  Due to the large free surface and strong anisotropy, the mechanical property
of nanowire differs from its bulk counterpart. In this paper, the strong
dependence of NW's strength on its surface orientation is revealed, and two
modes of dislocation nucleation have been identified: the corner nucleation and
the surface nucleation. The activation energy and activation volume of surface
nucleation are much larger than those of the corner nucleation. The
intersection line between lateral surface and {111}-type slip plane causes the
discrepancy of the nucleation modes for the first dislocation.
