Multiscale modeling of electron-ion dynamics in silicon under particle radiation

Effects of fast ions impacting solids are important, in order to quantitatively understand radiation damage, ion beam modification (e.g.\ helium microscopy), or ion implantation. The interaction of a fast ion with kinetic energies in the MeV range and a target involves both electron-ion as well as ion-ion collisions. Ehrenfest molecular dynamics, based on real-time propagation of time-dependent Kohn-Sham equations, provides highly accurate insight into early stages of the defect-formation process and, in particular, into electronic stopping. Thanks to the excellent scalability of our plane-wave implementation, we are capable to perform these parameter-free simulations for supercells with hundreds of atoms using high-performance computing. However, the cost of Ehrenfest dynamics is prohibitively high for entire radiation-cascade development both regarding length- and time scales. Results from TDDFT for silicon targets are used to provide much more accurate information on velocity- and position-dependence of electronic stopping that we transfer into classical molecular dynamics. This results in a multi-scale simulation framework capable of studying crystalline semiconductors such as Si, GaP, or InP.