Electronic stopping power of magnesium including inner-electron excitation

The electronic stopping power of magnesium for protons and He ions is studied by a nonequilibrium approach based on real-time time-dependent density-functional theory combined with Ehrenfest molecular-dynamics simulation. The electronic stopping power of Mg for energetic protons and He ions is calculated, and the microscopic excitation mechanism for the inner 2p electron of Mg and its contribution to electronic stopping power is revealed. In the low-energy range, the velocity proportionality of the electronic stopping power of Mg for protons is displayed. The low-energy stopping power of Mg for He ions displays deviations from the velocity proportionality, which is ascribed to the electronic structure of He ions that enables an additional energy-loss channel due to charge exchange. Our calculated stopping power is in a quantitative agreement with the experimental data up to the stopping maximum, and the stopping power including also 2p-electron excitation is considerably improved compared to that with only the valence electron taken into account. Our results showed that the contribution of p-electron excitation to the electronic stopping is remarkable in the high-velocity regime. The scaling relationship Sα/SH = q¯α/q¯H can be extended to low velocities provided that the mean steady-state charge is employed instead of assuming fully ionized charges and considering also 2p-electron excitation of Mg.