Diffusion in Lennard-Jones glasses: simulation studies of the activation parameters for collective mechanisms

We present the preliminary results of a study aiming to elucidate the question of the diffusion mechanism in metallic glasses, taking advantage of the newly introduced Activation Relaxation Technique approach which allows determining the distributions of saddle heights and site depths required for building a diffusion theory in a random material. Using standard molecular dynamics (M.D.) we calculate the activation energies corresponding to collective events observed in a Lennard-Jones (L.-J.) alloy glass. We analyze them and show that a part corresponds to Zener-like cycles of displacements associated to a defect. Using then the Activation Relaxation Technique (A.R.T.) approach we show that M.D. and A.R.T. can detect the same events, and obtain also a first approximation of the site and saddle energy distributions. We discuss the signification of our results both with respect to simulation models and to experimental results.