Relation between Rotational and Translational Dynamic Heterogeneities in Water

TL;DR

This study uses molecular dynamics simulations to explore the relationship between rotational and translational dynamic heterogeneities in water, revealing their spatial correlation and temperature dependence.

Contribution

It demonstrates the strong correlation between rotational and translational heterogeneities in water and analyzes their size, behavior, and physical connection.

Findings

Rotational heterogeneities form clusters that vary with temperature.

Position of rotational and translational heterogeneities are strongly correlated.

Fraction of molecules with both heterogeneities increases as temperature decreases.

Abstract

We use molecular dynamics simulations to probe the rotational dynamics of the SPC/E model of water for a range of temperatures down to 200 K, 13 K above to the mode coupling temperature. We find that rotational dynamics is spatially heterogeneous, i.e., there are clusters of molecules that rotate significantly more than the average for a given time interval, and we study the size and the temporal behavior of these clusters. We find that the position of a rotational heterogeneity is strongly correlated with the position of a translational heterogeneity, and that the fraction of molecules belonging to both kinds of heterogeneities increases with decreasing temperature. We further find that although the two types of heterogeneities are not identical, they are related to the same physical picture.