This can be tentatively attributed to the fact that many (approximately 65%) of the to some specific materials, we find that, similar to the previous scenario, often a particular feature of a MOF tends to magnify the expected deviations between LJ FFs. For example, in addition to OSOMIT, HELCUY, and GIMVAA, cluster I in Figure (c) contains other Znmetal MOFs such as BEPNIV (Figure , top panel on the right) for which confinement effects cannot explain the observed sensitivities as these structures are quite open and feature relatively larger pores. These materials do however contain open metal sites (OMS). As Zn is defined by a smaller LJ collision diameter in UFF, the closest distance of approach between adsorbing CO2 and the OMS is shorter, which leads to an exponential increase in the electrostatic contributions to the interactions in these systems. This generally results in more sporadic adsorption behaviours using UFF parameters. From this observation we expect that large uncertainties are likely to be encountered when: (1) MOFs contain OMS that are accessible to the adsorbates; (2) the OMS belongs to a metal in which the difference in atomic diameters between LJ FFs is significant (e.g., Zn, Fe, Ti, Tc, and Ru); and (3) the partial charge assigned to the metal is sufficiently large. Caution is therefore warranted when interpreting the adsorption behaviours in MOFs with OMS using generic LJ FFs, particularly as they often fail to reproduce the adsorption data of their experimental counterparts. Combined, the materials described here and in the previous scenario explain why poorer correlations between LJ FFs are observed using EQeq (Figure (a, e)), and why 𝜌 𝜌 for CO2 in Figure .