Appraisal of dispersion damping functions for the effective fragment potential method

The effective fragment potential (EFP) is a polarizable force field whose physically-motivated functional form is parameterized in an automated way from ab initio calculations, and whose dispersion potential has been suggested as a correction for Hartree-Fock or density functional theory calculations. However, the parameter-free dispersion damping potentials that are currently used in EFP do not follow from a rigorous derivation and do not satisfy simple limits for the dispersion energy. We introduce several new damping expressions that correct these deficiencies, then evaluate their performance alongside existing damping functions using a new database of ionic liquid constituents. This data set, which we call IL195x8, consists of complete-basis coupled-cluster interaction energies for 195 ion pairs at each of 8 different intermolecular separations. Ultimately, we recommend a new parameter-free dispersion damping function as a replacement for the one that is currently used in EFP.