Parameter-free modelling of dislocation motion: the case of silicon

In silicon and other materials with a high Peierls potential, dislocation m otion takes place by nucleation and propagation of kink pairs. The rates of these unit processes are complex unknown functions of interatomic interact ions in the dislocation core, stress and temperature. This work is an attem pt to develop a quantitative physical description of dislocation motion in silicon based on understanding of the core structure and the energetics of core mechanisms of mobility. Atomistic simulations reveal multiple and comp lex kink mechanisms of dislocation translation; however, this complexity ca n be rationalized through the analysis of a straight kink-free dislocation, based on symmetry-breaking arguments. Further reduction is achieved by obs erving that the energetics of kink mechanisms is scaled by a single paramet er, the energy required to break a bond in the core. To obtain accurate val ues of this energy we perform density functional calculations that lead us to conclude that the low mobility of the 30 degrees dislocation results fro m its high bond-breaking energy. Armed with the knowledge of kink mechanism s, we develop a kinetic Monte Carlo model that makes direct use of the atom istic data as the material-defining input and predicts the dislocation velo city on the length and time scales accessible to experiments. This provides the connection between the atomistic aspects of the dislocation core and t he mobility behaviour of single dislocations.