Spontaneous and induced dynamic correlations in glass-formers II: Model calculations and comparison to numerical simulations

TL;DR

This paper compares theoretical predictions from mode-coupling theory and kinetically constrained models with numerical simulations to understand multi-point correlation functions in glass-forming liquids, revealing strengths and limitations of these models.

Contribution

It provides a detailed comparison of MCT and KCM predictions with simulations, clarifying their applicability to fragile and strong glass formers.

Findings

MCT accurately predicts dynamics in fragile glass-formers.

MCT predictions do not hold for strong glass-formers.

KCMs offer insights but face unresolved questions in supercooled liquids.

Abstract

We study in detail the predictions of various theoretical approaches, in particular mode-coupling theory (MCT) and kinetically constrained models (KCMs), concerning the time, temperature, and wavevector dependence of multi-point correlation functions that quantify the strength of both induced and spontaneous dynamical fluctuations. We also discuss the precise predictions of MCT concerning the statistical ensemble and microscopic dynamics dependence of these multi-point correlation functions. These predictions are compared to simulations of model fragile and strong glass-forming liquids. Overall, MCT fares quite well in the fragile case, in particular explaining the observed crucial role of the statistical ensemble and microscopic dynamics, while MCT predictions do not seem to hold in the strong case. KCMs provide a simplified framework for understanding how these multi-point correlation functions may encode dynamic correlations in glassy materials. However, our analysis highlights important unresolved questions concerning the application of KCMs to supercooled liquids.