Covalent bonding and hybridization effects in the corundum-type transition-metal oxides V2O3 and Ti2O3

摘要

The electronic structure of the corundum-type transition-metal oxides V2O3and Ti2O3 is studied by means of the augmented spherical wave method, based ondensity-functional theory and the local density approximation. Comparing theresults for the vanadate and the titanate allows us to understand the peculiarshape of the metal 3d a_{1g} density of states, which is present in bothcompounds. The a_{1g} states are subject to pronounced bonding-antibondingsplitting due to metal-metal overlap along the c-axis of the corundumstructure. However, the corresponding partial density of states is stronglyasymmetric with considerably more weight on the high energy branch. We arguethat this asymmetry is due to an unexpected broadening of the bonding a_{1g}states, which is caused by hybridization with the e_g^{pi} bands. In contrast,the antibonding a_{1g} states display no such hybridization and form a sharppeak. Our results shed new light on the role of the a_{1g} orbitals for themetal-insulator transitions of V2O3. In particular, due to a_{1g} - e_g^{pi}hybridization, an interpretation in terms of molecular orbital singlet stateson the metal-metal pairs along the c-axis is not an adequate description.