# Enforced Rotation - Fatal Error message **URL:** \ **Category:** User discussions\ **Created:** [June 27, 2020, 9:33pm UTC](https://gromacs.bioexcel.eu/t/enforced-rotation-fatal-error-message/388 "2020-06-27T21:33:13Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![masaw](https://avatars.discourse-cdn.com/v4/letter/m/e56c9b/32.png) [@masaw](https://gromacs.bioexcel.eu/u/masaw)\ **Post date:** [June 27, 2020, 9:33pm UTC](https://gromacs.bioexcel.eu/t/enforced-rotation-fatal-error-message/388/1 "2020-06-27T21:33:14Z")
GROMACS version: 2020.2 GROMACS modification: No Here post your question I have tried to use the enforced rotation approach to rotate the N-terminal Domain of the solvated protein. Then, I have received the following error message: Fatal error: Number of atoms in file rotref.0.trr (180116) does not match the number of atoms in rotation group (152)! Any suggestions? I have been used the following mdp commands: ; Enforced rotation: No or Yes rotation = Yes ; Output frequency for angle, torque and rotation potential energy for the whole group rot-nstrout = 10 ; Output frequency for per-slab data (angles, torques and slab centers) rot-nstsout = 10 ; Number of rotation groups rot-ngroups = 1 ; Rotation group name rot-group0 = TM\_A\_TM\_B ; Rotation potential. Can be iso, iso-pf, pm, pm-pf, rm, rm-pf, rm2, rm2-pf, flex, flex-t, flex2, flex2-t rot-type0 = iso-pf ; Use mass-weighting of the rotation group positions rot-massw0 = yes ; Rotation vector, will get normalized rot-vec0 = 0 0 1 ; Rotation rate [degree/ps] and force constant [kJ/(mol_nm^2)] rot-rate0 = 10.0 rot-k0 = 500.0 ; Rotation rate [degree/ps] and force constant [kJ/(mol_nm^2)] rot-rate0 = 10.0 rot-k0 = 500.0 ; Slab distance for flexible axis rotation [nm] rot-slab-dist0 = 1.5 ; Minimum value of Gaussian function for the force to be evaluated (for flex\* potentials) rot-min-gauss0 = 0.001 ; Value of additive constant epsilon’ [nm^2] for rm2\* and flex2\* potentials rot-eps0 = 0.0001 ; Fitting method to determine angle of rotation group (rmsd, norm, or potential) rot-fit-method0 = norm ; For fit type ‘potential’, nr. of angles around the reference for which the pot. is evaluated rot-potfit-nsteps0 = 21 ; For fit type ‘potential’, distance in degrees between two consecutive angles rot-potfit-step0 = 0.25 What did I do wrong here? Any suggestions? Thank you in advance. Masa ---
**Author:** ![avilla](https://avatars.discourse-cdn.com/v4/letter/a/f1d935/32.png) [@avilla](https://gromacs.bioexcel.eu/u/avilla)\ **Post date:** [June 29, 2020, 2:22pm UTC](https://gromacs.bioexcel.eu/t/enforced-rotation-fatal-error-message/388/2 "2020-06-29T14:22:09Z")
I have no experience with the option you are using, but the error is telling you that “the reference rotref.0.trr contains all the atoms while the program is expecting to find only the rotation group” You could try to let grompp to generate trr file for you ( see usage in [http://manual.gromacs.org/documentation/current/reference-manual/special/enforced-rotation.html?highlight=usage%20](http://manual.gromacs.org/documentation/current/reference-manual/special/enforced-rotation.html?highlight=usage%20) ) thus you can check what format trr should have. ---
**Author:** ![Carsten](https://avatars.discourse-cdn.com/v4/letter/c/f14d63/32.png) [@Carsten](https://gromacs.bioexcel.eu/u/Carsten)\ **Post date:** [July 17, 2020, 8:26am UTC](https://gromacs.bioexcel.eu/t/enforced-rotation-fatal-error-message/388/3 "2020-07-17T08:26:42Z")
Hi, I would guess that you simply have some (old) rotref.0.trr lying around in the directory where you called grompp. If you have no special requirements for the rotation reference file, you can use the initial positions of the rotation group. This will be automatically done if no rotref.0.trr file is found. So deleting/moving that file from the directory where you call grompp should resolve that issue. Best, Carsten ---
**Author:** ![masaw](https://avatars.discourse-cdn.com/v4/letter/m/e56c9b/32.png) [@masaw](https://gromacs.bioexcel.eu/u/masaw)\ **Post date:** [July 17, 2020, 2:42pm UTC](https://gromacs.bioexcel.eu/t/enforced-rotation-fatal-error-message/388/4 "2020-07-17T14:42:38Z")
Thank you very much for the suggestion. Yes, gromacs could not find the proper trr file, which just contains the rotational group. ---
**Author:** ![masaw](https://avatars.discourse-cdn.com/v4/letter/m/e56c9b/32.png) [@masaw](https://gromacs.bioexcel.eu/u/masaw)\ **Post date:** [July 17, 2020, 2:43pm UTC](https://gromacs.bioexcel.eu/t/enforced-rotation-fatal-error-message/388/5 "2020-07-17T14:43:19Z")
Thank you for the suggestion. It is working now. Again, thanks.