  The accurate treatment of electronic effects in multi-million atom
simulations of radiation-induced collision cascades is crucial for reliable
predictions of primary radiation damage. In this work, we explore the
performance of a recently developed two-temperature molecular dynamics model
implementing an electron density-dependent coupling of electronic and atomic
subsystems for cascade simulations in nickel. We show that the parameter-free
model realistically captures the instantaneous energy losses during all stages
of the highly non-equilibrium cascade process. Simulations predict two distinct
coupling regimes, corresponding to the rapid electronic stopping energy losses
in the early stages of the cascade and to the electron-phonon coupling
mechanism in the later stages, without the use of separate coupling terms. The
intermediate stage of the cascade dynamics displays a complex energy transfer
between the subsystems, which cannot be validated by comparison to either
electronic stopping or electron-phonon coupling theories. We therefore compare
the predicted atomic mixing, which is sensitive to the energy losses during the
intermediate cascade stage, with experimental ion beam mixing measurements. We
find good agreement with the experiments, validating the coupling model for the
intermediate stage of cascades. Predictions of final defect numbers and cluster
sizes are found in line with the predictions of conventional electronic
stopping-based methods, while significantly reducing the theoretical
uncertainty in the predictions of conventional models stemming from arbitrary
choices of thresholds for different coupling terms. Our results represent a
notable improvement in cascade damage predictions in nickel, providing
validation of the electron density-dependent coupling model for radiation
damage simulations in general.
