[gmx-users] umbrella curve

[parto haghighi]

Dear gmx users
I have done umbrella sampling for a membrnae drug system and i have
used 13 windows in this process but at last when I extracted the
histogram curve I only had two peak.Is this reasonable?
Also  my PMF curve has several minimum and maximum points and at last
it converges to zero.Is it true to report the difference of minimum
and maximum points as the gibbs free energy value?