Materials simulations at the atom-continuum interface: Dislocation mobility and notched fracture initiation.

摘要

We have solved three problems with a common theme of interfacing atomistic models with continuum models. The first is measuring the Peierls barrier for dislocation glide in a two dimensional material. The key features of this work are (1) efficient extrapolation of the infinite system limit from small simulations, through the use of multipole relaxation at the atom-continuum interface, and (2) the representation of the dependence on external parameters (in this case applied stress) in a compact way using a physically motivated functional form. The second problem is the initiation of fracture at sharp notches in single crystal silicon, a problem of current experimental interest in microfabrication. It is found that when expressed in atomic-scale units the critical stress intensity factor is almost independent of notch opening angle, as long as the interatomic potential does, in fact, produce brittle fracture. The third problem is the challenge of incorporating atomistic simulations in an adaptive manner in large scale continuum (finite element) simulations. Our method involves embedding such simulations within elements in an overlapping sense, and avoids some of the complexity associated with alternative methods. We solve these three problems through the development of a flexible, modern, powerful molecular dynamics package, known as DigitalMaterial. We describe the design of the software, which is fully object-oriented. What makes this package different from others is the use of a component-based approach based on software engineering methods known as Design Patterns. The interfaces for these components are very clearly defined, allowing components to be interoperable and to be easily driven from a high level scripting environment.