[gmx-users] Umbrella sampling - decomposing of free energy

gozde ergin gozdeeergin at gmail.com
Fri Jul 17 17:55:21 CEST 2015

Dear gromacs users,

I did umbrella sampling in order to estimate the PMF profile of my system.
My system has 512 water molecules covered by 25 decanol molecules on both
I pulled a water molecule bulk water to organic layer and than gas phase.
(Please see the system pic , http://imgur.com/sFFlVjF )

As a next step I wanted decompose this free energy in enthalpic and
entropic contribution
Delta G = Delta H - T Delta S

Enthalpies ΔH were computed by averaging the potential energy over the
respective simulation trajectory in each window (see the pic
http://imgur.com/tc3cO95 )

My question is as you see there is big variation in enthalpy.
What should I do to get more precise (less varied) potential energy?

Simulation time 4 ns, time step is 2 fs, force field os GAFF (produced by
As an example here one of the window potential energy

Thanks in advance

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