For this study, the uncertainty of the species' entropy was not taken into account, although it should be noted that this value is not zero. However, for this model, all of the surface species are small molecules with relatively constrained motion across the surface, so it was deemed reasonable to neglect. Thus, only the uncertainty in the species enthalpy was considered. The enthalpic portion of the uncertainty was quantified by determining the uncertainty in each species binding energy, and then using that as the uncertainty in the heat of formation for each species. The uncertainty in the binding energy was supplied as P (✓) to the DFT model. The average 2 error for species calculated using DFT was 0.299 eV.