Stability of dislocation defect with two pentagon-heptagon pairs in graphene

The stability of a dislocation defect with two pentagon-heptagon (5-7) pairs in a graphene layer is investigated within first-principles density-functional theory scheme. It is found that the structure of the dislocation defect with two 5-7 pairs becomes more stable than a local haeckelite structure which is composed of defect units of three pentagons and three heptagons (555-777 defect) when the number of vacancy units is ten and over. The simulation study of scanning tunneling microscopy reveals that the 5-7 pair defects perturb the wave functions of electrons near Fermi level to produce the (root 3x root 3)R30(0): a superlattice pattern.