Thermally activated mobility of clusters of interstitial atoms is an important factor driving microstructural evolution of materials under irradiation. Molecular dynamics simulations show that the statistics of one-dimensional Brownian motion of clusters is characterized by unusual correlated jumps spanning many interatomic distances. We use the Frenkel-Kontorova model to investigate the dynamics of one-dimensional Brownian motion of a spatially delocalized interstitial defect interacting with acoustic phonon excitations. Using a quantum-mechanical approach, we evaluate the coefficient of dissipative friction characterizing the stochastic motion of the defect. We show that the origin of unusual features observed in atomistic simulations is associated with low friction experienced by an interstitial defect propagating through the crystal lattice in the presence of thermal fluctuations. We also find that the coefficient of dissipative friction is highly sensitive to the character of interatomic bonding in the material.

• Received 5 April 2001

DOI:https://doi.org/10.1103/PhysRevB.65.224105