Liquid−Liquid Phase Transition in Confined Water: A Monte Carlo Study‡

Amorphous solid water displays two distinct phases, low density amorphous ice (LDA) and high density amorphous ice (HDA) that transform into each other via a first order phase transition. 1 Recently, it has been proposed that the transition line between these known phases can be extrapolated to higher temperatures into the metastable liquid region of the phase diagram, raising the intriguing possibility of the coexistence of two liquid phases and of the existence of a second critical point in the metastable liquid. 2 This “liquid-liquid phase transition” scenario has been supported by computer simulations with various effective interaction potentials, specifically with the ST2, 2,3 TIP4P, 2,4 and the SPC/E 5 potentials. Also, it has been shown that simple lattice models of water 6 as well as simplified spherically symmetric soft core potentials 7 and mean field approaches 8 can display a liquid-liquid-phase transition. Experimental evidence for the existence of the second critical point is difficult to obtain, since the strong nucleation tendency in the region of the phase diagram, where the second critical point might be found, makes it impossible to keep water in the liquid state. 9