We also believe that there are two other advantages of using IDACs: First, IDACs for a given solute of interest can be obtained in different solvents, allowing the potential to explore how well a force field represents molecules both as solutes and as solvents. Second, molecules become polarized when transferred from gas phase to water and hydration free energies with conventional force fields (excepting polarizable force fields) might not be able to describe this phenomenon well; parameterization to hydration free energies could even build in systematic error resulting from lack of treatment of polarization. This may be particularly important;