Overall, we achieve mean unsigned errors of 0.024 g/cm 3 , 0.79 kcal/mol and 1.17 kcal/mol in the prediction of liquid densities, heats of vaporization and free energies of hydration for a benchmark set of 109 molecules, compared to experiment. This accuracy is particularly impressive compared to standard, transferable force fields when considering heats of vaporization and liquid densities. While competitive with many transferable FFs, there is substantial room for improvement in the prediction of hydration free energies. This is particularly highlighted when comparing the QUBE data in Table with OPLS3, or when considering the larger molecules, captan and bromacil, in Table . Importantly, however, we emphasize that to describe all molecules in the benchmark data set, we have only fit 8 parameters (the van der Waals radii of eight elements in vacuum) to experimental data (Table ). This reduction in empiricism has two key advantages. Firstly, it has the potential to substantially simplify the FF fitting process, since the parameters come directly from QM and do not rely on extensive collection of experimental fitting data, which is timeconsuming for small molecules, and is rarely done for larger molecules. Secondly, the ease of FF design presents the opportunity to derive new protocols, and move beyond the standard functional form of the FF whilst retaining the ability to derive non-bonded parameters for large molecules. Opportunities for FF improvement include: i) update of the atoms-in-molecule partitioning scheme, ii) the introduction of more rigorous descriptions of van der Waals interactions, 100-102 iii) inclusion of explicit polarization, iv) a more accurate functional form for the short-range repulsion, 28,100 v) investigation of a QUBE-compatible water model 103 and vi) the investigation of Lennard-Jones combination rules. Such efforts would typically require significant re-fitting of the parameter libraries for transferable FFs.