Effects of Bridge Functions on Radial Distribution Functions of Liquid Water

TL;DR

This study enhances the accuracy of radial distribution functions of liquid water by incorporating bridge functions into classical density functional theory, improving upon the hypernetted-chain approximation especially at room temperature.

Contribution

It introduces a method to include bridge functions via a density expansion and factorization approximation, leading to more accurate RDF calculations for liquid water.

Findings

Bridge functions significantly improve RDF predictions.

The method enhances the description of the second peak in oxygen-oxygen RDF.

Numerical results confirm better agreement with experimental data.

Abstract

In this report the radial distribution functions (RDFs) of liquid water are calculated on the basis of the classical density functional theory combined with the reference interaction site model for molecular liquids. The bridge functions, which are neglected in the hypernetted-chain (HNC) approximation, are taken into account through the density expansion for the Helmholtz free energy functional up to the third order. A factorization approximation to the ternary direct correlation functions in terms of the site-site pair correlation functions is then employed in the expression of the bridge functions, thus leading to a closed set of integral equations for the determination of the RDFs. It is confirmed through numerical calculations that incorporation of the oxygen-oxygen bridge function substantially improves the poor descriptions by the HNC approximation at room temperature, e.g., for the second peak of the oxygen-oxygen RDF.