Electronic States of Fullerenes on Silicon Surfaces

Electronic states of a model cluster C70Si70H46 of the C70 molecule on the Si(111)7×7 surface are calculated by the discrete variational Xα ( DV- Xα) method with the linear combination of atomic orbital (LCAO) basis. Due to the electron transfer from the Si substrate, the molecule has an ionicity, C70 -2.31. The highest occupied molecular orbital (HOMO) is the dangling bond orbital of the Si surface. Six occupied orbitals and five unoccupied orbitals near the HOMO of the C70 molecule have high charge density around single bonds on pentagons. The maximum point of these charge densities over one half of the C70 molecule is about 0.5 Å higher than that over the other half of the C70 molecule. The charge density of three occupied (two unoccupied) nearly degenerate orbitals is high in three (four) regions over the C70 molecule which has nearly C s ( D2) symmetry. This should be compared with the STM images of the adsorbed C70 molecule.