# Error at adding ions

**URL:** https://gromacs.bioexcel.eu/t/error-at-adding-ions/3242
**Category:** User discussions
**Created:** [December 3, 2021, 11:10am UTC](https://gromacs.bioexcel.eu/t/error-at-adding-ions/3242 "2021-12-03T11:10:44Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![Manvi](https://avatars.discourse-cdn.com/v4/letter/m/e9c0ed/32.png) [@Manvi](https://gromacs.bioexcel.eu/u/Manvi)
#### Post date: [December 3, 2021, 11:10am UTC](https://gromacs.bioexcel.eu/t/error-at-adding-ions/3242/1 "2021-12-03T11:10:45Z")

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GROMACS version:  
GROMACS modification: Yes/No  
Here post your question  
Hi,  
pdb2gmx resulted in HIP state for His which was changed to His manually. But topol.top also needs to be modified accordingly.  
Is there any way we can modify the protein.gro and topol.top without much manual intervention.  
Thanks

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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: [December 4, 2021, 1:12pm UTC](https://gromacs.bioexcel.eu/t/error-at-adding-ions/3242/2 "2021-12-04T13:12:19Z")

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You can interactively select protonation states of titratable residues when running `pdb2gmx`.