The electronic states of potassium ion and atom (K+ and K) adsorbed on the amorphous carbon surfaces were investigated by means of hybrid density functional theory calculations to elucidate the nature of interaction between K+/K and the amorphous carbon. Seven graphene sheets (n = 7, 14, 19, 29, 37, 44 and 52, where n means numbers of rings in each carbon cluster) were considered as models of amorphous carbon in the present study. The calculations showed that the potassium ion was located at about 2.80Å from the graphene surfaces and the charge of K+ was not dependent upon the cluster size of the graphene sheets. On the other hand, the charge of potassium atoms increased with increasing cluster size (n), and it reached a constant value (ca. +0.70) at n = 29 to 52. Also, direct molecular orbital-molecular dynamics calculation (Tachikawa and Shimizu, 2006) was applied to diffusion processes of the K+ ion and K atom on the model surfaces of amorphous carbon. The direct molecular orbital-molecular dynamics calculations showed that the K+ ion and K atom diffused freely on the surface at 800K. The nature of the interaction between K+/K and the carbon clusters was considered on the basis of theoretical results.

Direct ab initio Molecular Dynamics Study on the Diffusion of Alkali Ions on Amorphous Carbon. Iyama, T., Kawabata, H., Tachikawa, H.: Japanese Journal of Applied Physics, 2008, 47[1,2], 803-5