  We study the stability and evolution of various elastic defects in a flat
graphene sheet and the electronic properties of the most stable configurations.
Two types of dislocations are found to be stable: "glide" dislocations
consisting of heptagon-pentagon pairs, and "shuffle" dislocations, an octagon
with a dangling bond. Unlike the most studied case of carbon nanotubes, Stone
Wales defects are unstable in the planar graphene sheet. Similar defects in
which one of the pentagon-heptagon pairs is displaced vertically with respect
to the other one are found to be dynamically stable. Shuffle dislocations will
give rise to local magnetic moments that can provide an alternative route to
magnetism in graphene.
