Diffusion anomaly and dynamic transitions in the Bell-Lavis water model

TL;DR

This study explores the dynamic and thermodynamic anomalies of the Bell-Lavis water model, revealing a fragile-to-strong diffusivity transition at low pressures and challenging the presumed link between dynamic transitions and criticality.

Contribution

It provides new insights into the dynamic behavior of the Bell-Lavis water model, especially regarding the relation between diffusivity anomalies and phase transitions.

Findings

Model exhibits anomalous diffusion within density anomalies.

Fragile-to-strong transition occurs at low pressures near the critical line.

No dynamic transition observed at higher densities crossing the critical line.

Abstract

In this paper we investigate the dynamic properties of the minimal Bell-Lavis (BL) water model and their relation to the thermodynamic anomalies. The Bell-Lavis model is defined on a triangular lattice in which water molecules are represented by particles with three symmetric bonding arms interacting through van der Waals and hydrogen bonds. We have studied the model diffusivity in different regions of the phase diagram through Monte Carlo simulations. Our results show that the model displays a region of anomalous diffusion which lies inside the region of anomalous density, englobed by the line of temperatures of maximum density (TMD). Further, we have found that the diffusivity undergoes a dynamic transition which may be classified as fragile-to-strong transition at the critical line only at low pressures. At higher densities, no dynamic transition is seen on crossing the critical line. Thus evidence from this study is that relation of dynamic transitions to criticality may be discarded.