Coherent motion of interstitial defects in a crystalline material

Thermally activated Brownian motion of interstitial defects is one of the factors driving the evolution of microstructure of crystalline metals under irradiation. In the limit of relatively small system size the motion of defects can be followed on the atomistic scale by using molecular dynamics. However, understanding the kinetics of evolution of microstructure requires investigating how defects migrate and interact on a scale which is substantially greater than that accessible to molecular dynamics. This paper shows how mobile interstitial defects can be described by quasiparticle solutions of the multistring Frenkel-Kontorova (MSFK) model, which prove the equivalence between the crowdion and the glissile dislocation loop representations of small interstitial clusters. An exact solution of the MSFK model is found for the case of an infinite straight edge dislocation. This solution illustrates the fundamental link between the concepts of a crowdion and a dislocation in a crystalline material.