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The objective of this research is to use atomistic simulations to investigate dislocation nucleationfrom asymmetric tilt grain boundaries in FCC copper and aluminum. We use a 3D periodicbicrystal configuration to investigate how grain boundary degrees of freedom impact both theboundary structure and dislocation nucleation in symmetric and asymmetric tilt boundaries.Simulation results show that dislocation nucleation from asymmetric tilt grain boundaries requiresunderstanding of the structure and faceting of these boundaries. Deformation simulations of singlecrystals and grain boundaries under uniaxial tension and compression show entirely differentnucleation mechanisms, i.e., nucleation of full dislocations in copper from the grain boundaryunder compression. Analysis of the resolved stresses shows that the resolved stress normal to theslip plane on which the dislocation nucleates plays an integral role in dislocation nucleation forboth single crystals and interfaces.