How coupled elementary units determine the dynamics of macroscopic glass-forming systems

TL;DR

This study explores how the properties of elementary units and their couplings influence the dynamics of glass-forming systems, revealing that local potential energy landscape parameters govern microscopic behavior while macroscopic relaxation exhibits finite size effects.

Contribution

It introduces a coupled landscape model that links elementary system dynamics to macroscopic behavior, highlighting the role of coupling strength near the glass transition.

Findings

Small system dynamics are well described by PEL parameters.

Large and small systems have similar diffusivities.

Structural relaxation time shows finite size effects.

Abstract

We investigate the dynamics of a binary mixture Lennard-Jones system of different system sizes with respect to the importance of the properties of the underlying potential energy landscape (PEL). We show that the dynamics of small systems can be very well described within the continuous time random walk formalism, which is determined solely by PEL parameters. Finite size analysis shows that the diffusivity of large and small systems are very similar. This suggests that the PEL parameters of the small system also determine the local dynamics in large systems. The structural relaxation time, however, displays significant finite size effects. Furthermore, using a non-equilibrium configuration of a large system, we find that causal connections exist between close-by regions of the system. These findings can be described by the coupled landscape model for which a macroscopic system is described by a superposition of elementary systems each described by its PEL. A minimum coupling is introduced which accounts for the finite size behavior. The coupling strength, as the single adjustable parameter, becomes smaller closer to the glass transition.