With the above functional form for E hyb and E ortho , we now parametrise the sum of the two, i.e. E chem (through Equation ). We choose the O-p and C-p states to have ϵ a = -5 eV and ϵ a = -1 eV, respectively. The projected densities of states resulting from Equation with the chosen ϵ a for the O* and C* also qualitatively agree with our DFT calculated projected density of states shown in Figure , where the localised O* states (shown in orange) are consistently lower-lying in energy as compared to those of C* (shown in purple). Note that the adsorbate projected density of states of both O* and C* show similar features to experimental X-ray photoemission spectra, such as localised states on either side of the d-band from Ref for Cu and Ni, which further validates our approach of using a single renormalised energy for O* and C*.