Quantum-mechanical exploration of the phase diagram of water

Abstract

The phase diagram of water harbours many mysteries: some of the phase boundaries are fuzzy, and the set of known stable phases may not be complete. Starting from liquid water and a comprehensive set of 50 ice structures, we compute the phase diagram at three hybrid density-functional-theory levels of approximation, accounting for thermal and nuclear fluctuations as well as proton disorder. Such calculations are only made tractable because we combine machine-learning methods and advanced free-energy techniques. The computed phase diagram is in qualitative agreement with experiment, particularly at pressures $\lesssim$8000 bar, and the discrepancy in chemical potential is comparable with the subtle uncertainties introduced by proton disorder and the spread between the three hybrid functionals. None of the hypothetical ice phases considered is thermodynamically stable in our calculations, suggesting the completeness of the experimental water phase diagram in the region considered. Our work demonstrates the feasibility of predicting the phase diagram of a polymorphic system from first principles and provides a thermodynamic way of testing the limits of quantum-mechanical calculations.

References in corpus (13)

• Competing quantum effects in the dynamics of a flexible water model
• How van der Waals interactions determine the unique properties of water
• What ice can teach us about water interactions: a critical comparison of the performance of different water models
• On the accuracy of the MB-pol many-body potential for water: Interaction energies, vibrational frequencies, and classical thermodynamic and dynamical properties from clusters to liquid water and ice
• Determination of phase diagrams via computer simulation: Methodology and applications to water, electrolytes and proteins
• Advances in the experimental exploration of water's phase diagram
• Homogeneous ice nucleation evaluated for several water models
• Local order parameters for use in driving homogeneous ice nucleation with all-atom models of water
• The phase diagram of water at high pressures as obtained by computer simulations of the TIP4P/2005 model: the appearance of a plastic crystal phase
• Quantum contributions in the ice phases: the path to a new empirical model for water -- TIP4PQ/2005
• Direct path integral estimators for isotope fractionation ratios
• Configurational entropy of hydrogen-disordered ice polymorphs
• Extracting ice phases from liquid water: why a machine-learning water model generalizes so well