All molecules used consist only of elements C, H, O, and N, but a diverse range of chemical fragments, including aliphatic carboxylic acids, amides, aldehydes, and aromatic hydrocarbons, are included to ensure the transferability of the resulting parameters. Two charged molecules are included in the training sets to represent electrostatic environments caused by charged proteins or ligands. For molecules with rotatable bonds, multiple conformations are generated and fitted as if they were independent molecules. Baseline and polarized QM ESPs were evaluated at the MP2/aug-cc-pVTZ QM level of theory, because prior benchmarks of electronic structure methods for molecular mechanics and polarizable force fields suggest that this QM method affords a favorable balance of efficiency and accuracy. The external electric fields used to generate polarized ESPs have a strength of 0.01 a.u. ESPs were computed at Merz-Singh-Kollman (MSK) style grid points 52,60 located outside the van der Waals radii of all atoms using a spacing of 0.126 Å and a density of 17 points per Å 2 for a total of 10 layers.