Fitting also led to improvements in the accuracy of the torsional energy profiles in the training set (Figure ), although the improvements (red to green) appear less dramatic than for the geometric and vibrational components discussed above. As for the other objective function components, the improvements observed for many torsions come at the expense of decreased accuracy for some others (blue). The RMSE of the MM torsional energy profiles relative to the QM ones in the training set fell from 2.96 to 1.89 kcal/mol, a 36% drop (Table ).