Interparticle interactions between water molecules

Makoto Yasutomi

doi:10.3389/fphy.2014.00064

Abstract

We determined many functional representations of interparticle interactions between water molecules, all of which reproduce the experimentally measured density-temperature relation at 1 bar with an accuracy better than obtained by previous models. Numerous similar descriptions of pair interactions will be discovered increasingly in the coming years, which will help us to understand why solid water has polymorphic structures and why liquid water has a large number of anomalies. We used a self-consistent Ornstein-Zernike approximation (SCOZA) with a potential given by multi-Yukawa terms. Because any smooth potential function can be fitted by multi-Yukawa terms, the method can be applied to various types of fluids. We also present a new simple fitting technique that makes the application of the SCOZA to any type of liquid much easier compared to a conventional Yukawa fit. Our new SCOZA fitting technique is among the most useful methods for determining the pair interaction between molecules of any liquid, and the potential will be helpful in improving realistic models.

Highlights

The thermodynamic properties of liquid water can be derived by using thermodynamics and statistical mechanics if the interparticle interactions between water molecules are understood
The self-consistent Ornstein-Zernike approximation (SCOZA) is applicable to fluids with a large variety of smooth potential functions because they may be fitted with high accuracy by multi-Yukawa terms or screened power series (SPS)
We can obtain a tail given by multi-Yukawa terms in a few minutes of computer time almost independently of N, and it makes the application of the SCOZA to any liquid much easier than a conventional Yukawa fit

Summary

INTRODUCTION

The thermodynamic properties of liquid water can be derived by using thermodynamics and statistical mechanics if the interparticle interactions between water molecules are understood. It does not seem to be so easy to elucidate the physics underlying the anomalous behaviors of liquid water This is because a realistic model includes a great number of miscellaneous effects, even if it is highly precise and is able to reproduce experimentally measured data. The simplified potential models presented so far have not been shown to reproduce quantitatively the experimental behaviors of liquid water with sufficient accuracy. This prevents the formation of conclusive explanations of the density anomaly because the thermodynamic properties of liquids depend strongly on the interparticle interactions. The equations to be solved are the OZ relation (1) with the thermodynamic consistency relation (5) supplemented with the closure relations (2) and (3)

SCOZA FOR A FLUID

MODELS OF THE POTENTIAL BETWEEN WATER MOLECULES

A NEW SIMPLE TECHNIQUE OF FITTING BY MULTI-YUKAWA TERMS

SUMMARY AND DISCUSSION