• Harmonic bond stretches: 42 out of 88 parameters were optimised. • Harmonic angle bending: 25 out of 40 parameters were optimised. • Proper torsions: 53 out of 167 torsion parameters were optimised. Improper torsions were retained at their Sage values along with the 1-4 non-bonded scaling factor. ForceBalance was used to then optimise the parameters to reduce structural and energetic differences between the accurate QM reference data and the MM predicted values. The fitting used exactly the same optimisation settings as the fitting of OpenFF-Sage. Input and output files may be found in the Supporting Data. To enable a fair comparison of the final DE-FF with a LJ-based FF, we also trained an alternative Sage-style force field to the same reduced target dataset. All nonbonded parameters were held fixed and the same valence terms were optimised starting from their Sage values.