I am running consecutive PKA cascades on the same simulation box with periodic boundaries on all sides to accumulate damage. The choice of PKA atom is randomized and uniform irradiation is also ensured. There are thermostats on thin boundary layers on all sides maintained at 300 K. PKA energy is like 1 keV and box size is like 20x20x20. Time step is 1 fs with adaptive modification. A Restart file is written after every cascade is run, which is read for the next cascade to begin. Each cascade is sufficiently allowed to evolve so that any additional energy in the system is minimum. Everything is running fine, but when the point defects are analyzed (using the OVITO - Wigner-Seitz method) there are oscillations in the numbers of point defects, i.e., increasing slowly in a linear graph then suddenly becomes very high number (10 to 100 times a value) reaches a maximum value and then decreases to a very low value - this pattern is continuing with the increasing number of cascades. The overall number of vacancies / interstitials as a result do not increase. I do not find any explanation for this.
Please help me.
Thank you for your time.