Simulations of H₂O Solid, Liquid, and Clusters, with an Emphasis on Ferroelectric Ordering Transition in Hexagonal Ice

Simulations are presented of H2O ice, liquid, and clusters (H2O)n n ≤ 7. The first part is devoted to orientational energetics of ice. Ordinary hexagonal ice is orientationally disordered; a transition to an ordered form (ice XI) can be induced at 72 K. The recently demonstrated ferroelectric structure of ice XI (Jackson, S. M.; Wield, V. M.; Whitworth, R. W.; Oguro, M.; Wilson, C. J. Phys. Chem. B 1997, 101, 6142) seems to contradict our understanding of H2O···H2O interactions. A polarizable water potential is proposed that accounts qualitatively for the existence of ferroelectric ice XI; its crucial ingredient is the location of the polarizability center. This potential is then tested in classical trajectory simulations of water structure, energetics, self-diffusion, and dielectric constant. Cluster energetics and rotational constants are calculated using the rigid body diffusion Monte Carlo technique.