# Umbrella sampling does not generate PMF results **URL:** \ **Category:** User discussions\ **Created:** [November 20, 2020, 7:12pm UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-does-not-generate-pmf-results/1131 "2020-11-20T19:12:58Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![cmsuser](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@cmsuser](https://gromacs.bioexcel.eu/u/cmsuser)\ **Post date:** [November 20, 2020, 7:12pm UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-does-not-generate-pmf-results/1131/1 "2020-11-20T19:12:58Z")
GROMACS version:2018.2-gcc910 GROMACS modification: No Hi, All, I found the following problem when I do umbrella sampling calculation. When I do WHAM, it says it switched to exact iteration and the output in hist.xvg shows all the energies are zero. What could be wrong? I am doing PMF calculation of pulling two slabs of polymers apart. I imagine the force could be very large. Any comments or suggestions would be appreciated. "Wrote histo.xvg Getting initial potential by integration. Initialized rapid wham stuff (contrib tolerance 1.05263e-08) Evaluating only 4609 of 19000 expressions. ``` 1) Maximum change 2.864556e+02 100) Maximum change 7.539510e-01 200) Maximum change 7.172030e-01 300) Maximum change 1.411430e+00 ``` Switched to exact iteration in iteration 303 Converged in 304 iterations. Final maximum change 0 Wrote hist.xvg" ---
**Author:** ![jalemkul](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/jalemkul/32/18_2.png) [@jalemkul](https://gromacs.bioexcel.eu/u/jalemkul)\ **Post date:** [November 23, 2020, 2:01pm UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-does-not-generate-pmf-results/1131/2 "2020-11-23T14:01:25Z")
> [@cmsuser](#): > > When I do WHAM, it says it switched to exact iteration and the output in hist.xvg shows all the energies are zero. `hist.xvg` should have multiple histograms of positions within each window along the reaction coordinate, not energies. Do you get any overlap between these histograms? They should not be all zero, as some sampling had to occur somewhere. ---
**Author:** ![cmsuser](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@cmsuser](https://gromacs.bioexcel.eu/u/cmsuser)\ **Post date:** [November 24, 2020, 2:10pm UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-does-not-generate-pmf-results/1131/3 "2020-11-24T14:10:44Z")
My hist.xvg is actually the PMF output file. They have all zeros. The histo.xvg shows the reaction coordinates. They have decent ovelap between those histograms. The output is like this. # This file was created Fri Nov 20 11:48:34 2020 # Created by: # :-) GROMACS - gmx wham, 2018.2 (-: # # Executable: /share/apps/gromacs/2018.2/bin/gmx\_mpi # Data prefix: /share/apps/gromacs/2018.2 # Working dir: /home/\*\*/umbrella\_sampling2 # Command line: # gmx\_mpi wham -it tpr-files.dat -if pull-files.dat -o hist -unit kT # gmx wham is part of G R O M A C S: # # Good gRace! Old Maple Actually Chews Slate # @ title “Umbrella potential” @ xaxis label “\xx\f{} (nm)” @ yaxis label “E (kT)” @TYPE xy 1.520579e+00 0.000000e+00 1.545180e+00 0.000000e+00 1.569781e+00 0.000000e+00 1.594382e+00 0.000000e+00 1.618983e+00 0.000000e+00 1.643584e+00 0.000000e+00 1.668185e+00 0.000000e+00 1.692786e+00 0.000000e+00 1.717387e+00 0.000000e+00 1.741988e+00 0.000000e+00 1.766589e+00 0.000000e+00 1.791190e+00 0.000000e+00 1.815791e+00 0.000000e+00 1.840392e+00 0.000000e+00 1.864993e+00 0.000000e+00 1.889594e+00 0.000000e+00 1.914195e+00 0.000000e+00 1.938796e+00 0.000000e+00 1.963397e+00 0.000000e+00 1.987998e+00 0.000000e+00 2.012599e+00 0.000000e+00 2.037199e+00 0.000000e+00 2.061800e+00 0.000000e+00 2.086401e+00 0.000000e+00 2.111002e+00 0.000000e+00 2.135603e+00 0.000000e+00 2.160204e+00 0.000000e+00 2.184805e+00 0.000000e+00 2.209406e+00 0.000000e+00 2.234007e+00 0.000000e+00 2.258608e+00 0.000000e+00 2.283209e+00 0.000000e+00 2.307810e+00 0.000000e+00 2.332411e+00 0.000000e+00 2.357012e+00 0.000000e+00 2.381613e+00 0.000000e+00 2.406214e+00 0.000000e+00 2.430815e+00 0.000000e+00 2.455416e+00 0.000000e+00 2.480017e+00 0.000000e+00 2.504618e+00 0.000000e+00 2.529219e+00 0.000000e+00 2.553820e+00 0.000000e+00 2.578421e+00 0.000000e+00 2.603022e+00 0.000000e+00 2.627623e+00 0.000000e+00 2.652224e+00 0.000000e+00 2.676825e+00 0.000000e+00 