Structural Energies in Stage-One Graphite Intercalation Compounds

A Thomas-Fermi density-functional theory is developed for structural energies in stage-one alkali-graphite intercalation compounds. Correct trends for lattice constants and elastic moduli are obtained. We compute corrugation energies $\Delta E$ and alkali-alkali spring constants $k$, which determine in-plane intercalant diffusion and domain-wall structure. $k$ is determined by electrostatic effects, and is mainly independent of intercalant. $\Delta E$ depends strongly on intercalant size; thus Li differs substantially from K, Rb, and Cs.