Mobility and diffusivity in a generalized Frenkel-Kontorova model

Molecular dynamics simulations are used to investigate the atomic mobility and diffusivity of a generalized Frenkel-Kontorova model which takes into account anharmonic (exponential) interaction of atoms subjected to a three-dimensional substrate potential periodic in two dimensions and nonconvex (Morse) in the third dimension. The numerical results are explained by a phenomenological theory which treats a system of strongly interacting atoms as a system of weakly interacting quasiparticles (kinks). Model parameters are chosen close to those for the K-W(112) adsorption system.