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 in the channeling trajectory: one including only valence electrons (Li[2s¹]) and another including core electrons (Li[1s²2s¹]). 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. 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. In addition, chemical-bond formation and charge capture serve as additional 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 S_e in lithium and provides a theoretical basis for assessing irradiation damage in lithium materials used in fusion devices.