Multipoles as Force Field Parameters - Accuracy and Redundancy

Abstract

Simulation of proteins and other large biomolecules rely on a force field representation of the potential energy surface. Fixed charge force fields, like AMBER, CHARMM, OPLS, and GROMOS, are widely used, however, it is well known that they, due to their simplicity provide an inaccurate description of the electrostatic energy component.In this study, multipoles up to quadrupoles are fitted to reproduce an ab initio electrostatic potential. The accuracy gained by introducing higher order multipoles is significant. However, the inclusion of multipoles as electrostatic parameters is highly associated with additional redundancy among the parameters. In an attempt to resolve redundancy, a large fraction of less important multipoles were identified and eliminated, without affecting the accuracy of the electrostatic potential. Furthermore, it is concluded that the reduced set of chemically important multipoles is transferable to different geometries of the same molecule. This is a promising result with respect to force field development, which highly relies on the assumption of transferability.