  We present the results of an LDA and LDA+U band structure study of the
monoclinic and the corundum phases of V2O3 and argue that the most prominent
(spin 1/2) models used to describe the semiconductor metal transition are not
valid. Contrary to the generally accepted assumptions we find that the large on
site Coulomb and exchange interactions result in a total local spin of 1 rather
than 1/2 and especially an orbital occupation which removes the orbital
degeneracies and the freedom for orbital ordering. The calculated exchange
interaction parameters lead to a magnetic structure consistent with experiment
again without the need of orbital ordering. While the low-temperature
monoclinic distortion of the corundum crystal structure produces a very small
effect on electronic structure of v2o3, the change of magnetic order leads to
drastic differences in band widths and band gaps. The low temperature
monoclinic phase clearly favors the experimentally observed magnetic structure,
but calculations for corundum crystal structure gave two consistent sets of
exchange interaction parameters with nearly degenerate total energies
suggesting a kind of frustration in the paramagnetic phase. These results
strongly suggest that the phase transitions in V2O3 which is so often quoted as
the example of a S=1/2 Mott Hubbard system have a different origin. So back to
the drawing board!
