Abstract
Quenches 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 landscape, ${U}_{m},$ decreases. Super-Arrhenius T dependence of the self-diffusion constant D, characteristic of fragile liquids, is thus a consequence of the descent of the system, with decreasing T, from a plateau of ${U}_{m}$ values at the top of the landscape. Departure from the top occurs at a random temperature ${T}_{s}$ but introduction of ${E}_{a}{(U}_{m})$ allows a systematic analysis of $D(T).$ A single quench exhibits several features of the experimental glass transition. Fast cooling in prior work has isolated the supercooled ``top'' state only. The difference between strong and fragile liquids, and the fate of the quenches, is discussed in terms of the landscape and its N dependence.
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