A more affordable way to describe the interactions between the atoms of a MOF is to use a classical force field. For example, the universal force field (UFF) can predict the mechanical properties of a MOF with similar accuracy as DFT. However, Figure shows that this force field significantly underestimates the heat capacity. If we softened the spring constants between metals and linkers, we can obtain better agreement with the DFT results. However, one would need a metal-linker dependent correction factor to correctly capture the subtleties of the chemistry, which limits the usefulness of the UFF force field to predict the heat capacity of MOFs. Further analysis (see SI) shows that the deficiencies of the UFF force field is mainly due to the metal-linker interactions, whereas the linker contributions are well described. As MOF-74 has relatively high metal content, the errors are relatively large.