Computer aided-molecular design of high performance nano-carbon materials: Na+ on graphenes

The electronic states of sodium ion (Na+) trapped on the model surfaces of amorphous carbon have been investigated by means of hybrid density functional theory (DFT) calculations to elucidate the nature of interaction between Na+/Na and the amorphous carbon surfaces. Also, direct molecular orbital–molecular dynamics (MO–MD) calculation [Tachikawa and Shimizu, J. Phys. Chem. B, 110 (2006) 20445] was applied to diffusion processes of the Na+ ion on the model surface of amorphous carbon. Seven models of graphene sheets (n = 7, 14, 19, 29, 37, 44 and 52, where n means numbers of rings in each carbon cluster) were considered in the present study. The B3LYP/LANL2MB calculations showed that the sodium ion is located at 2.24–2.26 Å from the graphene surfaces. The direct MO–MD calculations showed that the Na+ ion diffuses freely on the surface above 300 K. At higher temperature (1100 K), the Na+ ion moved from the center to edge region of the model surface. The nature of the interaction between Na+ and the amorphous carbon surfaces was discussed on the basis of theoretical results.