Ab initio study of corundum-like Me2O3 oxides (Me = Ti, V, Cr, Fe, Co, Ni)

Periodic unrestricted Hartree-Fock methods, with all-electron basis sets and a posteriori estimate of correlation energy, have keen used to study the ground-state total energy of the title compounds with rhombohedral R (3) over bar c corundum-type structure. Co2O3 and Ni2O3 are shown to be stable oxides with quite regular binding energies at the athermal limit. The relative stabilities of the AF1 (R3c), AF2 (R (3) over bar) and AF3 (R32) antiferromagnetic structures have been investigated, showing that Cr2O3 adopts the AF1 configuration, while Fe2O3, Co2O3 and Ni2O3 prefer AF2; this is accounted for in terms of sigma- and pi-type superexchange interactions. The spin polarization of electron transfer from O2- to Me3+ has been analysed, showing that only minority-spin electrons are transferred for Me = Fe, Co and Ni, while the total transfer is doubled for the other oxides by the majority-spin contribution.