Quasi-continuum Reduction of Field Theories and Energetics of Defects in Aluminum.

[摘要] Defects strongly govern the formation of microstructure in crystalline materials and thus their material properties. Accurate study of defect energetics requires numerical techniques capable of handling a wide range of length scales from the angstrom to the micro-scale by resolution of short-ranged complex atomic re-arrangements at the defect core and long-ranged elastic distortions of the lattice in bulk. We use a three pronged approach to attempt to solve this problem: (a) Orbital Free Density Functional Theory, a fast yet chemically accurate physical model valid for metals with a valence electron density close to a free electron gas (e.g Al, Mg). (b) A real space formulation and a finite element based implementation to naturally couple quantum mechanics with continuum mechanics (c) A coarse grained model that removes cell size restrictions on simulations, thus providing capability to handle millions of atoms. We use this technique to study the defect-core and energetics of an edge dislocation in Aluminum. Our results suggest that the core-size – region with significant contribution of electronic effects to defect energetics – is around ten times the magnitude of the Burgers vector, which is much larger than core-sizes used in continuum studies. The computed core-structure, representing two Shockley partials, is consistent with other electronic structure and atomistic studies. Interestingly, our study indicates that the core-energy of an edge dislocation has a significant and a highly non-linear response to external macroscopic strains. From this core-energy dependence on macroscopic strains, we infer that interactions between dislocations involve an additional short-ranged force beyond the traditional Peach-Koehler force, and that this force is significant in regions of in-homogenous deformations.

[发布机构] University of Michigan

[效力级别] Orbital Free Density Functional Theory

[关键词] Quasi Continuum Method;Orbital Free Density Functional Theory;Defect Energetics;Mechanical Engineering;Engineering;Mechanical Engineering and Scientific Computing