# Error in ion.mdp command

**URL:** <https://gromacs.bioexcel.eu/t/error-in-ion-mdp-command/9321>\
**Category:** User discussions\
**Created:** [June 6, 2024, 9:15am UTC](https://gromacs.bioexcel.eu/t/error-in-ion-mdp-command/9321 "2024-06-06T09:15:25Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Rubha](https://avatars.discourse-cdn.com/v4/letter/r/b2d939/32.png) [@Rubha](https://gromacs.bioexcel.eu/u/Rubha)\
**Post date:** [June 6, 2024, 9:15am UTC](https://gromacs.bioexcel.eu/t/error-in-ion-mdp-command/9321/1 "2024-06-06T09:15:25Z")

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GROMACS version:  
GROMACS modification: Yes/No  
While performing ions.mdp command  
“gmx\_mpi grompp -f ions.mdp -c solv.gro -p topol.top -o ions.tpr”

i have recieved following error,  
ERROR 1 [file UNK.prm, line 71]:  
Encountered a second block of parameters for dihedral type 9 for the same  
atoms, with either different parameters and/or the first block has  
multiple lines. This is not supported.

ERROR 2 [file UNK.prm, line 72]:  
Encountered a second block of parameters for dihedral type 9 for the same  
atoms, with either different parameters and/or the first block has  
multiple lines. This is not supported.

how to rectify it

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**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:** [June 6, 2024, 12:17pm UTC](https://gromacs.bioexcel.eu/t/error-in-ion-mdp-command/9321/2 "2024-06-06T12:17:56Z")

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Your ligand topology specifies dihedral parameters for a torsion that is already part of the force field. That means you generated the topology with a CGenFF version that differs from what is in the force field.

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<div class="post-metadata">

**Author:** ![Rubha](https://avatars.discourse-cdn.com/v4/letter/r/b2d939/32.png) [@Rubha](https://gromacs.bioexcel.eu/u/Rubha)\
**Post date:** [June 10, 2024, 1:34pm UTC](https://gromacs.bioexcel.eu/t/error-in-ion-mdp-command/9321/3 "2024-06-10T13:34:32Z")

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So what is the possibility of solving this error

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<div class="post-metadata">

**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:** [June 10, 2024, 2:07pm UTC](https://gromacs.bioexcel.eu/t/error-in-ion-mdp-command/9321/4 "2024-06-10T14:07:01Z")

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You need to use a consistent CGenFF version. You haven’t provided us with any meaningful information about how you generated the topology, which CGenFF version you’re using (in that topology and/or in the CHARMM36 port that supports it), so there’s nothing else anyone can tell you. Force field versions have to be consistent.