Is there a second critical point in liquid water?

Abstract

The supercooled and stretched regions of the phase diagram of simulated liquid water are investigated by calculating the equation of state of the ST2 and TIP4P pair-potentials. We find that simulated water does not display a re-entrant spinodal and that the projection of the density maximum line in the plane of pressure and temperature becomes positively sloped on stretching. The well-known anomalous behavior of supercooled water is tentatively associated with the existence of an inaccessible critical point. Evidence is presented that suggests the association of this new critical point with the transition between low density and high density amorphous solid water. We show how the observed transformation behavior of the two forms of amorphous solid water can be explained in terms of a first order phase transition, via a consideration of the limits of metastability associated with this kind of transition, and support this interpretation with simulations of the amorphous solid. We therefore propose a phase diagram which accounts for the behavior of both liquid and amorphous solid water.

Liquid-liquid critical point in a Hamiltonian model for water: analytic solution

“…The two-critical-point hypothesis [33][34][35] interprets the increasing in the response functions as a divergence associated with a critical point in the supercooled liquid region. This critical point, at temperature lower than the gas-liquid critical point, is predicted at the end of a first-order phase-transition line that separates two liquid phases, a low-density liquid (LDL) and a high-density liquid (HDL), considered as metastable counterparts of a low-density amorphous and a high-density amorphous, whose first-order transition line has been studied experimentally [14].…”

“…Water shows an anomalous behavior at low temperatures [1][2][3], that has led to an extensive experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16], theoretical [1,2,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] and numerical [1][2][3][33][34][35][36][37][38][39][40][41][42] study. The main anomalies are a rapid increase of the absolute magnitude of isothermal compressibility [5], isobaric heat c...…”

Theoretical Studies on the Structure and Dynamics of Water, Ice, and Clathrate Hydrate

“…Later, a high-density liquid to low-density liquid (HDL-LDL) phase transition was reported based on computer simulations of supercooled water. [15][16][17][18][19][20][21] However, such a liquidliquid transition has not been observed in a laboratory experiment because it is located in the deeply supercooled region. It was suggested that the transition is responsible for various anomalies in water by both statistical mechanical calculations with simple models and MD/MC simulations in which a nucleation is suppressed in a short period.…”

“…The diameter of the carbon nanotube plays a crucial role in determining a size of ice nanotube. At p zz ¼ 50 MPa, a square ice nanotube forms in (13,0) and (14,0) carbon nanotubes, and pentagonal, hexagonal, and heptagonal ice nanotubes form in (15,0), (16,0), and (17,0) systems, respectively. In the largest (18,0) carbon nanotube, however, no crystalline structure has been found without a kind of ''help gas'' within the same simulation period as the others.…”

“…13,14 Although still controversial, the liquidliquid transition of water has been implied by molecular simulation in a metastable supercooled region inaccessible by experiment. [15][16][17] The transition of confined water in the rigid slit pore is a liquid-solid polyamorphic transition, and its first-order character is much clearer than that ever found in bulk water by simulation. This is also an uncommon example of a glass transition during which a liquid freezes into an amorphous solid via a first-order transition.…”