LIMITS OF STABILITY OF THE LIQUID-PHASE IN A LATTICE MODEL WITH WATER-LIKE PROPERTIES

Explicit study of the hydrogen bond network in water offers a microscopic approach to understanding the anomalous properties of water, while an alternate, thermodynamic approach is offered by the reentrant limit of stability (spinodal) conjecture. To relate the two approaches, we develop a lattice model based on microscopic considerations. We show that the model displays anomalous thermodynamic behavior that is in qualitative agreement with the behavior of water. We study the model in the mean field approximation and by numerical simulations. We explicitly demonstrate the interrelation between density maxima and the reentrance of the spinodal: both originate from the contribution of orientational degrees of freedom to the thermodynamics of the system. The metastable liquid state is bounded by a spinodal at positive pressures as well as negative pressures, where the positive pressure spinodal is the limit of stability with respect to the solid state. The liquid-gas and liquid-solid spinodals form a continuous locus, but the ''critical'' properties of these two spinodals are quite different. While the response functions (specific heat, compressibility) diverge at liquid-gas spinodal, at the liquid-solid spinodal they do not-even though the response functions tend to higher values in the same fashion as occurs near the liquid-gas spinodal.