Universality of liquid dynamics

TL;DR

This paper explores the universal relationship between structural relaxation and diffusion in liquids, attributing it to a dominant length scale linked to structural correlations, and models it using independent random walkers.

Contribution

It introduces a new measure of structural relaxation and explains the universality of liquid dynamics through a simple random walk model.

Findings

The universal relation is caused by a single dominant length scale.

Structural correlations impose a length scale related to de Gennes narrowing.

A model of independent random walkers captures the relation effectively.

Abstract

We investigate the origin of the Stokes-Einstein relation in liquids. The hard-sphere dynamics is analyzed using a new measure of structural relaxation - the minimum Euclidean distance between configurations of particles. It is shown that the universal relation between the structural relaxation and diffusion in liquids is caused by the existence of one dominating length scale imposed by the structural correlations and associated with de Gennes narrowing. We demonstrate that this relation can be described by a model of independent random walkers under the single-occupancy constraint.