Electronic structure of isomeric graphene nanoflakes

Abstract

A comparative theoretical study of graphene nanoflakes (NFs) and isomeric NFs based on two different graphene allotropes has been carried out using hybrid density functional theory and complete active space calculations. Two graphene allotropes H1 and H2 consisted of fused azulene rings were found to be less stable compared to isomeric graphene NFs at all theoretical levels. H1 and H2 have closed shell singlet ground state independently on their size and strong bond length alternation. For all types of NFs, the evolution of the ionization potential (IP), electron affinity (EA) and band gap (Eg) with size is similar. IP and Eg drop and EA increases with NF size. H1 and H2 show lower IPs and Egs and higher EAs compared to the corresponding graphene NF of the same size. However, IPs, Egs and EAs converge with size for all three types of the NF becoming nearly identical for the largest representatives of H1, H2 and graphene NF. H1 and H2 types of NF have a non-uniform distribution of the electron density across the NF, unlike graphene systems, which makes them promising candidates for regioselective chemical modification.