For all force fields, post-processing of trajectory frames to remove the CypA receptor, solvent and ion coordinates allowed the equivalent calculation of electric fields in the ligand-only system, 𝐸 "⃗ ,/01%2 . Finally, the electric field arising from the protein/solvent/ionic atmosphere of the system and acting on the rotatable amide bond, 𝐸 "⃗ $%& , was calculated via Eqn. 1.