Dependence of supercooled liquid dynamics on elevation in the energy landscape

wQuenches of the Lennard-Jones unit density, N = 256 supercooled liquid are analyzed to show that the activation energy for diffusion, E-a, increases as the energy of the associated local minimum on the potential energy lands cape, U-m, decreases. Super-Arrhenius T dependence of the self-diffusion co nstant D, characteristic of fragile liquids, is thus a consequence of the d escent of the system, with decreasing T, from a plateau of U-m values at th e top of the landscape. Departure from the top occurs at a random temperatu re T-s but introduction of E-a( U-m) allows a systematic analysis of D(T). A single quench exhibits several features of the experimental glass transit ion. Fast cooling in prior work has isolated the supercooled "top" state on ly. The difference between strong and fragile liquids, and the fate of the quenches, is discussed in terms of the landscape and its N dependence. [S10 63-651X(99)09503-3].