Electronic Structure of Polymerized C60 Phases

The band structure and solid state electronic properties of three polymerized C₆₀ phases are investigated by a crystal orbital (CO) approach based on an intermediate neglect of differential overlap (INDO) Hamiltonian. We have considered a one-dimensional (1D) body-centered orthorhombic phase as well as two 2D phases crystallizing in a body-centered tetragonal and a rhombohedral lattice. The CO results derived for the polymerized C₆₀ systems are correlated with electronic structure data of the isotropic body-centered cubic van der Waals crystal. We analyze the energy bands ϵ_i(k), the associated electronic density of states (DOS) profiles as well as the atomic net charges and so-called Wiberg bond indices which measure the strength of covalent bonds. The formation of intermolecular CC σ bonds leads to an enhanced alternation between formal double and single bonds on the soccerball. The dimensionality of the four C₆₀ fullendes considered is discussed on the basis of the different quantities evaluated by the CO formalism. The theoretical results are supplemented by C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of polymerized and non-polymerized C₆₀ films before and after oxygen contamination.