[gmx-users] g_wham giving flat free energy

Michael McGovern mpmcgovern at wisc.edu
Fri Apr 23 15:36:41 CEST 2010

Hi everyone.  I'm having some trouble using g_wham to analyze some results.  I have some simulations from gromacs 3.3 using the pull code.  I'm using the latest version of g_wham to analyze the results, which the help file says is ok, using the -ip option.  
I've gotten almost everything to work, and it generates histograms that seem perfectly reasonable, but sometimes the free energy it outputs is completely flat, with each bin having a free energy value of 0.
I've played around with the -b and -e options using only part of my data, and sometimes it gives non-flat free energies, other times not.  I see no logic to when it works and when it doesn't.  My data does have good overlap of the histograms, and it sometimes converges even when I use data that have no overlaps, so that doesn't seem to be the problem.
I'm completely confused.  Does anyone know what could cause this?

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