  A nano-stitching method is proposed and investigated to modify graphene
bilayers. Based this method, four types of low energy carbon allotropes,
"wormhole graphene" allotropoes, are obtained and their structures, stabilities
and electronic properties are investigated using first principles methods. We
find that all of these wormhole graphene allotropoes are more favorable than
graphdiyne and dynamically stable. Similar to carbon nanotubes and fullerences,
these graphene allotropes are expected to act as two-dimensional periodic
nano-capsules for encapsulating magnetic atoms or functional clusters for a
variety of applications.
