Adsorption of Two Sodium Atoms on Graphene - a First Principles Study

We perform a systematic density functional theory (DFT) study of the adsorption of two sodium atoms on graphene using the SIESTA package, in the generalized gradient approximation (GGA). The adsorption energy, geometry, magnetic moment and charge transfer of the Nan-graphene (n=1, 2) system are calculated. Three initial horizontal orientations of the pair of sodium atoms on graphene are studied. Our calculations reveal that sodium atoms bind weakly to the graphene surface which is in agreement with previous results. We also notice a charge transfer of 0.288e from a sodium adatom to the graphene sheet altering its magnetic moment (-0.318 mu(B)) that is reduced from the gas phase value of the isolated atom (1 mu(B)). The calculated adsorption energies suggest that clustering of Na atoms on graphene is energetically favorable.