  We locate putative global minima for (C_60)_N clusters modelled by the
potential of Pacheco and Prates-Ramalho up to N=105. These minima are based on
icosahedral packing up to N=15, but above this size the lowest-energy
structures are decahedral or close-packed. Although structures based on the
98-molecule Leary tetrahedron, which have been inferred from experiment, are
not lowest in energy for this potential, an examination of the energetics of a
growth sequence leading to the Leary tetrahedron lends further support to the
experimental assignments. An analysis of the potential energy surface
topography and the thermodynamics of two example clusters indicates that the
multiple-funnel topography is likely to have a strong influence on the dynamics
of structure formation and that solid-solid transitions driven by differences
in vibrational entropy are likely to be common.
