Understanding three-body contributions to coarse-grained force-fields

TL;DR

This paper investigates the impact of three-body interactions on coarse-grained force fields, highlighting the importance of many-body effects in accurately modeling liquids like water and methanol.

Contribution

It demonstrates that separate coarse-graining of two- and three-body forces improves understanding of many-body effects in force-field parametrization.

Findings

Three-body interactions are crucial for accurate water modeling.

Two-body interactions suffice for methanol structural properties.

Naive force-field extensions can lead to unphysical results.

Abstract

Coarse-graining (CG) is a systematic reduction of the number of degrees of freedom (DOF) used to describe a system of interest. CG can be thought of as a projection on coarse-grained DOF and is therefore dependent on the functions used to represent the CG force field. In this work, we show that naive extensions of the coarse-grained force-field can result in unphysical parametrizations of the CG potential energy surface (PES). This issue can be elevated by coarse-graining the two- and three-body forces separately, which also helps to evaluate the importance of many-body interactions for a given system. The approach is illustrated on liquid water, where three-body interactions are essential to reproduce the structural properties, and liquid methanol, where two-body interactions are sufficient to reproduce the main features of the atomistic system.