Excitation effect of d electrons on the electronic energy loss of energetic protons colliding with a Zn atom

Abstract

By using a nonequilibrium approach based on real-time time-dependent density-functional theory combined with molecular dynamics simulations, the effects of $d$-electron excitation on the electronic energy loss of energetic protons colliding with atomic zinc target are studied. The results show that the semicore electrons play a crucial role in the electronic energy loss in an extended energy range. In the low-energy regime, the electronic energy loss displays the threshold effect before it is proportional to velocity, which is explained by the quantization of the energy levels of zinc atom, and the charge transfer contributes greatly to the electronic energy loss, especially at 0.1 a.u. In addition, due to the electron resonance excitation, the number of excited electrons and charge transfer is significantly increased at the velocity thresholds for electron excitation. In the high-energy regime, the electronic energy loss is greatly enhanced as the the impact parameter decreases, which is ascribed to the excitation of $3d$ electrons. We also calculated the stopping cross section for energetic protons colliding with atomic zinc, which is in a good agreement with the experimental values in both low- and high-velocity regimes.