# Build the Topology (adding .prm and .itp)

**URL:** <https://gromacs.bioexcel.eu/t/build-the-topology-adding-prm-and-itp/9567>\
**Category:** User discussions\
**Tags:** topology\
**Created:** [July 4, 2024, 2:21am UTC](https://gromacs.bioexcel.eu/t/build-the-topology-adding-prm-and-itp/9567 "2024-07-04T02:21:37Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![silver\_byeol](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@silver\_byeol](https://gromacs.bioexcel.eu/u/silver_byeol)\
**Post date:** [July 4, 2024, 2:21am UTC](https://gromacs.bioexcel.eu/t/build-the-topology-adding-prm-and-itp/9567/1 "2024-07-04T02:21:37Z")

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GROMACS version: 2021.2  
GROMACS modification: Yes/No  
Here post your question

Hello.  
I am trying to calculate Molecular Dynamics for protein-ligand using GROMACS/CHARMM force-field.  
I have a question…!  
I’m trying to add a parameter file for the ligand to the topol.top file (like #include ~).  
In this case, should I use both .itp and .prm? or Is it okay if I just use .itp? (Can I exclude .prm?)

The reason I am asking this question is because the following situation has occurred …

1. Create .itp and .prm files using acpype
2. and I added each fileto topol.top
3. but an error occurred when I entered the command line (gmx grompp -f ions.mdp -c solv.gro –p topol.top -o ions.tpr)
4. The error message is as follows; .prm & too few parameters on line  
Or Trying to add Buck.ham (SR) while the default nonbond type is LJ (SR)

This may be a stupid question to some, but I would appreciate it if you could let me know…!  
Thanks.

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**Author:** ![alexmathew](https://avatars.discourse-cdn.com/v4/letter/a/f4b2a3/32.png) [@alexmathew](https://gromacs.bioexcel.eu/u/alexmathew)\
**Post date:** [July 4, 2024, 2:30am UTC](https://gromacs.bioexcel.eu/t/build-the-topology-adding-prm-and-itp/9567/2 "2024-07-04T02:30:39Z")

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Kyle,  
Why you using acpype for charmm? use charmm-gui.

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**Author:** ![silver\_byeol](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@silver\_byeol](https://gromacs.bioexcel.eu/u/silver_byeol)\
**Post date:** [July 4, 2024, 2:44am UTC](https://gromacs.bioexcel.eu/t/build-the-topology-adding-prm-and-itp/9567/3 "2024-07-04T02:44:08Z")

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This is because I am cautious about uploading the structure to the web and want to proceed locally.  
Is there a way to create parameters locally other than acpype?

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**Author:** ![MagnusL](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/magnusl/32/2380_2.png) [@MagnusL](https://gromacs.bioexcel.eu/u/MagnusL)\
**Post date:** [July 4, 2024, 9:16am UTC](https://gromacs.bioexcel.eu/t/build-the-topology-adding-prm-and-itp/9567/4 "2024-07-04T09:16:02Z")

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You could try [GROMACS / STaGE · GitLab](https://gitlab.com/gromacs/stage), but it requires open babel and MATCH (to generate CGenFF/CHARMM compatible topologies) and/or ACPYPE and antechamber (for GAFF/Amber compatible topologies).