Diffusion of Li+ ion in graphite cluster model at 800 K: a direct molecular orbital dynamics study Original Research Article

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 are considered, suggesting that the Li+ ion is rather stable at the two distinct sites in the bulk where the potential energy difference between them is 2.0 kcal/mol. For the Li+ ions stabilized at these two sites, the diffusion processes were simulated at 800 K through the direct molecular orbital dynamics procedure which was newly developed by one of the present authors. No jumping diffusion occurs with Li+ ions among the stabilization sites, but they diffuse along the outline of the cluster model with the fluctuations. It takes 2.0 ps for a Li+ ion to diffuse from the lower potential site to another equivalent site. On the other hand, it takes 0.7 ps to move from the higher potential site to the unstable circumference site composed of corner (armchair edge) carbon atoms. As the result, the diffusivity is approximated as 10−8–10−7 m2/s.