Global minima of (C60)nCa2+, (C60)nF− and (C60)nI− clusters

Likely candidates for the lowest potential energy minima of (C60)nCa2+, (C60)nF− and (C60)nI− clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C60 intermolecular interaction, an averaged Lennard-Jones C60-ion interaction, and a polarisation potential, which depends on the first few non-vanishing C60 multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C60)n cluster, the coordination shell being tetrahedral for Ca2+ and F−. The I− ion has an octahedral coordination shell in the global minimum for (C60)6I−, however for 12 ⩾ n ⩾ 8 the preferred coordination geometry is trigonal prismatic.