Coarse-grained Molecular Dynamics Models for Crystalline Solids at Finite Temperature

Atomistic models, such as molecular dynamics, have been very useful computational tools in many applications, especially where atomic-scale structures are crucial to the overall properties. A full atomistic model is often computationally intractable due to the huge number of degrees of freedom. The main objective of this project is to develop coarse-grained models so that computer simulations can be conducted at a much reduced cost. Rather than relying on empirical constitutive laws, this work aims to derive the coarse-scale model directly based on molecular dynamics using a projection formalism. As an application, the coarse-grained models will be applied to dislocation dynamics, to study the response of a solid system with a mixture of dislocations.

At the atomic scale, crystalline solids contain many defects of delicate structures, and the detailed configurations, e.g. the type of defects, orientations, and concentrations, are ultimately responsible for the mechanical properties of the material at the macroscopic scale. Atomistic models, such as molecular dynamics, directly take into account the interaction of the constituting atoms. The main challenge, however, is that such a system is usually too large to fit in any practical computation. In addition, it is not clear how macroscopic quantities of interest are related to the position of the atoms. This work offers a systematic approach to reduce the size of atomistic models, without compromising the accuracy. The reduced model will make it possible to simulate systems of realistic size, and provide valuable insight on the microscopic mechanism underlying many material processes.