As outlined in Figure (a), for each choice of force field design protocol (Table ), the Force-Balance software was employed to optimise the set of fitting parameters. These parameters were the R f ree i parameters of H, C, N and O (eq 8), and optionally the dispersion rescaling parameters α and β (eq 11). Where Lennard-Jones parameters were included on polar hydrogen atoms, it was found that a separate R f ree i parameter was required for these atoms.