The electronic structure and magnetism of chromia (corundum-type Cr2O3) are
studied using full-potential first-principles calculations. The electronic
correlations are included within the LSDA+U method. The energies of different
magnetic configurations are very well fitted by the Heisenberg Hamiltonian with
strong exchange interaction with two nearest neighbors and additional weak
interaction up to the fifth neighbor shell. These energies are insensitive to
the position of the oxygen states, indicating that magnetism in Cr2O3 is
dominated by direct exchange. The Neel temperature is calculated using the
pair-cluster approximation for localized quantum spins of magnitude 3/2. Very
good agreement with experiment is found for all properties including the
equilibrium volume, spectral density, local magnetic moment, band gap, and the
Neel temperature for the values of U and J that are close to those obtained
within the constrained occupation method. The band gap is of the Mott-Hubbard
type.Comment: 6 pages, 2 eps figure