Stone-Wales graphene: A two-dimensional carbon semimetal with magic stability

A two-dimensional carbon allotrope, Stone-Wales graphene, is identified in stochastic group and graph constrained searches and systematically investigated by first-principles calculations. Stone-Wales graphene consists of well-arranged Stone-Wales defects, and it can be constructed through a 90^∘ bond rotation in a √8×√8 supercell of graphene. Its calculated energy relative to graphene, +149 meV/atom, makes it more stable than the most competitive previously suggested graphene allotropes We find that Stone-Wales graphene (SW-graphene) based on a √8 supercell is more stable than those based on √9×√9,0.28em0ex√12×√12, and √13×√13 supercells, and is a ``magic size'' that can be further understood through a simple ``energy splitting and inversion'' model. The calculated vibrational properties and molecular dynamics of SW-graphene confirm that it is dynamically stable. The electronic structure shows SW-graphene is a semimetal with distorted, strongly anisotropic Dirac cones.