The structures and electronic states of sodium ion (Na+) trapped on graphene were investigated by means of density functional theory calculation to elucidate the nature of interaction between Na+ and the graphenes. In addition, direct molecular orbital-molecular dynamics calculation (Tachikawa, 2008) 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 calculation showed that the sodium ion was stabilized in hexagonal site and was located at about 2.230Å from the graphene surfaces. The direct molecular orbital-molecular dynamics 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 existed near the edge region. The nature of interaction between Na+ and graphene was discussed on the basis of theoretical results.

DFT and Direct MD Study of the Diffusion of Sodium Ion on Graphenes. Tachikawa, H., Kawabata, H.: Thin Solid Films, 2009, 518[2], 873-6