(a) Lattice structure of ideal graphene with the lattice constant a = 1.42 Å and the primitive vectors a₁ and a₂. The primitive cell contains two kinds of atoms labeled by A and B. (b) A supercell contains 112 atoms, with two basis vectors b₁ = 12ai and along the armchair and zigzag directions, respectively; (c) Single vacancy V₁(5-9); (d) Double vacancy V₂(5-8-5). (e) Triple vacancy V₃(5-10-5). (f) Quadruple vacancy V₄(555-9). The dashed lines and the open circles represent the missing bonds and carbon atoms, respectively.