A dual-space classification scheme of spatial heterogeneities in 2D monatomic supercooled liquids

TL;DR

This paper introduces a dual-space classification method using PCA and Gaussian Mixture clustering on weighted coordination numbers to identify and analyze spatial heterogeneities in supercooled liquids, revealing phase separation behavior.

Contribution

A novel dual-space classification scheme combining structural and configurational analysis to identify nano-domains in supercooled liquids.

Findings

Domains are consistent in structural and configurational spaces.

Heterogeneous dynamics are observed within identified domains.

Order parameter correlation follows non-conserved scaling law.

Abstract

Understanding the physics of supercooled liquids near glassy transition remains one of the major challenges in condensed matter science. There has been long recognized that supercooled liquids have spatially dynamical heterogeneity whose dynamics in some regions of the sample could potentially be orders of magnitude faster than the dynamics in other regions only a few nanometers away. However, to identify such domain structures both structurally and configurationally in a consistent fashion and the connection between structures and dynamics remains elusive. A new approach to classify these spatial heterogeneities of supercooled liquids is developed. Using average weighted coordination numbers (WCNs) of particles as features for the Principle Component Analysis (PCA) and Gaussian Mixture (GM) clustering, a representation of the feature space to perform GM clustering is constructed after applying PCA to WCNs. Nano-domains or aggregated clusters are found in configurational (real) space by direct mapping the identities of clusters in the feature (structural) space with some classification uncertainties. These uncertainties can be improved by a co-learning strategy to transmit information between the structural space and configurational space iteratively until convergence. The domains are indeed found to be remarkably consistent in both spaces over long times as well as measured to have heterogeneous dynamics. Using such a classification scheme the order parameter time correlation function follows the non-conserved order parameter scaling law, which indicates that such domains are the result of liquid-liquid phase separation after quenching.