In that same study, the authors proposed that each atom should have a unique effective ionisation energy, derived from the partitioned atomic electron density, which affects the scaling relationship in eq 5. An additional consideration is that the dispersion coefficient (B i ) should be viewed as an effective interaction, taking into account not only the dipole-dipole, but also higher-order (dipole-quadrupole etc) contributions to dispersion. It has been shown that physics-based derivations of B i tend to therefore be lower than the effective coefficients in common MM force fields. To take both of these factors into account, we test here the effect of introducing additional flexibility in the definition of the dispersion coefficient: