▎ 摘　　要

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.