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].