Electronic stopping of iron for protons and helium ions from first-principles calculations

The electronic stopping power and charge state of protons and helium ions irradiating iron under both channeling and off-channeling geometries are studied by first-principles molecular dynamics. Using real-time time-dependent density functional theory, the inner-electron excitation of iron under ion irradiation is explored. The calculated electronic stopping powers, which take into account the effects of inner-electron excitation, were found to be in good agreement with experimental data. To further investigate the charges attracted by the projectiles moving in iron, we introduced a modified method to decompose the charges into the occupations of the respective projectile orbitals. When the projectile ion moves along off-channeling trajectories, the orbital distribution of the charges attracted by protons is found to be unstable, while that of helium ions remains relatively stable. However, it is worth noting that the orbital distribution differs between the channeling and off-channeling cases for both protons and helium ions. Overall, our research provides insight into the electron capture behavior of protons and helium ions as they traverse through iron.