# Umbrella Sampling Error in the Transformation Reaction Coordinate **URL:** \ **Category:** User discussions\ **Created:** [September 22, 2022, 12:47pm UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-error-in-the-transformation-reaction-coordinate/4835 "2022-09-22T12:47:18Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Bratin](https://avatars.discourse-cdn.com/v4/letter/b/f07891/32.png) [@Bratin](https://gromacs.bioexcel.eu/u/Bratin)\ **Post date:** [September 22, 2022, 12:47pm UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-error-in-the-transformation-reaction-coordinate/4835/1 "2022-09-22T12:47:18Z")
GROMACS version: Gromacs 2022.2 GROMACS modification: Yes/No Dear all, I am using transformation reaction co-ordinates to perform umbrella sampling of a rare event. I have used two reaction co-ordinates and transformed them using transformation utility of Gromacs. While doing ‘gmx wham’ I ended up with following error: Fatal error: Part1/umbrella17.tpr: Pull coordinate 1 has force constant of of 0. That doesn’t seem to be an Umbrella tpr. Please help to solve this problem. ---
**Author:** ![hess](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/hess/32/416_2.png) [@hess](https://gromacs.bioexcel.eu/u/hess)\ **Post date:** [September 23, 2022, 10:45am UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-error-in-the-transformation-reaction-coordinate/4835/2 "2022-09-23T10:45:16Z")
Did you supply a pull coordinate selection with -is? If not, I guess you need to do that. If you did, you probably provided a wrong selection. ---
**Author:** ![Bratin](https://avatars.discourse-cdn.com/v4/letter/b/f07891/32.png) [@Bratin](https://gromacs.bioexcel.eu/u/Bratin)\ **Post date:** [September 23, 2022, 4:44pm UTC](https://gromacs.bioexcel.eu/t/umbrella-sampling-error-in-the-transformation-reaction-coordinate/4835/3 "2022-09-23T16:44:40Z")
Thanks for the help