The collective burst mechanism of angular jumps in liquid water

The collective nature of reorientational dynamics in water remains poorly understood. Here, the authors show that large angular fluctuations require a highly cooperative dynamics involving correlated motion of many water molecules in the hydrogen-bond network that form spatially connected clusters. Understanding the microscopic origins of collective reorientational motions in aqueous systems requires techniques that allow us to reach beyond our chemical imagination. Herein, we elucidate a mechanism using a protocol that automatically detects abrupt motions in reorientational dynamics, showing that large angular jumps in liquid water involve highly cooperative orchestrated motions. Our automatized detection of angular fluctuations, unravels a heterogeneity in the type of angular jumps occurring concertedly in the system. We show that large orientational motions require a highly collective dynamical process involving correlated motion of many water molecules in the hydrogen-bond network that form spatially connected clusters going beyond the local angular jump mechanism. This phenomenon is rooted in the collective fluctuations of the network topology which results in the creation of defects in waves on the THz timescale. The mechanism we propose involves a cascade of hydrogen-bond fluctuations underlying angular jumps and provides new insights into the current localized picture of angular jumps, and its wide use in the interpretations of numerous spectroscopies as well in reorientational dynamics of water near biological and inorganic systems. The role of finite size effects, as well as of the chosen water model, on the collective reorientation is also elucidated.

Automated summary

In this study, the authors investigate the collective nature of reorientational dynamics in water. They find that large angular fluctuations involve a highly cooperative dynamics of many water molecules in the hydrogen-bond network. They propose a mechanism involving a cascade of hydrogen-bond fluctuations underlying angular jumps, providing new insights into the interpretation of spectroscopies and reorientational dynamics of water.