[gmx-users] g_wham error

Justin A. Lemkul jalemkul at vt.edu
Sat Nov 19 18:27:33 CET 2011

rajat desikan wrote:
> Hi
> I am a new gromacs user. I just completed Justin's umbrella sampling 
> tutorial. I am doing a PMF calculation between 2 methane molecules in 
> water. The simulation has run fine till the g_wham step. My command is
> -- g_wham -it tpr-files.dat -if pullf-files.dat -o -hist -unit kCal -b 2000
> I get a warning:
> WARNING, no data point in bin 2 (z=0.366256) !
> You may not get a reasonable profile. Check your histograms!
> and my histogram contains a single peak.
> I have pulled my other methane 1 nm away from the first methane. I have 
> 15 sampling windows (0.05 nm apart till 5nm and then 1 nm apart)...can 
> you please tell me how to correct this?

With 15 windows, you should have 15 histograms.  Plot with:

xmgrace -nxy histo.xvg

It will show you where the lack of sampling is.



Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


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