Effects of size on the structure and the electronic properties of graphene nanoribbons

In view of the current interest in graphene, especially graphene nanoribbons (GNRs), we carried out investigations using the molecular orbital cluster approach to find suitable models for use in simulations involving GNRs. Two types of nanoribbons were modeled, namely armchair- and zigzag-edged GNRs. We used four properties in determining the suitable models: molecular orbitals, spin densities, charges, and bond lengths. Among these criteria, it was found that size has a highly prominent effect on the molecular orbitals and bond lengths. The results show that models of sizes C126H32 and C110H30 are needed to represent the electronic and structural properties of infinite zigzag-edged and armchair-edged GNRs.