Ultrastable states in Jammed Packings: Characterization and Construction

Jammed packings serve as model systems for the structure and mechanical behavior of disordered assemblies of particles, from colloids to glassy solids. A recent focus has been on the detection and characterization of structures with unusual, exceptional properties such as strongly enhanced stability with respect to imposed strain. In simulations of overjammed polydisperse 2D packings of soft disks, we identify such rare, ultrastable states via an order parameter that quantifies the closeness of the structure to a sterically optimal packing, simultaneously correlating these states with low-energy inherent structures.

Moreover, we develop a novel particle swap algorithm that constructs such ultrastable states much faster than traditional swap approaches, by simultaneously exchanging the positions of all particles guided by the order parameter. This technique can be extended to systems with different volume fraction or different interaction potential, and becomes more efficient as system size increases. In facilitating the study of these exceptional microstates, which are not commonly produced by conventional simulations, this work opens up a more complete view of the intricate energy landscape of disordered packings and, by extension, of a variety of modern complex materials.

Reference: Kim S, Hilgenfeldt S. Structural Measures as Guides to Ultrastable States in Overjammed Packings. Phys. Rev. Lett. 129:168001 (2022).