Bulk and surface properties of spinel Co3O4 by density functional calculations

DFT calculations are employed to bulk and surface properties of spinel oxide Co3O4. The bulk magnetic structure is calculated to be antiferromagnetic, with a Co2+ moment of 2.631 μB in the antiferromagnetic state. There are three predicted electron transitions O(2p) → Co2+(t2g) of 2.2 eV, O(2p) → Co3+(eg) of 2.9 eV and Co3+(t2g) → Co2+(t2g) of 3.3 eV, and the former two transitions are close to the corresponding experimental values 2.8 and 2.4 eV. The naturally occurring Co3O4 (1 1 0) and (1 1 1) surfaces were considered for surface calculations. For ideal Co3O4 (1 1 0) surfaces, the surface relaxations are not significant, while for ideal Co3O4 (1 1 1) surfaces the relaxation of Co2+ cations in the tetrahedral sites is drastic, which agrees with the experiment observation. The stability over different oxygen environments for possible ideal and defect surface terminations were explored.