The temperature dependent diffusion coefficient
One of the hallmarks of the BW theory is that the diffusion
coefficient itself is highly temperature dependent. At
high temperatures D follows a Ferry law typical of glasses:
D(T,n) = Doexp{-b2DE(n)2}
Here, DE(n)2 is the local mean square fluctuation in energy.
At temperatures from Tg to 2Tg the following expression
D(T,n) = Doexp{-S(n) + [bg(n)2 - b2 ] DE(n)2}
Here S(n) is the statistical entropy. The glass transition is
defined as Tg = DE(n)/[2S(n)]1/2 .
At Tg, D(Tg,n) = Dexp{-S(n)}. The diffusion coefficient
is reduced by a factor equal to the total number of configuration
states giving rise to a Levinthal paradox.