Ordinary PBE was chosen because of its status as the standard GGA functional, as well as its accurate prediction of CO 2 chemisorption energies . PBEsol was designed to give some improvements in packed solid systems and surface energies . RPBE and revPBE were developed to specifically improve chemisorption energies , and also were observed to give the best compromise between structural parameters and chemisorption energies in diamine-functionalized MOFs . Lastly, vdw-DF2 was selected as a representative fully non-local functional, with density dependence of the non-local correlation (Eq. 12). This functional has also been used in other works studying both chemisorption and physisorption . A more detailed discussion of the different functionals and how their form affects the predicted binding motifs can be found in Section IV.