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

PM Derlet, PHYSICAL REVIEW MATERIALS, 4, 125601 (2020).

DOI: 10.1103/PhysRevMaterials.4.125601

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 metallic 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. By introducing a modified radical Voronoi tessellation, which removes some ambiguity in how nearest-neighbor bonds are enumerated, it is found, that a large proportion (>95%) of local atomic environments follow the connectivity rules of the SU(2) topology 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 to analyze thermally activated structural excitations, revealing those high-energy/low- density/elastically soft regions not following the connectivity constraints are more likely to undergo structural rearrangement that often ends with the creation of new SU(2) local topology content. The work provides a new analysis tool to study the connectivity of developing structural motives characteristic of isotropic undercooled liquids, their transition to a glass, and subsequent glassy structural relaxation.

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