Very nice example of using PyMC3 (and pm.Potential) to simulate physical systems!
I think one nice extension to your example will be to include a “kT- term” and suggest the student/user to test values like 0.1, 1 and 10 to explore the role of temperature in the system.
Regarding @aseyboldt comment I want to add that I am using PyMC3 with the SMC sampler to simulate (small) biomolecules with very good results so far 
Maybe the energy barrier in your example is relatively low, but for the systems I am using SMC is crucial to avoid getting trapped in local minima.