Twisted bilayer Ice as a new class of hydrogen-bonding moiré materials.

Twisted bilayer van der Waals materials have become a transformative framework for the design of quantum and electronic devices, yet their counterparts, the twisted bilayer non-van der Waals materials, remain largely unexplored. Here, we report the first molecular-dynamics simulation evidence of the spontaneous formation of twisted bilayer ice with moiré patterns. Unlike the twisted bilayer van der Waals materials which can be produced by manually twisting one monolayer relative to another, twisted-bilayer-ice formation hinges on the structural adaptability of hydrogen bonds to achieve thermodynamic stability. First-principles molecular-dynamics simulations confirm the thermal stability of the twisted bilayer ice with two different moiré patterns, one with commensurate twist angle of 21.8° and another 27.8°. A phase diagram illustrates the stability region of twisted bilayer ice, providing guidance for future experimental validation. This work not only expands the family of two-dimensional ices but also advances the notion of twisted bilayer hydrogen-bonding materials, thereby offering opportunities to investigate emergent properties and potential applications of twisted bilayer non-van der Waals materials.