Differences in the behaviour of n a + f with ϵ d between -3 < ϵ d < 0 for O* and C* cause row-dependence of E ortho and hence E chem . Figure shows the scaling be-tween E ortho of O* and C*; noticeable deviations are seen in linear scaling of E ortho , but also in overlap between the rows of transition metals. Furthermore, differing behaviour of n a + f with ϵ d is a consequence of different ρ aa (ϵ) (determined from Equation ) for different adsorbates, i.e. different ϵ a . As an example, Figure shows ρ aa (ϵ) for C* (puple) and O* (orange) on Rh, a mid-row transition metal. Since ϵ a for C* is more positive than O*, the adsorbate projected density of states broadens and splits differently, resulting in different n a and hence row-dependent scaling behaviour.