  Stone-Wales (SW) defects, analogous to dislocations in crystals, play an
important role in mechanical behavior of $sp^2$-bonded carbon based materials.
Here, we show using first-principles calculations that a marked anisotropy in
the interaction among the SW defects has interesting consequences when such
defects are present near the edges of a graphene nano-ribbon: depending on
their orientation with respect to edge, they result in compressive or tensile
stress, and the former is responsible to depression or warping of the graphene
nano-ribbon. Such warping results in delocalization of electrons in the defect
states.
