Solid state electronic structure of potassium graphite intercalation compounds; The systems KC24 and KC8

The solid state electronic structures of the potassium graphite intercalation compounds (GIG) KC24 and KC8 are investigated by a crystal orbital (GO) approach of the intermediate neglect of differential overlap (INDO) type. KC24 crystallizes in a hexagonal and KC8 in an orthorhombic lattice. The CO results derived for the potassium GIC are compared with CO results of pristine graphite and potassium-doped C-60 fullerides. An incomplete It-to-graphite charge transfer (CT) of about 50% is predicted for both GIC studied. This incomplete CT in GIC is correlated with the incomplete CT in potassium-doped fullerides predicted in a recent study. The present results call be considered as all a posteriori corroboration of our findings in the case of alkali-doped fullerides. The acceptor capability of graphite is smaller than the one of the C-60 soccerball with its pentagon defects. Modifications in the electronic density of states (DOS) distribution in the potassium GIC relative to pristine graphite are analyzed. The influence of the excess electrons oil the graphite electronic structure is described by a parameter which measures the ''number of covalent bonds'' per CC contact.