Oxidation energies of transition metal oxides within the GGA+U framework

The energy of a large number of oxidation reactions of 3d transition metal oxides is computed using the generalized gradient approach (GGA) and GGA+U methods. Two substantial contributions to the error in GGA oxidation energies are identified. The first contribution originates from the overbinding of GGA in the O-2 molecule and only occurs when the oxidant is O-2. The second error occurs in all oxidation reactions and is related to the correlation error in 3d orbitals in GGA. Strong self-interaction in GGA systematically penalizes a reduced state (with more d electrons) over an oxidized state, resulting in an overestimation of oxidation energies. The constant error in the oxidation energy from the O-2 binding error can be corrected by fitting the formation enthalpy of simple nontransition metal oxides. Removal of the O-2 binding error makes it possible to address the correlation effects in 3d transition metal oxides with the GGA+U method. Calculated oxidation energies agree well with experimental data for reasonable and consistent values of U.