Covalent bonding and hybridization effects in the corundum-type transition-metal oxides and

Institut für Physik, Universität Augsburg - 86135 Augsburg, Germany

Corresponding author: volker.eyert@physik.uni-augsburg.de

Received: 6 January 2005
Accepted: 28 April 2005

Abstract

The electronic structure of the corundum-type transition-metal oxides and is studied by means of the augmented spherical wave method, based on density-functional theory and the local density approximation. Comparing the results for the vanadate and the titanate allows us to understand the peculiar shape of the metal density of states, which is present in both compounds. The states are subject to pronounced bonding-antibonding splitting due to metal-metal overlap along the c-axis of the corundum structure. However, the corresponding partial density of states is strongly asymmetric with considerably more weight on the high-energy branch. We argue that this asymmetry is due to an unexpected broadening of the bonding states, which is caused by hybridization with the bands. In contrast, the antibonding states display no such hybridization and form a sharp peak. Our results shed new light on the role of the orbitals for the metal-insulator transitions of . In particular, due to - hybridization, an interpretation in terms of molecular orbital singlet states on the metal-metal pairs along the c-axis is not an adequate description.