Dirac-Fock-Slater calculations on the geometric and electronic structure of neutral and multiply charged C-60 fullerenes

Using a self-consistent relativistic molecular Dirac-Fock-Slater method we have determined the geometric structures and ionization energies of C-60(X+) (x = 0-7). The lengths of the bonds for the pentagonal edge (single bonds) and the bonds shared by hexagonal rings (double bonds) are found to increase as a function of charge state with an expansion of the cage. The binding energy per atom of C-60(x+) (x = 0-7) shows a quadratic dependence on the charge state of the C-60 cluster and an extrapolation to higher charge states reveals that C-60(x+) Should still be bound up to x = 13. Charging of the clusters are analysed using a classical capacitance model and compared with results from other calculations. Calculated ionization potentials are found to increase linearly with the charge while the available experimental data with comparatively big uncertainties indicate a small quadratic dependence.