Cage rattling does not correlate with the local geometry in molecular liquids

TL;DR

This study uses molecular dynamics simulations to show that local geometric features do not predict particle motion in molecular liquids, indicating that cage rattling is a collective process involving more than just immediate neighbors.

Contribution

It demonstrates that local Voronoi geometry poorly correlates with particle dynamics, highlighting the non-local nature of cage rattling in molecular liquids.

Findings

Poor correlation between Voronoi geometry and particle displacement.

Cage rattling involves collective motion beyond nearest neighbors.

Monomers exhibit similar displacement distributions despite local geometric differences.

Abstract

Molecular-dynamics simulations of a liquid of short linear molecules have been performed to investigate the correlation between the particle dynamics in the cage of the neighbors and the local geometry. The latter is characterized in terms of the size and the asphericity of the Voronoi polyhedra. The correlation is found to be poor. In particular, in spite of the different Voronoi volume around the end and the inner monomers of a molecule, all the monomers exhibit coinciding displacement distribution when they are caged (as well as at longer times during the structural relaxation). It is concluded that the fast dynamics during the cage trapping is a non-local collective process involving monomers beyond the nearest neighbours.