The model reproduces two important features present in the DFT calculated energies. First, the variation of E chem for O* and C* with ϵ d in Figures ) show nearly linear behaviour up to ϵ d ≈ -3 eV. At more negative ϵ d values, E chem decreases, consistent with the DFT computed trends in Figure ). Second, the lack of scaling between different rows of transition metals is also seen in the model chemisorption energies. Figure shows E chem for O* and C*, plotted against each other. Similar to the trends from DFT calculations in Figure ), taken together the points do not scale, but they do scale when each transition metal row is plotted separately, up to the weak binding noble metals. Having developed and parameterised the model, we now use it to explain the variation of the DFT energies with ϵ d in Section IV.