While some parameter sets we demonstrate in this work improved both enthalpies of vaporization and enthalpies of mixing, in our view, improvements in the properties of mixtures are a better metric of force field improvement than pure or phase change properties for force fields intended for use in biomolecular simulations, since simulations typically take place in mixed aqueous or other liquid phases. This is supported by our finding that force fields trained against mixture data improve predictions of Δ , whereas force fields trained against only pure data (including Δ