There would be of course no need for such correction terms if more accurate forcefields were available. Thus beyond empirically correcting forcefield errors, the ML correction terms are useful to flag at essentially no computing cost molecules for which predictions are likely to deviate significantly from experimental data. This should be useful to help focus timeconsuming forcefield parameterization efforts, or as part of automated workflows to decide 20 whether to embark in bespoke forcefield parameterization for a given compound. Finally, the methodology presented here could be applied to other scenarios where FEP is used extensively, for instance relative or absolute protein-ligand binding free energy calculations.