The electronic structures of the stage-1 hydrogen-potassium-graphite ternary intercalation compounds ${\mathrm{C}}_4$${\mathrm{KH}}_{\mathit{x}}$ are investigated. The band structures of these compounds are determined in a Hohenberg-Kohn-Sham local-density-functional formalism using the self-consistent numerical-basis-set linear combination of atomic-orbitals method. Our band-structure calculation is carried out for ${\mathrm{C}}_4$ ${\mathrm{KH}}_{\mathit{x}}$ with three assumed in-plane superlattice models of hydrogen structure: (a) (2×2)R(0°) model (x=0.5); (b) (2× √3 )R(0°,30°) model (x=0.5); (c) (1× √3 )R(0°,30°) model (x=1.0). In these three cases, we estimate the amount of the charge transfer among the individual atoms and show that the hydrogen atom acts as an acceptor to graphite, while the potassium atom acts as a donor. The charge transfer to the hydrogen atoms is imperfect and therefore the hydrogen 1s state forms a partially occupied metallic band. This hydrogen 1s-like band coexists with the graphite ${\mathrm{\pi }}^{\mathrm{*}}$-like bands at the Fermi level. These results indicate that ${\mathrm{C}}_4$${\mathrm{KH}}_{\mathit{x}}$ has features like those of two-dimensional metallic hyrodgen.

• Received 2 October 1989

DOI:https://doi.org/10.1103/PhysRevB.41.4938