Correlated disorder in a well relaxed model binary glass through a local SU(2) bonding topology

TL;DR

This study applies a local bonding constraint theory to a well-relaxed binary Lennard-Jones glass, revealing that most atomic environments follow SU(2) topology, and defect networks influence structural rearrangements.

Contribution

It demonstrates the applicability of Nelson's SU(2) bonding topology theory to a model binary glass, linking defect networks to structural relaxation mechanisms.

Findings

Over 95% of local environments follow SU(2) topology.

Low energy structures have fewer bond-length frustrations.

Defect networks correlate with regions prone to structural rearrangements.

Abstract

A quantitative understanding of the microscopic constraints which underlie a well relaxed glassy structure is the key to developing a microscopic theory of structural evolution and plasticity for the amorphous solid. Here we demonstrate the applicability of one such theory of local bonding constraints developed by D. R. Nelson [Phys. Rev. B 28, 5515 (1983)], for a model binary Lennard-Jones glass structure that has undergone an isothermal annealing simulation spanning over 10 micro-seconds of physical simulation time. By introducing a modified radical Voronoi tessellation which removes some ambiguity in how nearest neighbour bonds are enumerated, it is found, that a large proportion ($>95\%$) of local atomic environments follow the connectivity rules of the SU(2) topology of Nelson's work resulting in a dense network of disclination lines characterizing the defect bonds. Furthermore, it is numerically shown that a low energy glass structure corresponds to a reduced level of bond-length frustration and thus a minimally defected bond-defect network. It is then demonstrated that such a defect network provides a framework in which to analyse thermally-activated structural excitations, revealing those high-energy/low-density regions not following the connectivity constraints are more likely to undergo structural rearrangement that often results in a local relaxation that ends with the creation of new SU(2) local topology content.