Using the hydrogen terminated planar cluster model, C54H18, the stabilization site of Li+ ion was determined by the unrestricted Hartree-Fock (UHF) AM1 energy gradient method. Six kinds of stabilization sites were considered, suggesting that the Li+ ion was rather stable at the two distinct sites in the bulk where the potential energy difference between them was 2.0kcal/mol. For the Li+ ions stabilized at these two sites, the diffusion processes were simulated at 800K through the direct molecular orbital dynamics procedure which was newly developed by one of the present authors. No jumping diffusion occurred with Li+ ions among the stabilization sites, but they diffuse along the outline of the cluster model with the fluctuations. It takes 2.0ps for a Li+ ion to diffuse from the lower potential site to another equivalent site. On the other hand, it takes 0.7ps to move from the higher potential site to the unstable circumference site composed of corner (armchair edge) carbon atoms. As the result, the diffusivity was estimated to be 10-8 to 10-7m2/s.

Diffusion of Li+ Ion in Graphite Cluster Model at 800K: a Direct Molecular Orbital Dynamics Study. Shimizu, A., Tachikawa, H.: Journal of Physics and Chemistry of Solids, 2002, 63[4], 619-24