Interaction of aluminum dimer with defective graphene

In the present work, density functional theory (DFT) calculations using cluster and slab models were performed in order to study the adsorption of Al dimer on a monovacancy of graphene. With cluster models, two different approaches were considered for the exchange and correlation functional; namely, the Perdew, Burke and Ernzerhof (PBE) and the Becke, 3-parameter, Lee-Yang-Parr (B3LYP) functionals. Under the slab approximation only PBE was employed. The geometry where two Al atoms are simultaneously adsorbed on both sides of a monovacancy (H3-H3) is the most stable thermodynamically, followed by the structure in which one Al atom resides over the center of a vacancy and the other makes a bridge between two carbon atoms (H3-B). The magnitude of the Al-2 adsorption energy is larger than that of an adsorbed Al atom. While the ground states for both free Al-2 and isolated defective graphene is predicted to be a triplet, that corresponding to the dimer adsorbed on the monovacancy is calculated to be a singlet. Charge population analysis has shown that a significant electron transfer from Al to the substrate of about 2e is produced. The corresponding density of states (DOS) obtained with periodic conditions indicate that the Al-2/defective graphene system at the H3-B geometry with a doping level of about 3% has a nearly zero band gap with almost no states at the Fermi level, unlike the situation where only one Al atom is adsorbed on the monovacancy which present a metal-like behavior. (C) 2015 Elsevier B.V. All rights reserved.