where the .offxml file contains all the valence and non-bonded parameters fit in the current study. Smirnoff-plugins then enables the use of custom functional form force fields with the entire OpenFF fitting software stack including Evaluator 20 , ForceBalance and BespokeFit . Smirnoff-plugins is not limited to nonbonded interactions and can be used to supplement or replace any part of the force field. This will be critical for exploratory investigations into improving force field accuracy via new nonbonded and valence functional forms, such as Urey-Bradley cross coupling terms.