
Depiction of a free energy barrier in South African physical chemist Adriaan De Lange's 2001 discussion of human free energy landscape in the evolutionary-perspective, employing a mixture of chaos theory, Prigoginean bifurcation theory, order-disorder logic, time (past vs future), path functions, and discussions of high and low values of entropy change. [1]

Depiction of a free energy barrier in South African physical chemist Adriaan De Lange's 2001 discussion of human free energy landscape in the evolutionary-perspective, employing a mixture of chaos theory, Prigoginean bifurcation theory, order-disorder logic, time (past vs future), path functions, and discussions of high and low values of entropy change. [1]

In thermodynamics, free energy barrier refers to a heightened state of free energy, typically Gibbs free energy, of the various possible conformations or paths of one or more molecular entities. The term free energy barrier, used frequently in discussions of energy landscapes, seems, in most cases to be a synonym of activation energy or "activation energy barrier", although there do seem to be similarities and more investigation of the subtlety differences between the two terms is in order.

References
1. De Lange, A.M. (2001). “Fitness Landscape and other Landscapes” (threads: LO27222), 09/03/01 – Learning-org.com.

Further reading
● Vehkamaki, Hanna. (2006). Classical Nucleation Theory in Multicomponent Systems (3.11: Free energy barrier in the Ising model, pgs. 67-). Birkhauser.
● Wanasundara, Surajith N. and Thachuk, Mark. (2009). “Free Energy Barrier Estimation for Dissociation of Charged Protein Complexes in the Gas Phase” (abstract), J. Phys. Chem. A. 113(16): 3814-3821.