Exchange and correlation effects in transition-metal oxides 3dn (n = 4, 5 and 6)

In order to clarify the competition of exchange and correlation energies vs crystal-field stabilisation energy, a simple approach is proposed. The exchange and correlation contributions are described on the base of Brandow and Kanamori’s U, U′ and J_H parameters. The dependence of the crystal field effect on site distortion has simply been modelled using a linear interpolation between undistorted and fully distorted sites. This approach leads to establish phase diagrams for d⁴, d⁵ and d⁶ cations, allowing us to predict the spin-state stability range depending on exchange (J_H), crystal field (Dq) and distortion (k) parameters. It can be used to complement the Extended Hückel Tight Binding calculations of the electronic structure of materials having a noticeable ionic character such as 3d transition-metal oxides, in order to interpret the electronic behaviour, and, particularly, discuss the insulating-vs-metallic character of these oxides. To cite this article: M. Pouchard et al., C. R. Chimie 6 (2003) 000–000.