Tetrahedrality, hydrogen bonding and the density anomaly of the central force water model. A Monte Carlo study.

V Ravnik,O Pizio,B Hribar-Lee,M Lukšič

doi:10.5488/cmp.24.33503

Abstract

Monte Carlo computer simulations in the canonical and grand canonical statistical ensemble were used to explore the properties of the central force (CF1) water model. The intramolecular structure of the H2O molecule is well reproduced by the model. Emphasis was made on hydrogen bonding, and on the tehrahedral, q, and translational, τ, order parameters. An energetic definition of the hydrogen bond gives more consistent results for the average number of hydrogen bonds compared to the one-parameter distance criterion. At 300 K, an average value of 3.8 was obtained. The q and τ metrics were used to elucidate the water-like anomalous behaviour of the CF1 model. The structural anomalies lead to the density anomaly, with a good agreement of the model’s density with the experimental ρ(T) trends. The chemical potential-density projection of the model’s equation of state was explored. Vapour-liquid coexistence was observed at sufficiently low temperatures.

Highlights

Water is one of the most important substances on Earth
We studied the molecular geometry of the CF1 water, as well as the effect of temperature and density on it
Two criteria were used to determine the average number of hydrogen bonds: the simplest one-parameter distance criterion based on the integration of the OH radial distribution function and an energy criterion based on the pair energy distribution function

Summary

Introduction

Water is one of the most important substances on Earth. It is a key player in a vast variety of biological, geological, environmental, engineering, and technological processes. In 1975, Stillinger, Lemberg and Rahman proposed an isotropic coarse-grained central force (CF) model of water [2,3,4] and later introduced some improvements [5]. In this model, water is regarded as a weak electrolyte, where oxygen and two hydrogens spontaneously form ion-triplets, i.e., a H2O molecule. The model has been used to study solvation of ions [7,8,9,10] and of hydrophobic solutes [11, 12] as well as at the interface with a planar wall (electrode) [13,14,15]

Methods

Results

Conclusion