(123b) LOW TEMPERATURE FLUID-PHASE BEHAVIOR of ST2 Water

We perform histogram-reweighting Monte Carlo simulations of the ST2 model of water in the grand-canonical ensemble in order to investigate its low-temperature fluid-phase behavior. Using Ewald summation treatment of long-range electrostatic interactions, we locate the critical point of the liquid-liquid transition at T = 237 ± 4 K, ρ= 0.99 ± 0.02 g/cc, P =167 ± 24 MPa. Contrary to previous reports in the literature [Brovchenko et al., J. Chem. Phys., 118, 9473 (2003); Brovchenko et al., J. Chem. Phys., 123, Art. No. 044515 (2005)], according to which there are three liquid-liquid transitions in ST2 with simple truncation of electrostatic interactions, and two in ST2 with reaction field treatment of long-range Coulombic forces, we find only one liquid-liquid transition. Our work points to the sensitivity of results to the proper treatment of electrostatic interactions, and to the introduction of artificial constraints that limit the magnitude of density fluctuations.