The lithium (Li)-graphite intercalation compounds are put to practical use as a negative electrode of the Li-ion battery. In this material, it is important to understand not only the static electronic structure but also the dynamics of Li simultaneously. We apply originally developed hybrid quantum (QM)-classical (CL) simulation code to analyze diffusion processes of the Li-graphite intercalation compound. The region including the inserted Li and neighboring C atoms is treated with electronic state by the real space density-functional theory (DFT), and this region is embedded in a CL system of the C atoms of graphite based on an empirical interaction model. For inter-layer interaction of graphite, an atomic potential model based on Lennard-Jones potential is originally constructed and added in a CL molecular dynamics calculation of the whole system. Buffered cluster method is adopted to couple the QM and CL boundary. The valence electron density of Li obtained by DFT calculation is almost zero and the Li in graphite layers is considered as Li cation (Li~+). The QM region is adjusted to the movement of Li. The diffusion coefficient calculated by the mean-square-displacement of Li atom in the present hybrid dynamics is in good agreement with experimental one.
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