Tight binding studies of exohedral silicon doped C60

We study the exohedral doping of C60 fullerenes by silicon atoms. The structural properties and stability of C60Sim aggregates, with m in the range 1–15, are investigated using a non-orthogonal tight binding model. For each cluster size an extensive set of possible configurations has been considered in order to increase the likelihood of determining the lowest energy structure. Each configuration was then minimised using the conjugate gradients algorithm. We find that for cluster sizes up to C60Si5 the trend is for Si atoms to aggregate, forming a monolayer on the C60 surface, while for C60Sim with m equal to 5 and beyond the trend changes towards the formation of three dimensional Si clusters attached to the fullerene surface. For m>8 the additional Si atoms place themselves on the Si already present, and not directly on the buckyball surface. We have also conducted dynamical simulations of cluster fragmentation, which indicate that when the fragmentation of C60Sim takes place, it generates two homonuclear pieces, i.e., a Sim cluster and the C60 fullerene, which remains intact, in agreement with photofragmentation experiments.