Lithium-intercalated graphite: Self-consistent electronic structure for stages one, two, and three

First-principles electronic structure calculations were carried out for Li${\mathrm{C}}_6$, Li${\mathrm{C}}_{12}$, and Li${\mathrm{C}}_{18}$ representing first-, second-, and third-stage model graphite intercalation compounds. By comparing the charge density of these compounds to that of reference graphite compounds, we could define a "total difference density" in order to quantify charge transfer and polarization in these materials. The total difference density is found to be highly concentrated near the intercalant ions. However, the conduction electrons (those in partially occupied bands) are found to have the distribution of virtually undistorted $\pi$ wave functions and have a much more delocalized distribution than that of the total difference density. These two types of charge distributions account for many of the unusual electronic properties of graphite intercalation compounds.