First-principles investigation of radiation induced defects in Si and SiC

We have calculated the displacement-threshold energies for the main symmetry directions in Si and SiC using a self-consistent first-principles method. We show that – depending on the knock-on direction – 64-atom simulation cells can be sufficient to allow a nearly finite-size-effect-free calculation, thus making the use of first-principles methods possible. We use molecular dynamics (MD) techniques and propose the use of a sudden approximation which agrees reasonably well with the MD results for selected directions and which allows estimates of displacement-threshold energies without employing an MD simulation.