In contrast, even for this small test set, we found one missing bond parameter and six missing angle parameters using a standard transferable FF. The QUBE predicted values for these terms along with the OPLS atom types are shown in Tables and. In practice, these parameters would be inferred from similar atom types or re-parameterized by the user, which may introduce inaccuracy. QUBE allows the user to rapidly and automatically derive all necessary parameters with no compromise in accuracy. In this study, the QUBE FF maintains a low mean percentage error in MM vibrational frequencies of 6.5% (MUE of 54 cm -1 ), which is very similar to the values initially reported reaffirming the wide-scale applicability of the method. We note that the modified Seminario method derives the force constants directly from the QM Hessian matrix with no information required about the torsional and non-bonded parameters. In practice, these components of the FF will also contribute to molecular vibrations. It appears that slight improvements in accuracy are achievable by fitting the full MM Hessian matrix to the QM Hessian. For example, a MUE of 44 cm -1 is reported using the QMDFF on a set of 22 molecules. Where high accuracy in molecular vibrations is key, for example in spectroscopic applications, it may be desirable to include coupling FF terms which account for off-diagonal terms in the Hessian matrix. However, for our intended applications in computer-aided drug design, we favor the relative simplicity of the modified Seminario method. Given the widespread use of transferable bond and angle parameters, it is worth analyzing to what extent these parameters vary in our benchmark test set. Figure plots the range of QUBE bond lengths and force constants for all atoms defined with CT-CT bond types in the test set, and compares them with the OPLS parameters. Further plots like this for all bonds and angles that are present in at least ten of the molecules in the test set can be found in Figures . As reported previously, the modified Seminario method gives bond-stretching force constants that are on average lower than their OPLS counterpart. The QUBE parameters typically span a range of around 0.05 Å and 100 kcal/mol/ Å2 for the bond length and force constant respectively, indicating that use of a single average, transferable value should not introduce significant error. Interestingly, there is a negative correlation between force constant and equilibrium bond length, supporting the use of bond length to infer force constants in studies. These results indicate that it may be possible to derive more explicit algorithms for 'learning' force field parameters directly from the molecular geometry. We also envisage QUBE parameters as providing a reasonable starting point for optimization if further fitting to QM potential energy surfaces is desired. Torsional parameters, like the bond and angle parameters, were derived separately for each molecule. Due to the use of virtual sites, we found that parameters were often not transferable between similar molecules, and those that were such as methyl group rotations remained close to the initial OPLS parameters. The overall accuracy of the torsional scan fitting was very good when regularization was used and only a handful of molecules with poor predicted energy surfaces required the setting to be switched off. A sample of torsion fitting data taken directly from the QUBEKit output can be found in Figures , along with the overall error and regularization error bias where appropriate. We have also included the dihedral parameters for every molecule in the test set in the Supporting Information along with an analysis in which we have grouped the torsions together based on their OPLS atom types. We envisage these as forming the basis of a community-led library to be used to replace or speed up future fitting efforts.