To assess the quality and transferability of the parameter sets produced by our optimization, we tested them on a set of physical properties (29 𝜌 𝐿 , 318 𝜌 𝐿 (𝑥), 29 Δ𝐻 𝑣𝑎𝑝 , and 236 Δ𝐻 𝑚𝑖𝑥 (𝑥)) for a new set of molecules and molecular pairs, which serves as the test set. This data set was curated for our previous work, and its selection and composition are discussed there. Physical properties in this set are either hand-curated from literature (𝜌 𝐿 , Δ𝐻 𝑣𝑎𝑝 ), or are selected automatically from the NIST ThermoML Archive. Benchmarking simulations are performed using the same OpenFF Evaluator workflows as simulations used in the optimization process. Out of the 10 optimizations run, 4 of them terminated early after the surrogate optimizer could not find an improved solution. This is related to the issues with ARD noted in section 2.2. This suggests that further research is needed to improve the robustness of the surrogate model. Optimizations used between 15-25 total simulations, compared to the 12 used in the simulation-only optimization.