Monte Carlo simulations of fluid systems of waterlike molecules

In an attempt to understand the salient thermodynamic features of liquid water in relation to the molecular interactions in the system, Monte Carlo simulations have been performed on a system of 91 hard spheres representing waterlike molecules with extremely simple short-range interactions. The thermodynamic equilibrium properties, including the free energy and equation of state, are evaluated. The agreement between the energy, entropy and free energy of physical water and of the model is reasonable. It appears that an anomaly in the thermal expansion, as exists in physical water, can be observed when a preference for tetrahedral coordination is superimposed on the hard spheres. When additionally the spheres are made polar, the anomaly persists.