Crystal Field Splitting in Correlated Systems with Negative Charge-transfer Gap

Abstract

Special features of the crystal field splitting of d-levels in the transition metal compounds with small or negative charge-transfer gaps ΔCT are considered. We show that in this case the Coulomb term and the covalent contribution to the t2geg splitting have different signs. In order to check theoretical predictions we carried out abinitio band structure calculations for Cs2Au2Cl 6, in which the charge-transfer gap is negative, so that the d-electrons predominantly occupy low-lying bonding states. For these states the eg-levels lie below the t2g ones, which demonstrates that at least in this case the influence of the pd covalency on the total value of the crystal field splitting is stronger than the Coulomb interaction (which would lead to the opposite level order). We also show that the states in the conduction band are made predominantly of p-states of ligands (Cl), with a small admixture of d-states of Au. © 2011 IOP Publishing Ltd.