Europhys. Lett.
Volume 70, Number 6, June 2005
Page(s) 782 - 788
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 18 May 2005
Europhys. Lett., 70 (6), pp. 782-788 (2005)
DOI: 10.1209/epl/i2005-10050-2

Covalent bonding and hybridization effects in the corundum-type transition-metal oxides $\chem{V_2O_3}$ and $\chem{Ti_2O_3}$

V. Eyert, U. Schwingenschlögl and U. Eckern

Institut für Physik, Universität Augsburg - 86135 Augsburg, Germany

received 6 January 2005; accepted in final form 28 April 2005
published online 18 May 2005

The electronic structure of the corundum-type transition-metal oxides $\chem{V_2O_3}$ and $\chem{Ti_2O_3}$ 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 3d a1g density of states, which is present in both compounds. The a1g 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 a1g states, which is caused by hybridization with the $e_g^{\pi}$ bands. In contrast, the antibonding a1g states display no such hybridization and form a sharp peak. Our results shed new light on the role of the a1g orbitals for the metal-insulator transitions of $\chem{V_2O_3}$. In particular, due to a1g-$e_g^{\pi}$ hybridization, an interpretation in terms of molecular orbital singlet states on the metal-metal pairs along the c-axis is not an adequate description.

71.20.-b - Electron density of states and band structure of crystalline solids.
71.27.+a - Strongly correlated electron systems; heavy fermions.
71.30.+h - Metal-insulator transitions and other electronic transitions.

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