Electronic structure of polymeric KC60 - a crystal orbital analysis

The band structure of orthorhombic KC60 is investigated by a crystal approach based on an intermediate neglect of differential orbital Hamiltonian. The title compound crystallizes in the space group Pnnm with covalent intermolecular carboncarbon bonds. Polymeric KC60 is a metal with a low electronic density of states (DOS) at the Fermi energy ϵF. This metallic behaviour differs from the electronic ground state calculated for isotropic fcc KC60 with potassium occupying the octahedral intersitial site. The reduced width of the conduction band in the fcc structure favours an insulating Mott state relative to the metallic configuration. The dimensionality of the title compound is discussed on the basis of intercell energies, the DOS profile and dispersion curves. The theoretical results are compared with experimental observations. Wiberg bond-indices are employed to describe the chemical bonding within the distorted C60 soccerball.