Atomic structure and energetics of large vacancies in graphene
  We present a computational study on the topology, energetics and structural deformations for a large number of experimentally observed defect configurations in graphene. We find that both the number of lost hexagonal carbon rings and introduced non-hexagonal rings increase linearly as a function of the vacancy order (number of missing atoms). The formation energies of the defects increase by about 2.2 eV per missing atom after an initial offset, establishing these defects as the lowest energy vacancy configurations studied in graphene to date. In addition, we find that even small point defects, which have been until now assumed flat, cause graphene to bend out of plane when not restricted into prohibitively confined geometries. This effect reaches to relative long distances even for some of the smallest defects, significantly reducing the stress otherwise imposed on the surrounding lattice. 
Jani Kotakoski, Franz R. Eder, Jannik C. Meyer
cond-mat.mtrl-sci