DFT and direct MD study of the diffusion of sodium ion on graphenes

The structures and electronic states of sodium ion (Na + ) trapped on the graphene have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of interaction between Na + and the graphenes. In addition, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa, J. Phys. Chem. C, 112 (2008) 10193] was applied to diffusion processes of the Na + ion on graphene. The graphene composed of 37 benzene rings was used as a model of graphene. The B3LYP/LANL2MB calculation showed that the sodium ion is stabilized in hexagonal site and is located at ca. 2.230 A from the graphene surfaces. The direct MO-MD calculation showed that the Na + ion diffuses freely on the graphene surface, but the ion did not approach the edge region due to the fact that a high potential barrier exists near the edge region. The nature of interaction between Na + and graphene was discussed on the basis of theoretical results.