Metastable Criticality in Realistic Classical Models of Water

The hypothesis that water possesses a second critical point at deeply supercooled conditions was formulated to provide a thermodynamically consistent interpretation of numerous experimental observations. A large body of work has been devoted to verifying or falsifying this hypothesis, but no unambiguous experimental proof has been found to date. Here, we use histogram reweighting and large-system scattering calculations to investigate computationally two molecular models of water, TIP4P/2005 and TIP4P/Ice, widely regarded to be among the best classical force fields for this substance. We show that both models possess a metastable liquid-liquid critical point at deeply supercooled conditions and that this critical point is consistent with the 3-d Ising universality class.