Topological Identification Criteria, Stability, and Relevance of Pentagonal Nanochannels in Amorphous Ice.

Considering the potential importance of pentagonal nanochannels (PNCs) in determining the structure of the amorphous ice, we introduce topological criteria to identify the PNCs with an optimal fivefold symmetric environment. The basic building block in our criteria, termed as a bicyclo octamer, is an axisymmetric cluster formed by combination of three 6-membered boat-shaped rings. This bicyclo octamer unit serves as a seamless interface of the PNCs with cubic-hexagonal stacking patterns of the amorphous ice.

Increase in local crystalline order across the limit of stability leads to cubic-hexagonal stacking in supercooled monatomic (mW) water.

At the limit of stability of a supercooled tetrahedral liquid modeled by monatomic (mW) water potential, it was recently shown that relaxation occurs across a unique value of per particle potential energy ( ), which corresponds to a dynamical (non-stationary) condition of Gibbs free energy function (, , , ): [(/)/ = 0] and [(/)/ ≠ 0]. In this work, we explore the inherent structures responsible for the formation of the amorphous states through such a mechanism of relaxation of mW liquid. We first identify 6-member boat and chair shaped rings using a criterion based on the internal dihedral angles.