The Drude polarizable force field displayed an even poorer correspondence with the XDM C 6 coefficients than the three non-polarizable models. Several atom types in the Drude force field have dispersion coefficients that are many times greater than the XDM values. It is possible that the increased number of terms in this force field, due to the incorporation of the polarizability, cause the parameters to be underdetermined. The parameter-fitting process could benefit from additional constraints, such as physically-reasonable molecular dispersion coefficients derived from XDM. Some standard water models, such as TIP3P, have dispersion coefficients that are very similar to the XDM and experimental values. Other models, such as TIP4P-D and SWM4-NDP, overestimate the magnitude of the dispersion coefficient by up to 50%. Thus, the C 6 coefficient may be a worthwhile term to consider in the evaluation of water models in order to ensure the dispersion interactions are physically realistic.