In our simulations of the WT cis-proline complex, the AMOEBA force field consistently showed an offset of ca. +15 to +25 MV cm -1 to Amber or Charmm electric field strengths. Although this trend was internally consistent across simulations and between force fields (Fig. , Table ), the AMOEBA electric fields appeared to differ from those calculated by Camilloni & coworkers in CypA, which were estimated to be at least -40 MV cm -1 at the active site in both the cis-proline and trans-proline ground states. However, our system and methodology also differed substantially from this previous study. Simulations here were performed with a different peptide substrate, applied no NMR restraints to the protein structural ensemble, and calculated fields at both peptide C and N atoms during the projection of the field vector along the peptide normal, rather than only at the N atom. As such, we tested the accuracy of our MM-calculated field strengths by comparison to field strengths calculated with ONETEP DFT on the entire simulation system, which consisted of 19018 atoms. A subset of ten frames extracted at 2.5 ns intervals from the first replicate AMOEBA WT cis-proline simulation was used for comparison. Field vectors were compared directly using their Cartesian x, y, and z components in the simulation frame, rather than any projection along a specific vector. Correlations between the ONETEP DFT and AMOEBA fields were relatively high, with R 2 of 0.75 and 0.92