Radiation Damage Cascades in Fullerite Using Molecular Dynamics

Molecular dynamics is used to study radiation cascades in solid C60 under ambient conditions. Simulations are performed for Primary Knock-On Atom (PKA) energies from 0.1 to 1 keV, and cascades are sampled over many PKA directions to collect statistics. Energies and forces are described using the Environment Dependent Interaction Potential for carbon paired with the Ziegler-Biersack-Littmark potential for short-range interactions, and cascade behaviour is characterized by tracking kinetic energy, hybridization and bond connectivity as a function of time. Compared to most materials, fullerite exhibits an unusual radiation response due to weak thermal transfer between C60 molecules leading to a thermalization phase lasting hundreds of picoseconds. The cascades damage the C60 molecules and link them together, and a linear relation is found between the number of cross-linked molecules and the number of new sp3 atoms. The threshold displacement energy computed is 18 eV, in agreement with experiments