Combining two types of molecular dynamics for rapid computation of high-energy displacement cascades. II. Application of the method to a 70-keV cascade in a simplified nuclear glass

Abstract

A combined molecular dynamics method is proposed to accelerate the computation of displacement cascades in nuclear glass arising from recoil nuclei in the 70\char21{}100 keV energy range. The method combines two types of molecular dynamics calculations: classical MD with standard empirical potentials and a simplified form with the potentials reduced to their short-range component to estimate the morphology of a displacement cascade. With this method we were able to reconstitute the behavior of a simplified oxide glass impacted by a 70-keV projectile. Compared with the results obtained by classical molecular dynamics, mechanisms observed at lower energies (temporary depolymerization followed by progressive structure recovery) are correctly reproduced at 70 keV; the number of atom displacements and the intermediate depolymerization peak intensity remain linear at energies ranging from 0 to 70 keV. The large volume of the 70-keV cascade allowed us to demonstrate that structure recovery was not homogeneous: the coolest regions were less annealed than the hottest regions. The residual depolymerization was more intense in regions struck by lower-energy projectiles\char22{}i.e., at the end of the cascade. Local thermal agitation in the hottest regions rapidly diminished as it propagated, and the neighboring regions were largely unaffected. Thermal agitation in the hottest regions thus had little effect on the recovery of regions impacted by low-energy projectiles.