Direct molecular orbital-molecular dynamics calculations were applied to the diffusion of a Li atom on a model surface of amorphous carbon (figure 2) and a comparison was made with the diffusion mechanism of Li+ ions. A carbon sheet composed of C96H24 was used as the model surface. The total energy and energy gradient on the full dimensional potential energy surface of the LiC96H24 system were calculated at each time step in the trajectory calculation. The optimized structure, where the Li atom was located at the center of mass of the model surface, was used as the initial structure at zero time. Simulation temperatures were chosen in the range of 200 to 1250K. The dynamics calculations showed that the Li atom vibrated around the initial position below 250K, and it moved above 300K. At moderate temperatures, the Li atom translated freely on the surface. At higher temperatures (1000K), the Li atom moved from the center to the edge region of the model surface and was trapped in the edge. The activation energy calculated for the Li atom was larger than that for the Li+ ion. This difference was due to the fact that the Li atom diffused together with an unpaired electron on the carbon surface.

Diffusion Dynamics of the Li Atom on Amorphous Carbon: a Direct Molecular Orbital-Molecular Dynamics Study. Tachikawa, H., Shimizu, A.: Journal of Physical Chemistry B, 2006, 110[41], 20445-50