Quasicontinuum models of interfacial structure and deformation V. B. Shenoy, R. Miller, E. B. Tadmor, R. Phillips and M. Ortiz Physical Review Letters, 80, 742-745 (1998). ABSTRACT Microscopic models of the interaction between grain boundaries (GBs) and both dislocations and cracks are of importance in understanding the role of microstructure in altering the mechanical properties of a material. A recently developed mixed atomistic and continuum method is reformulated to allow for the examination of the interactions between GBs, dislocations, and cracks. These calculations elucidate plausible microscopic mechanisms for these defect interactions and allow for the quantitative evaluation of critical parameters such as the force needed to induce GB migration.