The electronic structure of KC8

Abstract

Abstract The preliminary results of an ab initio band structure calculation for first stage potassium graphite, KC8, are presented. We use the presently accepted crystal structure with 18 atoms per unit cell (space group Fddd). The crystal potential is constructed with overlapping atomic charge densities for K+1 and C -1 8 , using Xα exchange approximation. Band structure results show general correspondence with the bands of two dimensional graphite “folded” into the Brillouin zone of KC8. The 3p core states of potassium are found to lie a few eV above the bottom of the C σ bands. The 4s valence bands of potassium are found to have minima near the Fermi level of KC8, distorting the graphite π bands in the vicinity of the Fermi level. The effects of this distortion on the Fermi surface of KC8 are discussed. In addition, the K 4s levels hybridize with several of the low lying π and σ bands of graphite, indicating an element of covalency in the potassium-carbon interaction.