Structural Signatures of Vitrification in Hard Core Fluids

TL;DR

This paper uses computer simulations to analyze free volume measures in hard sphere fluids, revealing that vitrification is a geometrical phenomenon linked to cavity sizes and caging onset.

Contribution

It introduces free volume measures like cavity and rattle sizes to identify vitrification and caging onset in hard core fluids, emphasizing a geometric perspective.

Findings

Cavity and rattle sizes extrapolate to zero at the random close packed density.

Caging begins when cavities cluster, indicating the onset of vitrification.

Local free volume measures can predict liquid-like dynamics and vitrification.

Abstract

Computer simulations of hard spheres and disks are used to estimate the most probable cavity size, $\xi_{\rm cavity}$, and a ``rattle'' size, $\xi_{\rm rattle}$, over which a particle can translate holding all other particles fixed. Both of these measures of free volume appear to extrapolate to zero at the random close packed density, $\rho_{\rm rcp}$, close to the density where extrapolations of the viscosity diverge. We also identify the onset of caging as the density at which cavities cluster. These results suggest that vitrification in hard core fluids can be viewed as a geometrical phenomenon, and that {\em local} free volume measures can identify the location of the onset of liquid-like dynamics, the complex dynamics of caged liquids, and vitrification.