# Syntax Error in a forcefield.itp

**URL:** <https://gromacs.bioexcel.eu/t/syntax-error-in-a-forcefield-itp/1070>\
**Category:** User discussions\
**Created:** [November 10, 2020, 10:44pm UTC](https://gromacs.bioexcel.eu/t/syntax-error-in-a-forcefield-itp/1070 "2020-11-10T22:44:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![js10230](https://avatars.discourse-cdn.com/v4/letter/j/fbc32d/32.png) [@js10230](https://gromacs.bioexcel.eu/u/js10230)\
**Post date:** [November 10, 2020, 10:44pm UTC](https://gromacs.bioexcel.eu/t/syntax-error-in-a-forcefield-itp/1070/1 "2020-11-10T22:44:38Z")

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GROMACS version: 2018.3  
GROMACS modification: No

I am running simulations with 6 copies of the same peptides to create a hexamer.

When I try to make a .tpr file to add ions to the system by _gmx grompp -f ions.mdp -c cubic.gro -p topol.top -o ion.tpr_, I get the following error: (I am using CHARM36m FF)

_Fatal error:_  
_Syntax error - File forcefield.itp, line 12_  
_Last line read:_  
_‘1 2 yes 1.0 1.0’_  
_Found a second defaults directive._

I got no such error when I ran simulations for just a monomer. Do you have any idea about what might be the problem with the forcefield file? Thank you.

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**Author:** ![alevilla](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alevilla/32/439_2.png) [@alevilla](https://gromacs.bioexcel.eu/u/alevilla)\
**Post date:** [November 11, 2020, 8:25am UTC](https://gromacs.bioexcel.eu/t/syntax-error-in-a-forcefield-itp/1070/2 "2020-11-11T08:25:50Z")

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Hi,  
it looks like that you include twice the CHARMM force field. you can check your topology file (topol.top). Going from1 peptide to 6 peptide the main change is in the [molecules] part of the topol.top.  
Best regards  
Alessandra

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<div class="post-metadata">

**Author:** ![js10230](https://avatars.discourse-cdn.com/v4/letter/j/fbc32d/32.png) [@js10230](https://gromacs.bioexcel.eu/u/js10230)\
**Post date:** [November 11, 2020, 4:38pm UTC](https://gromacs.bioexcel.eu/t/syntax-error-in-a-forcefield-itp/1070/3 "2020-11-11T16:38:01Z")

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Hi,

Thank you for the reply! I looked through the .itp files for all the six peptides, and found out that there were lines for forcefield.itp. I removed them and it works fine now.

Thank you,  
Joseph

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**Author:** ![Rera](https://avatars.discourse-cdn.com/v4/letter/r/c6cbf5/32.png) [@Rera](https://gromacs.bioexcel.eu/u/Rera)\
**Post date:** [May 21, 2022, 3:22am UTC](https://gromacs.bioexcel.eu/t/syntax-error-in-a-forcefield-itp/1070/4 "2022-05-21T03:22:02Z")

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I am running simulations for protein and ligand. I have the same error. Can you guide me?

Thank you