First-Principles Study of Graphene and Carbon Nanotubes Functionalized with Benzyne

We applied ab initio computational methods based on density functional theory to study the properties of graphene and single-walled carbon nanotubes functionalized with benzyne. The calculations were carried out using the SIESTA electronic structure code combined with the generalized gradient approximation for the exchange correlation functional. Our study showed that the reaction of cycloaddition of benzyne to pristine graphene was exothermic with the possibility of formation of both [2 + 2] and [4 + 2] reaction products. The binding energies of benzyne molecules attached to semiconducting zigzag and metallic armchair nanotubes were found to be inversely proportional to the nanotube diameter. The linear fits of the binding energies between benzyne and carbon nanotubes extrapolated to the zero curvature limit were in good agreement with the binding energies of benzyne attached to graphene. Our calculations demonstrated that the cycloaddition of benzyne could open up a nonzero gap between the valence and conduction bands of graphene and metallic carbon nanotubes. The value of the band gap was significantly affected by the geometry of benzyne attachment and by the choice of the supercell.