Tight-binding molecular dynamics simulations of radiation-induced fragmentation of C60

The fragmentation of the C-60 fullerene was investigated using tight-binding molecular dynamics simulations based on the parametrization of Papaconstantopoulos [MRS Symposia Proceedings No. 491 (Materials Research Society, Pittsburgh, 1998), p. 221]. Averaged fragment size distributions over random sets of initial configurations were obtained from simulations of radiation-induced fragmentation in the 50-500 eV excitation energy range. The excitation caused by the radiation was simulated simply by ascribing suddenly random velocities to each atom of the fullerene cage. For low excitation energies, the size distributions are peaked for dimers (reflecting a preferential C-2 emission) and a bimodal size dependence characterizes the distributions of the complementary small and large fragments. For high excitation energies, predominantly multifragmentation occurs, but a genuine power-law dependence of small fragments is not yet observable. A phase transition is found for rather low excitation energies (100-120 eV).