Having generated the fragments for parametrization, the dihedral angle to be scanned must be assigned a SMIRKS Native Open Force Field (SMIRNOFF) format parameter for incorporation into the FF. When adding any new parameter to a force field, a trade-off between accuracy and transferability must generally be made to avoid the proliferation of parameters and/or atom types. However, in the case of bespoke parametrization, accuracy is favored, and so highly specific encodings are used to ensure the patterns can only be re-used in similar chemical environments, rather than being applied to chemistries that they were not intended to cover. Each fragment is considered to be the minimum electronically decoupled substructure that preserves the local chemical environment of the torsion (due to the conservation of the WBO). Hence, the maximum common substructure between the parent and fragment molecules is embedded into the SMIRKS pattern used to label the scanned dihedral. This SMIRKS pattern is produced by the ChemPer package , and is linked to the generated bespoke torsion parameters, thus facilitating transferability between the fragment and the parent, as well as any other molecules that share this exact substructure (common in studies of congeneric series, as we shall show later). Figure shows an example of a molecule, and the corresponding fragment, alongside the SMIRKS pattern generated for the highlighted torsion scan. The reader does not need to be too familiar with SMIRKS patterns to recognize that every possible attribute has been added to the pattern, making it highly specific to the molecule under study.