The most prominent introduction of molecular corrections in heterogeneous catalysis is the correction of the O 2 molecule, first introduced by Nørskov et al. to explain the origin of the overpotential for oxygen reduction . They recognized that the highspin ground state of O 2 is poorly described with DFT, leading to large errors of ∼70 kJ mol -1 in the water splitting reaction. To avoid this issue, they used the experimental reaction energy for water splitting 2