Quantum electron dynamics in helium ion injection onto tungsten surfaces based on time-dependent density functional theory

Abstract

The neutralization of an ion particle on a surface is a key issue in plasma–wall interactions. We investigated helium ion injection onto a tungsten surface using time-dependent density functional theory (TDDFT) simulations. We developed the TDDFT code QUMASUN and simulated the process of electron transfer from the surface to the He nucleus by simultaneously solving the time evolution of the electron wavefunction and the classical motion of nuclei. Our results show that the probabilities of ${\text{He}}^{2+}$ changing into ${\text{He}}^{1+}$ and ${\text{He}}^0$ on the surface are approximately 40% and 25%, respectively. The electrons captured by ${\text{He}}^{1+}$ and ${\text{He}}^0$ predominantly occupy the 2s and 2p orbitals, respectively, corresponding to the excited states. In addition, this paper reports the challenges encountered while applying TDDFT to PWI research.