Quantifying the impact of an electronic drag force on defect production from high-energy displacement cascades in α-zirconium

Abstract

Molecular dynamics displacement cascade simulations with PKA energies up to 40 keV at 600 K have been performed to investigate the impact of electronic energy losses in α-zirconium. The following data sets are compared: 1) displacement cascades performed with nuclear stopping only and 2) displacement cascades with simultaneous nuclear and electronic stopping. Electronic energy losses are modeled by a drag force with strength proportional to the energy-dependent electronic stopping power using the intrinsic “fix electron/stopping” command in LAMMPS. Consistent with typical characteristics of cascade defect generation, the production efficiency of Frenkel pairs falls below 20% of the NRT-predicted value for high PKA energies, defect clustering increases with PKA energy, and two distinct power-law regimes of the form NF=A(Ep)mcorrelate the surviving number of Frenkel pairs; the separate power-law fits describe defect production prior to and following sub-cascade formation. When implemented, electronic energy losses account for a 10–20% reduction in surviving Frenkel pairs for high-energy PKAs. The energy loss method implemented in LAMMPS results in nuclear damage energies comparable with the values predicted by SRIM using the full-cascade option, and represents a user-friendly method to incorporate ionization losses in molecular dynamics simulations.