, where U Single-Guest is the internal energy of a single guest molecule and n is the number of guest molecules per formula unit MOF. The adsorption energy can then be approximated as E Ads = E MOF-Guest + E Guest-Guest . Note that all terms discussed here are functions of the number of guest molecules n and temperature T . Yet we suppressed these here, to improve the readability. We used the unit of energy " kJ • mol f.u.