Collineations of particles in the Kob-Andersen system

TL;DR

This study investigates long particle collineations in the Kob-Andersen system, revealing unexpected behavior below the crossover temperature and exploring their potential links to other structural features in supercooled liquids.

Contribution

It systematically analyzes long collineations in supercooled liquids and introduces a model connecting these structures with pair and angular density functions.

Findings

Number of collineations exceeds that of inherent structures below crossover temperature

A model accurately describes long collineations based on pair and angular densities

No clear connection found between collineations and disclination lines, low-energy clusters, or chain-like motions

Abstract

Numerous indications suggest that subtle changes occurring in the structures of liquids on supercooling are connected to the phenomenon of the glass transition and that detailed understanding of these changes is crucial for the development of new glasses with desired properties. J.D. Bernal in his 1962 Bakerian lecture, in particular, reported about an observation of approximately linear chains of several particles, referred to as collineations. He found that in the studied hard sphere system, these collineations can contain up to eight particles. Since then, the collineations of three particles have been discussed in many papers in the context of the splitting of the second peak in pair density functions of supercooled liquids and glasses. However, it appears that longer collineations involving more that three particles have not been systematically studied. Here, we report on our study of such collineations for the Kob-Andersen system of particles on cooling for the parent and inherent structures. Contrary to intuition, our findings reveal that below the potential energy landscape crossover temperature, the number of collineations in the parent structures can exceed that of the corresponding inherent structures. We also introduce a model that connects long collineations with the pair density and angular density distribution functions and demonstrate that this model describes long collineations quite well. The second part of the paper explores potential connections between collineations and: 1) the disclination lines associated with the geometric frustration approach, 2) low-energy clusters from the topological cluster classification approach, 3) chain-like cooperative motion of particles in low-temperature supercooled liquids. For the studied system, according to the used methods, no clear connection was found between collineations and these phenomena.