The systematically more positive field components observed with the additive models appear counterintuitive given that Amber and Charmm field strengths were substantially more negative than those of AMOEBA when projected along the vector perpendicular to the proline ring (Fig. ). However, the projection process may conflate differences in field magnitude and direction between the force fields, while the comparison of individual Cartesian components with DFT more fairly characterizes both properties. Additionally, the relatively limited data used in each comparison (30 points, one for each Cartesian component of the field in ten separate trajectory frames) could potentially result in dataset bias, and we have not attempted to ensure structural diversity between the analyzed frames, preferring instead to use the whole trajectory length to extract time-separated frames at regularly spaced intervals. The confidence intervals in the R 2 values (Fig. , estimated by resampling with replacement), almost never overlap for the ONETEP/AMOEBA and ONETEP/additive models, suggesting that the improved correlation observed with AMOEBA is likely to be statistically significant if the whole population were compared. To broaden the structural diversity of the dataset while restricting the overall size to a computationally-tractable number of full-DFT electric field calculations, we similarly analyzed alternative CypA-peptide substrate complexes.