Emergence of rigid Polycrystals from atomistic Systems with Heitmann-Radin sticky disk energy

TL;DR

This paper studies how rigid polycrystalline structures emerge from atomistic systems with sticky disk interactions, using mathematical tools to connect microscopic configurations to continuum grain boundary energies.

Contribution

It provides a rigorous characterization of the asymptotic behavior of atomistic configurations and derives a local continuum energy describing grain boundaries without assuming a reference lattice.

Findings

Effective continuum energy is concentrated on grain boundaries.

Surface energy density depends on orientation, translation misfit, and interface normal.

Boundary layers near cracks are energetically unfavorable in brittle setups.

Abstract

We investigate the emergence of rigid polycrystalline structures from atomistic particle systems. The atomic interaction is governed by a suitably normalized pair interaction energy, where the `sticky disk' interaction potential models the atoms as hard spheres that interact when they are tangential. The discrete energy is frame invariant and no underlying reference lattice on the atomistic configurations is assumed. By means of $\Gamma$-convergence, we characterize the asymptotic behavior of configurations with finite surface energy scaling in the infinite particle limit. The effective continuum theory is described in terms of a piecewise constant field delineating the local orientation and micro-translation of the configuration. The limiting energy is local and concentrated on the grain boundaries, i.e., on the boundaries of the zones where the underlying microscopic configuration has constant parameters. The corresponding surface energy density depends on the relative orientation of the two grains, their microscopic translation misfit, and the normal to the interface. We further provide a fine analysis of the surface energies at grain boundaries both for vacuum-solid and solid-solid phase transitions. The latter relies fundamentally on a structure result for grain boundaries showing that due to the extremely brittle setup interpolating boundary layers near cracks are energetically not favorable.