Hierarchical Lattice Models of Hydrogen Bond Networks in Water

Rahul Dandekar, Ali A. Hassanali

Published 2017-09-25Version 1

Lattice models have been extensively used to explore and understand the complex physics of the phase diagram of water. In this work, we develop models that are built \emph{bottom up}, based on microscopic information coming from atomistic simulations. These models are essentially graph-based models for the hydrogen bond network of water. The phase diagram of these models confirms the singularity-free scenario previously proposed by Sastry and co-workers (Sastry et al, PRE 53, 6144 (1996)). We examine the pair-distribution functions on the lattice and show that the correlations and clustering of local-coordination defects around tetrahedral waters observed in the atomistic simulations, can be rationalized by the simple entropic models. Orientational correlations between bonds are also determined and find them to be longer range than those where directionality is neglected. We also determine the directional correlations within closed loops and show that the patterns of water wires within these structures are also consistent with previous atomistic simulations. Our models reproduce some important anomalies such as the density maximum and compressibility minimum the exact details of which, are sensitive to the presence of coordination defects in the network.