Characterization of energy conservation in primary knock-on atom cascades: Ballistic phase effects on variable time steps

Non-equilibrium molecular dynamics simulation trajectories must in principle conserve energy along the entire path. Processes exist in high-energy primary knock-on atom cascades that can affect the energy conservation, specifically during the ballistic phase where collisions bring atoms into very close proximities during which time important physics may be overlooked. The solution, in general, is to reduce the time step size of the simulation. This work explores the effects of variable time step algorithms and the effects of specifying bounds. The temporal and spatial extents of the ballistic phase can be well characterized by applying coarse-graining methods developed to monitor the kinetic energy dissipation during a high-energy cascade.