A theory of the anomalous thermodynamic properties of liquid water

A theory of the anomalous thermodynamic properties of liquid water is presented. The theory is based on a simple model intermolecular potential that contains short-ranged repulsions, hydrogen-bonding attractions, and longer ranged interactions. Cluster theory approximations derived in the previous paper [J. Chem. Phys. 77,1962 (1982)] are used to calculate the thermodynamic energy and free energy for the model fluid as a function of temperature and density. The model fluid is found to have many of the anomalous properties of real water, such as a density maximum at low pressure, a compressibility minimum, and high heat capacity. The model is not a quantitatively accurate one for real water, nor does it have the anomalous properties observed for supercooled water. The reasons for the anomalies of the model fluid are discussed in order to shed some light on the physical basis for these anomalies in real water.