Polycyclic aromatic hydrocarbons as finite size models of graphene and graphene nanoribbons: Enhanced electron density edge effect

Highlights: ► It establishes existence of an edge effect in graphene and graphene nanoribbons. ► This edge effect is called enhanced electron density edge effect. ► Various results of previous studies can be explained using this edge effect. - Abstract: Distinct edge effects on physical and chemical properties are known to exist in graphene and graphene nanoribbons (GNRs). The present study provides a clue to understand the origin of these effects in terms of electron density distribution. Continuous electron density, molecular electrostatic potential and net charges obtained using density functional theory in several polycyclic aromatic hydrocarbons (PAHs) taken as finite size models of graphene and GNRs are analyzed. Electron density is found to be enhanced at the edges in comparison to those in the other parts of several PAHs and a similar distribution is also shown by spin densities in triplet ground states. Electron density is enhanced even at the hydrogen passivated internal edges created by removing carbon atoms of an inner benzene ring. Various experimental observations relating to distinct properties of edges of graphene and GNRs can be explained on the basis of the enhanced electron density edge effect.