Structures and energetics of lithium adatom and its dimer on graphene-a DFT study

We performed a systematic density functional theory (DFT) study of the adsorption of Lithium adatom and its dimer on graphene using SIESTA package [1], in the generalized gradient approximation (GGA). The adsorption energy, geometry, charge transfer and density of states of adatom/dimer-graphene system are calculated. The calculations showed that the interaction between Li adatom and graphene is strong(similar to 1.07 eV) and it prefers to adsorb on H-site. Further calculations of both horizontally and vertically aligned dimers show that the adsorption is also weak for the latter orientation. The preferred orientation of each dimer was found to be parallel to graphene sheet with the two atoms of the dimer occupying adjacent H-sites on the graphene. Significant charge transfer (similar to 0.388e) from Li adatom to graphene will induce electric dipole moments in the adatom/graphene system. We also calculated DOS for the stable Li - graphene system. The Fermi energy is seen to lie above the Dirac point inside the conduction band indicating that appreciable electrons are transferred from the Li adatom to the graphene sheet. We also noticed that the adsorption of Li adatom/dimer on graphene causes very little distortion to the graphene lattice. (C) 2014 Elsevier B.V. All rights reserved.