Classical density-functional theory of inhomogeneous water including explicit molecular structure and nonlinear dielectric response

TL;DR

This paper develops a classical density-functional theory for inhomogeneous water that explicitly accounts for molecular structure and nonlinear dielectric response, accurately reproducing key physical properties and behaviors.

Contribution

It introduces a free-energy functional framework that captures water's molecular orientation effects and nonlinear dielectric behavior, improving upon previous models.

Findings

Accurately reproduces dielectric response and site-site correlations.

Predicts surface tension, bulk modulus, and phase coexistence.

Demonstrates nonlinear dielectric response in capacitor simulations.

Abstract

We present an accurate free-energy functional for liquid water written in terms of a set of effective potential fields in which fictitious noninteracting water molecules move. The functional contains an \emph{exact} expression of the entropy of noninteracting molecules and thus provides an ideal starting point for the inclusion of complex inter-molecular interactions which depend on the \emph{orientation} of the interacting molecules. We show how an excess free-energy functional can be constructed to reproduce the following properties of water: the dielectric response; the experimental site-site correlation functions; the surface tension; the bulk modulus of the liquid and the variation of this modulus with pressure; the density of the liquid and the vapor phase; and liquid-vapor coexistence. As a demonstration, we present results for the application of this theory to the behavior of liquid water in a parallel plate capacitor. In particular, we make predictions for the dielectric response of water in the nonlinear regime, finding excellent agreement with known data.