Dynamics in inhomogeneous liquids and glasses via the test particle limit

TL;DR

This paper presents a dynamical density functional theory approach to analyze the van Hove correlation functions in inhomogeneous liquids and glasses, revealing insights into glass formation and particle mobility in confined systems.

Contribution

It introduces a novel interpretation of the van Hove functions as density distributions in a binary mixture, validated by simulations, and explores the energy landscape and mobility in dense and confined systems.

Findings

Quantitative agreement with Brownian dynamics simulations.

Identification of a free energy barrier related to glass formation.

Oscillations in barrier height correlate with local density in confined systems.

Abstract

We show that one may view the self and the distinct part of the van Hove dynamic correlation function of a simple fluid as the one-body density distributions of a binary mixture that evolve in time according to dynamical density functional theory. For a test case of soft core Brownian particles the theory yields results for the van Hove function that agree quantitatively with those of our Brownian dynamics computer simulations. At sufficiently high densities the free energy landscape underlying the dynamics exhibits a barrier as a function of the mean particle displacement, shedding new light on the nature of glass formation. For hard spheres confined between parallel planar walls the barrier height oscillates in-phase with the local density, implying that the mobility is maximal between layers, which should be experimentally observable in confined colloidal dispersions.