Aspects of the percolation process for hydrogen-bond networks in water

Abstract

Sets of configurations selected from three molecular dynamics simulations for liquid water have been analyzed for the distribution of hydrogen‐bond clusters. Two simulations correspond to water at 1 g cm⁻³, while the third corresponds to highly compressed water at 1.346 g cm⁻³. An energy criterion was adopted for existence of a hydrogen‐bond between two molecules. As the cutoff value for bonding increases (becomes more permissive), a bond percolation threshold is encountered at which initially disconnected clusters suddenly produce a large space‐filling random network. At least for the model studied, any chemically reasonable definition of ’’hydrogen‐bond’’ leads to this globally connected structure though a few disconnected fragments inhabit its interior. Although some polygonal closures can exist, the critical percolation threshold is apparently well predicted by Flory’s theory of the gel point for dendritic polymerization.