Effects of core electrons on electronic stopping power in proton-irradiated lithium nanosheets

As the solid metal with the lowest atomic number, lithium is a typical material for investigating electronic stopping power. We investigate the electronic stopping power of lithium nanosheets for protons using real-time time-dependent density functional theory combined with Ehrenfest molecular dynamics simulations. To elucidate the role of core electrons in the energy dissipation process, we systematically compare two pseudopotential models for Li: one including only valence electrons (Li[2s1 ]) and another including core electrons (Li[1s2 2s1 ]), for both channeling and off-channeling trajectories. The results indicate that in the low-velocity regime (v ≤ 0.2 a.u.), the energy transferred by the proton is insufficient to excite the 1s core electrons; the S e is entirely dominated by valence electrons, and is insensitive to the incident trajectory. When the velocity exceeds the threshold, the contribution of core electrons gradually emerges: in the intermediate velocity regime, dynamic polarization of the electron cloud serves as the main channel to indirectly boost valence-electron excitation; at high velocity (v = 1.0 a.u.), direct ionization of 1s electrons occurs, serving as a dominant energy dissipation channel. In addition, chemical-bond formation and charge capture serve as supplementary dissipation mechanisms, with the electron-capture effect being most pronounced at a proton velocity of 0.6 a.u. This study elucidates the contribution of core electrons to the Se in lithium and provides a theoretical basis for assessing irradiation damage in lithium materials used in fusion devices.