A two-dimensional model of water: Theory and computer simulations

We develop an analytical theory for a simple model of liquid water. We appl y Wertheim's thermodynamic perturbation theory (TPT) and integral equation theory (IET) for associative liquids to the MB model, which is among the si mplest models of water. Water molecules are modeled as 2-dimensional Lennar d-Jones disks with three hydrogen bonding arms arranged symmetrically, rese mbling the Mercedes-Benz (MB) logo. The MB model qualitatively predicts bot h the anomalous properties of pure water and the anomalous solvation thermo dynamics of nonpolar molecules. IET is based on the orientationally average d version of the Ornstein-Zernike equation. This is one of the main approxi mations in the present work. IET correctly predicts the pair correlation fu nction of the model water at high temperatures. Both TPT and IET are in sem i-quantitative agreement with the Monte Carlo values of the molar volume, i sothermal compressibility, thermal expansion coefficient, and heat capacity . A major advantage of these theories is that they require orders of magnit ude less computer time than the Monte Carlo simulations. (C) 2000 American Institute of Physics. [S0021-9606(00)50806-X].