Orbital-Free DFT Simulations of Elastic Response and Tensile Yielding of Ultrathin [111] Al Nanowires

Elastic properties and mechanisms for tensile yielding of fcc Al nanowires are explored using orbital-free density functional theory. We quasistatically load ultrathin nanowires that have circular cross sections, diameters 1-8 nm, lengths up to similar to 20 nm, and axes along the [111] direction. We find that Young's modulus is roughly consistent for the nanowires and bulk Al but that the equilibrium interlayer spacing, elastic limit, and yield strength are diameter dependent. Plasticity is nucleated by 3-fold symmetric axial displacements of surface atoms for all nanowires examined. However, the nanowire with 4 nm diameter yields via partial slip before achieving the theoretical strength of bulk Al, while the 1 and 2 nm nanowires yield via amorphous mechanisms, above or near the theoretical strength. These results give new insight into the plastic yielding mechanisms of ultrathin fcc nanowires with edge-free cross sections and [111] orientation.