Structural and electronic properties of graphene nanoflakes

The structures, cohesive energies, and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps of graphene nanoflakes and corresponding polycyclic aromatic hydrocarbons for a large variety of size and topology are investigated at the density-functional-based tight-binding level. Polyacenelike and honeycomblike graphene nanoflakes were chosen as the topological limit structures. The influence of unsaturated edge atoms and dangling bonds on the stability is discussed. Our survey shows a linear trend for the cohesive energy as function of N_s/N (N -total number of atoms and N_s is number of edge atoms). For the HOMO-LUMO gap the trends are more complex and include also the topology of the edges.