Separation of diffusive jump motion and trapped motion of atoms in a glass forming process via molecular dynamics simulation

摘要

We have carried out the molecular dynamics (MD) simulation for a binary soft-sphere system and calculated the self part of the generalized susceptibility X_s (q, omega ) at various temperatures. At higher temperatures in liquid state, only one peak appears in the imaginary part of X_s, which tends to split into two peaks, the so-called alpha - and beta - peaks, as the temperature is reduced. The temperature dependence of the peak frequency is well described by the Vogel-Fulcher law for the alpha - peak, and the peak frequency does not change much for the beta - peak. We have also measured to trajectory volume of a tagged atom V(t), which is related to the dynmaical order parameter, the "generalized capacity", in structural glass transitions recently proposed by J.F.Douglas. These results show the transition temperature which is in good agreement with that determined by the trapping diffusion model.