Morse potential parameters of dissipative particle dynamics force fields for non-polarizable water models

Abstract

The Morse potential parameters compatible with dissipative particle dynamics (DPD) for water are determined by the Ornstein-Zernike (OZ) equation with the hyper-netted chain (HNC) closure. The present study verifies that the HNC approximation is accurate for a DPD system described by the soft repulsive and Morse potentials. Firstly, we demonstrate that the modified form of the Morse potential is necessary for the numerical solution of the OZ/HNC equations. Subsequently, the Morse potential parameters for mimicking SPCE, TIP3P, TIP4P, and TIP5P water models within the DPD framework are determined by mapping the radial distribution function (RDF) in the HNC approximation to those of all-atom simulations. The first-peak positions and heights of the center-of-mass RDFs for all-atom water models are successfully reproduced by DPD simulations using the determined parameters. The OZ/HNC results for the RDFs and pressures, calculated for the obtained water models, are in satisfactory agreement with the DPD results. Moreover, we investigate how the addition of the Morse potential term to the solute-solvent interaction manifests itself in the solution properties. Major effects of the Morse potential are found in the solute-solvent RDF and the potential of mean force (PMF) between a pair of solutes. We discuss the molecular mechanism underlying the effects induced by the Morse potential in detail.