# Fatal error while doing Protein-ligand simulation using GROMACS 2023

**URL:** https://gromacs.bioexcel.eu/t/fatal-error-while-doing-protein-ligand-simulation-using-gromacs-2023/7515
**Category:** User discussions
**Tags:** simulation-setup
**Created:** [October 31, 2023, 11:43am UTC](https://gromacs.bioexcel.eu/t/fatal-error-while-doing-protein-ligand-simulation-using-gromacs-2023/7515 "2023-10-31T11:43:11Z")
**Posts on this page:** 1
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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: [October 31, 2023, 2:53pm UTC](https://gromacs.bioexcel.eu/t/fatal-error-while-doing-protein-ligand-simulation-using-gromacs-2023/7515/3 "2023-10-31T14:53:41Z")

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The solution to the issue with MET patching is described here:

> [@Newest CHARMM36 port for GROMACS](https://gromacs.bioexcel.eu/t/newest-charmm36-port-for-gromacs/868/14):
>
> You need to use the -ter option and interactively choose from the prompts as to which termini you want. For polypeptides, you typically want NH3+. The MET1 patch is for carbohydrates, but pdb2gmx thinks it’s the best match because it matches the MET residue name. In this case, it’s the program trying to be too smart (though there are reasons for it that are typically associated with GLY residues).

Use `-ter` and select a chemically appropriate terminus.

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