Size-dependent elasticity of nanowires: Nonlinear effects

We employ a molecular statics approach based on embedded-atom-method interatomic potentials to study the elasticity of copper nanowires along [001], [110], and [111] crystallographic directions. Self-consistent comparison with the bulk response clearly shows that the overall nanowire elasticity is primarily due to nonlinear response of the nanowire core. While the surface-stress-induced surface elasticity modifies the behavior for ultrathin nanowires, their contribution is always considerably smaller than that due to nonlinear elasticity of the nanowire core. More importantly, for all three orientations, the surface is softer than an equivalently strained bulk, and the overall nanowire softening or stiffening is determined by orientation-dependent core elasticity.