Charge density and charge transfer in stage-1 alkali-graphite intercalation compounds

First-principles electronic structure calculations are carried out for the stage-1 alkali graphite intercalation compounds LiC6 and XC(8) (X = Li, Na, K, Rb, and Cs). We analyze the charge densities and the differences to the reference charge densities of graphite host and intercalant sublattice. For the alkali metals Na, K, Rb, and Cs the computed charge transfer is nearly constant at a value of 0.7 elementary charges (e); values of 0.5e and 0.4e are found for the Li compounds LiC6 and LiC8, respectively. It is shown that the main fraction, about 0.4e, of the charge transfer is a geometrical consequence of the simple overlap of the charge densities of the graphite and intercalant sublattices.