Charge equilibration and electronic stopping for silicon projectiles in silicon

Understanding the effect of highly energetic particle radiation on semiconductors from first principles is important, e.g. for radiation hardness as well as ion implantation to create quantum bits. Previously we successfully used Ehrenfest molecular dynamics and real-time time-dependent density functional theory to describe electronic stopping during the early stages of radiation damage for light projectiles. Our recent results for heavier (silicon) projectiles traversing silicon bulk crystals show a pronounced dependence of electronic stopping on the initial condition, which we relate to the charge of the projectile. Not only was this effect absent for light projectiles, but on a femtosecond time scale this also depends on whether the target material is a metal or semiconductor. We analyze these recent results in terms of charge equilibration and contributions of core and valence electrons to electronic stopping. Developing a consistent picture from first principles is necessary to describe electronic friction in classical molecular dynamics with predictive accuracy.