2.701426e+00 0.000000e+00 2.726027e+00 0.000000e+00 2.750628e+00 0.000000e+00 2.775228e+00 0.000000e+00 2.799829e+00 0.000000e+00 2.824430e+00 0.000000e+00 2.849031e+00 0.000000e+00 2.873632e+00 0.000000e+00 2.898233e+00 0.000000e+00 2.922834e+00 0.000000e+00 2.947435e+00 0.000000e+00 2.972036e+00 0.000000e+00 2.996637e+00 0.000000e+00 3.021238e+00 0.000000e+00 3.045839e+00 0.000000e+00 3.070440e+00 0.000000e+00 3.095041e+00 0.000000e+00 3.119642e+00 0.000000e+00 3.144243e+00 0.000000e+00 3.168844e+00 0.000000e+00 3.193445e+00 0.000000e+00 3.218046e+00 0.000000e+00 3.242647e+00 0.000000e+00 3.267248e+00 0.000000e+00 3.291849e+00 0.000000e+00 3.316450e+00 0.000000e+00 3.341051e+00 0.000000e+00 3.365652e+00 0.000000e+00 3.390253e+00 0.000000e+00 3.414854e+00 0.000000e+00 3.439455e+00 0.000000e+00 3.464056e+00 0.000000e+00 3.488656e+00 0.000000e+00 3.513257e+00 0.000000e+00 3.537858e+00 0.000000e+00 3.562459e+00 0.000000e+00 3.587060e+00 0.000000e+00 3.611661e+00 0.000000e+00 3.636262e+00 0.000000e+00 3.660863e+00 0.000000e+00 3.685464e+00 0.000000e+00 3.710065e+00 0.000000e+00 3.734666e+00 0.000000e+00 3.759267e+00 0.000000e+00 3.783868e+00 0.000000e+00 3.808469e+00 0.000000e+00 3.833070e+00 0.000000e+00 3.857671e+00 0.000000e+00 3.882272e+00 0.000000e+00 3.906873e+00 0.000000e+00 3.931474e+00 0.000000e+00 3.956075e+00 0.000000e+00 3.980676e+00 0.000000e+00 4.005277e+00 0.000000e+00 4.029878e+00 0.000000e+00 4.054479e+00 0.000000e+00 4.079080e+00 0.000000e+00 4.103681e+00 0.000000e+00 4.128282e+00 0.000000e+00 4.152883e+00 0.000000e+00 4.177484e+00 0.000000e+00 4.202085e+00 0.000000e+00 4.226685e+00 0.000000e+00 4.251286e+00 0.000000e+00 4.275887e+00 0.000000e+00 4.300488e+00 0.000000e+00 4.325089e+00 0.000000e+00 4.349690e+00 0.000000e+00 4.374291e+00 0.000000e+00 4.398892e+00 0.000000e+00 4.423493e+00 0.000000e+00 4.448094e+00 0.000000e+00 4.472695e+00 0.000000e+00 4.497296e+00 0.000000e+00 4.521897e+00 0.000000e+00 4.546498e+00 0.000000e+00 4.571099e+00 0.000000e+00 4.595700e+00 0.000000e+00 4.620301e+00 0.000000e+00 4.644902e+00 0.000000e+00 4.669503e+00 0.000000e+00 4.694104e+00 0.000000e+00 4.718705e+00 0.000000e+00 4.743306e+00 0.000000e+00 4.767907e+00 0.000000e+00 4.792508e+00 0.000000e+00 4.817109e+00 0.000000e+00 4.841710e+00 0.000000e+00 4.866311e+00 0.000000e+00 4.890912e+00 0.000000e+00 4.915513e+00 0.000000e+00 4.940113e+00 0.000000e+00 4.964714e+00 0.000000e+00 4.989315e+00 0.000000e+00 5.013916e+00 0.000000e+00 5.038517e+00 0.000000e+00 5.063118e+00 0.000000e+00 5.087719e+00 0.000000e+00 5.112320e+00 0.000000e+00 5.136921e+00 0.000000e+00 5.161522e+00 0.000000e+00 5.186123e+00 0.000000e+00 5.210724e+00 0.000000e+00 5.235325e+00 0.000000e+00 5.259926e+00 0.000000e+00 5.284527e+00 0.000000e+00 5.309128e+00 0.000000e+00 5.333729e+00 0.000000e+00 5.358330e+00 0.000000e+00 5.382931e+00 0.000000e+00 5.407532e+00 0.000000e+00 5.432133e+00 0.000000e+00 5.456734e+00 0.000000e+00 5.481335e+00 0.000000e+00 5.505936e+00 0.000000e+00 5.530537e+00 0.000000e+00 5.555138e+00 0.000000e+00 5.579739e+00 0.000000e+00 5.604340e+00 0.000000e+00 5.628941e+00 0.000000e+00 5.653541e+00 0.000000e+00 5.678142e+00 0.000000e+00 5.702743e+00 0.000000e+00 5.727344e+00 0.000000e+00 5.751945e+00 0.000000e+00 5.776546e+00 0.000000e+00 5.801147e+00 0.000000e+00 5.825748e+00 0.000000e+00 5.850349e+00 0.000000e+00 5.874950e+00 0.000000e+00 5.899551e+00 0.000000e+00 5.924152e+00 0.000000e+00 5.948753e+00 0.000000e+00 5.973354e+00 0.000000e+00 5.997955e+00 0.000000e+00 6.022556e+00 0.000000e+00 6.047157e+00 0.000000e+00 6.071758e+00 0.000000e+00 6.096359e+00 0.000000e+00 6.120960e+00 0.000000e+00 6.145561e+00 0.000000e+00 6.170162e+00 0.000000e+00 6.194763e+00 0.000000e+00 6.219364e+00 0.000000e+00 6.243965e+00 0.000000e+00 6.268566e+00 0.000000e+00 6.293167e+00 0.000000e+00 6.317768e+00 0.000000e+00 6.342369e+00 0.000000e+00 6.366970e+00 0.000000e+00 6.391570e+00 0.000000e+00 6.416171e+00 0.000000e+00 ---
**Author:** ![gongs](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/gongs/32/2768_2.png) [@gongs](https://gromacs.bioexcel.eu/u/gongs)\ **Post date:** [August 23, 2024, 10:58am UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-does-not-generate-pmf-results/1131/4 "2024-08-23T10:58:27Z")
Hi, have you resolved this issue? I have also encountered this problem.