Real-time proton-induced electron and ion dynamics in MgO slab

Ion beam irradiation has been extensively employed to precisely tailor the electronic and optical properties of thin film materials with nanometric precision. The success of these experiments underscores the need for a comprehensive understanding of the interaction between the ion projectile and the electronic and ionic systems of host materials, which is under development. In this project, we use real-time time-dependent density functional theory, which provides a unified framework for ion-induced electron excitation and the initial stages of nuclear damage, to investigate the response of MgO to proton irradiation. Our results reveal that, the excited electrons, localized near proton impact point, do not promptly reach equilibrium due to the relatively low electron mobility in an insulator. Consequently, this non-equilibrium state leads to an enhancement of the Coulomb repulsion, resulting in a constant force of approximately 1-2 eV/Å on atoms closest to the proton impact point, after the proton exits the MgO slab. Furthermore, these forces rapidly diminish as the distance from the proton impact point increases, indicating the potential utility of light ion irradiation for inducing localized defects with nanoscale precision. Moreover, this proof of concept drives our ongoing investigations into other materials systems with greater experimental interest.