MOLECULAR-DYNAMICS SIMULATIONS OF SUPERCOOLED LIQUIDS NEAR THE GLASS-TRANSITION

Relaxation phenomena at microscopic length scales have been studied in a model supercooled liquid by molecular dynamics (MD) simulations. In spite of its obvious limitations (large cooling rates, small timescales), the MD method provides useful tests of the theoretical predictions for simple systems: in the soft sphere system investigated, a transition characterized by a sudden change in the self-diffusion mechanism was unambiguously identified. This transition is likely related to the ergodic-non-ergodic transition predicted by mode coupling theories. The relaxation functions for microscopic density-density correlations exhibit the stretching and scaling properties characteristic of supercooled liquids in the glass transition range. Some non-trivial predictions of mode coupling theories for the shape and scaling properties of these relaxation functions have been tested, resulting in a qualitative agreement.