Association in a four-coordinated, water-like fluid

摘要

A four-site, network forming fluid is investigated as a model for the thermodynamic and structural properties of water. Water is represented as a hard sphere with intermolecular association interactions between hydrogen and electron lone pair sites described using the sticky hard sphere limit. This primitive model is analyzed using Wertheim's multidensity graph formalism within the ideal network approximation. Both the associated Ornstein-Zernike integral equation theory, under Percus-Yevick-type closure conditions, and first-order thermodynamic perturbation theory are used to derive analytical results, that mimic, at least qualitatively, some of the features of water. Equations of state, the isothermal compressibility, the heat of vaporization, the heat capacity, and the (classical) critical exponents are determined. The pair correlation function and the structure factor are derived, the latter displaying a prepeak at small k indicative of cluster formation. Both the thermodynamic and structural properties are expressible using the average number of hydrogen bonds per molecule N_(hb), which is determined self-consistently within the theory.