Please provide very much more information. Unless somebody has run into the exact thing that you are describing it is currently impossible for us to help you.

One thing I can suggest now is to construct histograms of the sampling from the coord.xvg files yourself with some scripting and plot them all together to see if you have some regions with no overlap (but even still, please address my first point).

-- original message --

Hi all:

I have been trying to figure out a problem in our umbrella sampling simulation. We are simulating a coarse grained protein passing through a coarse grained lipid bilayer. In the pull simulation, the protein was made to move from +z=6 nm of the box through the lipid layer at z=0 to z= -4 nm. For umbrella sampling 74 windows where chosen with a 0.2 nm. When we look at the histogram from the g_wham, we get good overlap before the protein touches the bilayer and after it has exited the bilayer. We also get the PMF curves for these regions.

However, when the the protein is in contact, and barely touching the bilayer, the g_wham analysis gives 0.000E+0 for PMF and no histograms in the output. We have tried decreasing the window size from 0.2 to 0.1 nm but it does not help.

I looked at the gmx-user list to find a possible solution to this issue but could not find any helpful clue. Could anyone point me to what should be done and what is possibly going wrong?

Thanks,
SNC
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