Multiscale Modeling of Defects in Atomic Monolayers Undergoing Complex Bending Deformation

Thursday, August 10, 2017 - 10:00am - 10:45am
Vincent 215
Kaushik Dayal (Carnegie Mellon University)
We present a multiscale method for defects in low-dimensional atomic and molecular systems that undergo complex bending deformations with non-zero Gaussian curvature. Our technical strategy is based on a generalization of Objective Structures (OS); OS are a large class of nanostructures with symmetry properties that are rooted in frame-indifference. OS have many attractive features, e.g., a connection to group theory, potentially a fundamental basis in the structure of materials analogous to crystals, and so on. While OS have these attractive properties that make them valuable as a tool for multiscale modeling, they do not include extended nanostructures with Gaussian curvatures. Therefore, our technical strategy introduces a generalization of OS, that we term quasi-OS (qOS). qOS have the property that they can have Gaussian curvature, but recover the attractive properties of OS in certain key limits such as vanishing Gaussian curvature. We use qOS as a means to efficiently estimate energies and forces in large portions of the naostructure away from the defect, thereby enabling multiscale calculations for large systems. We apply the multiscale method to a problem involving defects and their interaction with imposed deformations, namely, the behavior of a dislocation in a graphene sheet. We find that the reduction in bending rigidity due to a single dislocation is about 40% in the configuration that we consider.