reference basis sets The methods that have been introduced in prior sections rely on an atomic basis set, with one reference species defined per element. Depending on the scheme, these references may be gasphase or adsorbed species, but the approaches presented thus far effectively act as adsorption energy corrections. They ensure that gas-phase reaction energies are consistent with ATcT, and that surface reactions are consistent with DFT, while adsorption energies are adjusted in various ways to ensure this is the case. Each method makes different assumptions about how to adjust the adsorption energies. However, since surface reaction enthalpies are rarely known, the most common approach is to assume that DFT surface reaction enthalpies are accurate. The logic for this is that error cancellation in DFT is likely the largest for surface reactions since both products and reactants have similar electronic environments (adsorbates on surfaces).