PERIODIC UNRESTRICTED HARTREE-FOCK-STUDY OF CORUNDUMLIKE TI2O3 AND V2O3

The ground-state electronic and magnetic properties of rhombohedral Ti 2O3 and V2O3 have been investigated by ab initio all-electron periodic Hartree-Fock calculations. Both unrestricted open-shell and restricte d closed-shell methods have been employed, with basis sets of atomic o rbitals represented by contracted Gaussian-type functions. The t(2g) d egeneracy of d electrons is removed by the rhombohedral field, giving rise to orbital ordering between a(1g) and e(g)(pi) levels. The self-c onsistent-field variational solutions are spin-polarized insulating st ates with single (a(1g)) and double (e(g)(pi)) electron occupations fo r Ti2O3 and V2O3, respectively. Conducting or semiconducting states, w ith different relative energies of a(1g) and e(g)(pi) bands, have also been obtained by changing the c/a ratio of the hexagonal unit cell. T he charge transfer into e(g)(sigma) levels is discussed and compared t o the Cr2O3 and Fe2O3 behavior.