Diffusion dynamics of supercooled water modeled with the cage-jump motion and hydrogen-bond rearrangement

Abstract

The slow dynamics of glass-forming liquids is generally ascribed to the cage-jump motion. In the cage-jump picture, a molecule remains in a cage formed by neighboring molecules, and after a sufficiently long time, it jumps to escape from the original position by cage-breaking. The clarification of the cage-jump motion is therefore linked to unraveling the fundamental element of the slow dynamics. Here, we develop a cagejump model for the dynamics of supercooled water. The caged and jumping states of a water molecule are introduced with respect to the hydrogen-bond (H-bond) rearrangement process, and describe the motion in supercooled states. It is then demonstrated from the molecular dynamics simulation of the TIP4P/2005 model that the characteristic length and time scales of cage-jump motions provide a good description of the selfdiffusion constant that is determined in turn from the long-time behavior of the mean square displacement. Our cage-jump model thus enables to connect between H-bond dynamics and molecular diffusivity. arXiv:1903.06060v2 [cond-mat.soft]

Comparing Microscopic and Macroscopic Dynamics in a Paradigmatic Model of Glass-Forming Molecular Liquid

“…In the past few years, algorithms to characterize cage-jump events have been successfully developed, focusing either on fluctuations in single-particle trajectories [ 9 , 14 , 15 , 16 ], or on many-particles rearrangement [ 17 , 18 , 19 ], or on transitions in the energy landscape [ 20 , 21 ]. The statistics obtained through these algorithms, such as cage-duration and jump-length distributions, can then be used as input in simple models of glassy dynamics, like for example the Continuous Time Random Walk (CTRW) model [ 22 , 23 ].…”

Robustness of the Hydrogen Bond and Ion Pair Dynamics in Ionic Liquids to Different Parameters from the Reactive Flux Method

“…Molecular dynamics (MD) simulations which often were used to tackle thermodynamic − and transport − properties also have been shown to be a promising way to approach the topic of HBs. ,,,,− Recently, we analyzed ionic liquid hydrogen-bond dynamics with MD simulations based on the reactive flux approach − and presented therein an expansion of the concept to the dynamics of ions . In this work, we investigate the anion and temperature variations and test the boundaries of the method in terms of simulation parameters.…”

Water Diffusion Proceeds via a Hydrogen-Bond Jump Exchange Mechanism

“…We now briefly contrast this picture with prior jump descriptions of water translational diffusion. Prior studies 10,11,16,27 considered that water structural dynamics could be separated into a fast rattling motion within a local basin, for example formed by the surrounding 10 water molecules in the cage model, 27 and slower inter-basin jumps. However, our results in Fig.…”

“…Water diffusion has often been described with random walk and jump diffusion models involving elementary hops. − However, these models have only been used as effective descriptions, and the molecular mechanism of these elementary hops and their connection with H-bond rearrangements have not been characterized. In addition, the molecular parameters obtained from these effective models were often not consistent with other dynamical studies: for example, the inferred delays between successive hops − did not match any known time scale for the H-bond network dynamics.…”