It is difficult to determine which torsion parameters need improvement from optimized geometries since any given optimized geometry is a result of all applied parameters and not simply a single torsional parameter. In an effort to determine which parameters might be particular problematic, one helpful analysis is to tabulate the torsion parameters that are over-represented in the molecules that show a higher TFD when compared to the rest of the molecules. Figure shows the distribution of torsion parameters in higher TFD cases when compared to the distribution of that same torsion parameter on the whole set of molecules under consideration. Torsion parameters t25, t49, t55, t88, t91, t103, t134, t135, t154, t158 are the top ten parameters that are over-represented in cases with higher deviations, with the corresponding SMIRKS patterns tabulated in SI Table . t154 shows particularly high overrepresentation and is another case of a torsion involving hypervalent sulfur, with the SMIRKS pattern Improper torsions need a special explanation as they are not optimized and remain at their legacy (Parsley 1.3.0) values. Figure shows the error distribution among the improper angle values when compared to QM structures on the whole benchmark set. Some of the deviations in improper angles around chiral atoms have a larger value when the out-of-plane atom in the MM optimized conformer is a mirror image of the QM conformation, but no filter was applied to weed out these cases, which thus may appear to be in substantial error even when they are not. Nitrogen-centered impropers, especially parameter i4 ( This particular parameter has a small force constant of 1 kcal/mol, which allows the geometry to range from planar (0 • ) to pyramidal (109.5 • ) in different chemical contexts. Thus, we see a wider distribution of deviations from -60 to +60 degrees in the improper angles where i4 is applied when compared to QM. ]") has a wider distribution as it covers both planar and pyramidal instances and can be improved by binning chemistries based on structural differences, and splitting the current parameter to apply to subsets with distinct behaviors. This data suggests that, as we expect, there is substantial room to improve improper torsions in subsequent iterations of the force field.