Predominantly pentagonal ice bilayers: energetics and self-assembly properties

Ice and gas hydrates exhibit extraordinary structural diversity, which is superimposed by exponential proton disorder caused by the ambiguous arrangement of hydrogen atoms (protons) in hydrogen bonds. In many water clusters and finite ice nanostructures, the relative energy variation due to proton disorder is much greater than in bulk samples. Two-layer ices are a separate class of water nanostructures, in which the variation in the stabilization energy is also large and, per water molecule, comparable with the heat of fusion of ice. An important feature of some bilayer ices is the presence of large cavities, which, in the presence of confining walls, allows them to be considered as frameworks of 2D clathrate hydrates. To study the stability of different ice bilayers, taking into account proton disorder, computer simulations were performed using the non-additive intermolecular potential AMOEBA. Emphasis was placed on bilayers whose individual layers predominantly form pentagonal rings. The factors determining the stability of bilayer ices were identified. The necessary topological condition for the assembly of planar 3-coordinated lattices and corresponding ice bilayers from individual fragments is established. Self-assembly methods that yield the most stable bilayer configurations are discussed.