chemper contains a variety of tools that will be useful in automating the process of chemical perception for the new SMIRKS Native Open Force Field (SMIRNOFF) format as a part of the Open Force Field Consortium [1].

This idea originated from the tools SMARTY and SMIRKY which were designed to use an automated monte carlo algorithm to sample the chemical perception used in existing force fields. SMARTY samples SMARTS patterns corresponding to traditional atom types and was tested compared to the parm99/parm@frosst force field. SMIRKY is an extension of SMARTY created to sample SMIRKS patterns corresponding to SMIRNOFF parameter types (nonbonded, bond, angle, and proper and improper torsions). SMIRKY was tested against our own smirnoff99Frosst

One of the most important lessons learned while testing SMARTY and SMIRKY is that the combinatorial problem in SMIRKS space is very large. These tools currently use very naive moves in SMIRKS space chosing atom or bond decorators to add to a pattern at complete random. This wastes a signficant amount of time making chemically insensible moves. One of the take away conclusions on that project was that future chemical perception sampling tools would need to take atom and bond information from input molecules in order to be feasible [2].

We developed chemper based on the knowledge of the SMARTY project outcomes. The goal here is to take clustered molecular subgraphs and generate SMIRKS patterns. These tools will use information stored in the atoms and bonds of a molecule to drive choices about SMIRKS decorators. Then will automatically generate reasonable SMIRKS patterns matching clustering of molecular subgraphs.

Currently, chemper provides modules for generating SMIRKS patterns from molecule objects and specified atoms. The final product will be capable of clustering molecular fragments based on reference data and then assigning SMIRKS patterns for each of those clusters. See Installing chemper.


CCB is funded by a fellowship from The Molecular Sciences Software Institute under NSF grant ACI-1547580.


    1. Mobley et al. bioRxiv 2018, 286542.

    1. Zanette and C.C. Bannan et al. chemRxiv 2018,