We report on molecular Dynamics (MD) simulations carried out in fcc (Cu) and bcc metals (W) using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code to study (i) the statistical variations in the number of Frenkel Pairs produced by energetic primary knock-on atoms (PKA) (0.1-5 keV) directed in random directions and (ii) the in-cascade cluster size distributions. It is seen that more than 100 random directions have to be explored for the variance in the number of Frenkel pairs produced to become steady in the case of fcc Cu, whereas for bcc W at least 60 random directions need to be explored. It is also seen that most of the interstitials are single in all cases. The number of Frenkel pairs produced in the MD simulations are compared with that from the Binary Collision Approximation Monte Carlo (BCA-MC) code SDTRIM-SP and the results from the NRT model. It is seen that a proper choice of the damage energy, i.e. the energy required to create a stable interstitial is essential for the BCA-MC results to match the MD results. On the computational front it is seen that in-situ processing saves the need to input / output (I/O) atomic position data of several tera-bytes when exploring 1000 random directions and there is no difference in run-time because the extra 1 run-time in processing data is offset by the time saved in I/O.
The micro-structural properties of materials change due to irradiation. The defects formed during the displacement cascades caused by irradiation are the primary source of radiation damage (Björkas, Nordlund, & Caturla, 2012; Stoller, 2012). The number of primary defects produced, defect cluster size distribution, and defect cluster structures after a collision cascade can be studied using Molecular Dynamics simulations. These results determine the long term evolution of the micro-structural changes in the material (
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