  The Bernal-Fowler ice rules stipulate that each water molecule in an ice
crystal should form four hydrogen bonds. However, in extreme or constrained
conditions, the arrangement of water molecules deviates from conventional ice
rules, resulting in properties significantly different from bulk water. In this
study, we employ machine learning-driven first-principles simulations to
identify a new stabilization mechanism in nanoconfined ice phases beyond
conventional ice rules. Instead of forming four hydrogen bonds, nanoconfined
crystalline ice can form a quasi-one-dimensional hydrogen-bonded structure that
exhibits only two hydrogen bonds per water molecule. These structures consist
of strongly hydrogen-bonded linear chains of water molecules that zig-zag along
one dimension, stabilized by van der Waals interactions that stack these chains
along the other dimension. The unusual interplay of hydrogen bonding and van
der Waals interactions in nanoconfined ice results in atypical proton behavior
such as potential ferroelectric behavior, low dielectric response, and
long-range proton dynamics.
