1302.5691 (Vincent Holten et al.)

Nature of the anomalies in the supercooled liquid state of the mW model
of water    [PDF]

Vincent Holten, David T. Limmer, Valeria Molinero, Mikhail A. Anisimov

The thermodynamic properties of the supercooled liquid state of the mW model of water show anomalous behavior. Like in real water, the heat capacity and compressibility sharply increase upon supercooling. One of the possible explanations of these anomalies, the existence of a second (liquid-liquid) critical point, is not supported by simulations for this particular model. In this work, we reproduce the anomalies of the mW model with two thermodynamic scenarios: one based on a non-ideal "mixture" with two different types of local order of the water molecules, and one based on weak crystallization theory. We show that both descriptions accurately reproduce the model's basic thermodynamic properties. However, the coupling constant required for fitting the power laws implied by weak crystallization theory is found not to be physically meaningful. For the two-state approach, the direct computation of the low-density fraction of molecules in the mW model is in agreement with the prediction of the phenomenological equation of state. Unlike the possibility in real water, in the mW model the non-ideality of the "mixture" of the two states never becomes strong enough to cause liquid-liquid phase separation, also in agreement with simulation results.

View original: http://arxiv.org/abs/1302.5691