  The high temperature behaviour of graphene is studied by atomistic
simulations based on an accurate interatomic potential for carbon. We find that
clustering of Stone-Wales defects and formation of octagons are the first steps
in the process of melting which proceeds via the formation of carbon chains.
The molten state forms a three-dimensional network of entangled chains rather
than a simple liquid. The melting temperature estimated from the
two-dimensional Lindemann criterion and from extrapolation of our simulation
for different heating rates is about 4900 K.
