The binding energies of the *O, *OH and *OOH intermediates were then calculated by adsorbing each molecule on top of the metal sites on the relaxed surfaces of the slab with the lowest surface energy. Both A and B sites on the surface of the spinel catalysts were considered. The top two layers, along with the molecules, are allowed to relax for two steps while the bottom layers are kept fixed. The energies of each slab were calculated based on the same parameters used to calculate the surface energies in the previous step. The adsorption energies of the OER intermediates on each slab are subsequently calculated using the following equations :