SMIRKY extends SMARTY, testing our ability to sample over chemical perception trees used for fragment types in SMIRNOFF format force fields. It automatically samples SMIRKS patterns for fragment types for bond, angle, torsion, and nonbonded types then compares the fragment type SMIRKS with that in a reference force field for the same set of molecules. As with SMARTY, the overall goal with SMIRKY is to ensure we can find SMIRKS patterns that sample comparable chemical complexity to that used in our reference force field, smirnoff99Frosst. Scoring works the same as with SMARTY-we evaluate both the total score and the partial score for each iteration. In the case of SMIRKY, a partial score of 100% corresponds to SMIRKY discovering a SMIRKS pattern that matches a single reference fragment type (Equation ).