where 𝜃 stands for force field parameters in the current iteration used in the MM calculation, 𝑑 𝑖 refers to the scaling factors of 0.05 Å, 8 • and 20 • for bond lengths, bond angles, and improper torsion angles, respectively. The values of dimensional scaling factors here were chosen based on chemical intuition given the size scale of typical atomic fluctuations, with the goal that each term in the objective function contributes similarly to the overall objective function and that fluctuations larger than "normal" in a particular coordinate would be penalized. Deviations in proper torsion angles were not included in this objective function since those were fitted with the torsion profile energetics by keeping the dihedral angle constant on a grid of angles, and fitting torsion profiles solely with optimized geometries might introduce numerical artifacts. This is because equilibrium geometries do not provide information about the higher energy regions of energy landscapes that are encountered in a dihedral rotation. Improper torsion parameters were not retrained but instead were held constant, as noted above. Deviations in improper angles were included in the opt-geo target objective function to minimize discrepancies in improper angles of MM optimized structures since impropers were not fit. Particularly, with our very sparse set of improper torsion parameters, planarity is dictated by a balance of angle bending parameters and our (un-changed) improper torsion parameters. Without including some metric of planarity in the fits, angle parameters would be free to change in a way which bends planar groups out-of-plane without this contributing to the objective function, so we included this metric in the opt-geo objective function. The situation should be improved in subsequent work as we introduce a less sparse set of improper torsion parameters and begin to specifically refit these.