# Missing par\_all36\_lipid.itp and par\_all36\_cgenff.itp files in CHARMM-GUI GROMACS outputs

**URL:** <https://gromacs.bioexcel.eu/t/missing-par-all36-lipid-itp-and-par-all36-cgenff-itp-files-in-charmm-gui-gromacs-outputs/12705>\
**Category:** User discussions\
**Created:** [September 29, 2025, 7:44am UTC](https://gromacs.bioexcel.eu/t/missing-par-all36-lipid-itp-and-par-all36-cgenff-itp-files-in-charmm-gui-gromacs-outputs/12705 "2025-09-29T07:44:10Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![smylmz](https://avatars.discourse-cdn.com/v4/letter/s/cab0a1/32.png) [@smylmz](https://gromacs.bioexcel.eu/u/smylmz)\
**Post date:** [September 29, 2025, 7:44am UTC](https://gromacs.bioexcel.eu/t/missing-par-all36-lipid-itp-and-par-all36-cgenff-itp-files-in-charmm-gui-gromacs-outputs/12705/1 "2025-09-29T07:44:10Z")

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have been building lipid bilayer systems (POPC, POPE, etc.) using the CHARMM-GUI Membrane Builder and downloading the **GROMACS** formatted output. However, in all of my downloads the files  
`toppar/par_all36_lipid.itp` and `toppar/par_all36_cgenff.itp` are missing from the `toppar` directory.

I have tried multiple times, selecting different lipids and system sizes, and I always download from the “GROMACS” tab at Step 5. The topology file (`topol.top`) still contains `#include` lines for these .itp files, so `grompp` fails with a “No such file or directory” error.

Could you please clarify:

- Should these `.itp` files still be generated for GROMACS outputs, or have they been replaced by other files (e.g. `.str`)?

- If they are no longer generated, what is the recommended way to include the CHARMM36 lipid parameters in GROMACS?

- Is there a direct download link or a current port of CHARMM36 lipid parameters for GROMACS that includes these `.itp` files?

Thank you very much for your help.

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**Author:** ![Marius](https://avatars.discourse-cdn.com/v4/letter/m/ed655f/32.png) [@Marius](https://gromacs.bioexcel.eu/u/Marius)\
**Post date:** [September 29, 2025, 11:29am UTC](https://gromacs.bioexcel.eu/t/missing-par-all36-lipid-itp-and-par-all36-cgenff-itp-files-in-charmm-gui-gromacs-outputs/12705/2 "2025-09-29T11:29:45Z")

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Hi @smylmz ,

the CHARMM-GUI provides you only a sub-set of the CHARMM force field with only the (non-)bonded interactions that you need for your system (i.e., forcefield.itp). The .itp files for the lipids are located in the toppar directory (e.g., POPC.itp). The topol.top should already include all those files correctly with the respective “#include …” statements. You can find a comprehensive collection of the CHARMM force field ported for GROMACS [here](https://mackerell.umaryland.edu/charmm_ff.shtml#gromacs).

Best,

Marius