presented using these models and comparisons with optical spectroscopy are made. There is a reasonable comparison of theory and experiment produced by these methods, and the ground state of FeO, CoO and NiO is seen to be insulating whereas that of TiO and VO is seen to be metallic.