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 εi(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