# For two ligand and a complex molecular dynamics simulation in GROMACS

**URL:** <https://gromacs.bioexcel.eu/t/for-two-ligand-and-a-complex-molecular-dynamics-simulation-in-gromacs/9880>\
**Category:** User discussions\
**Tags:** grompp, mdrun, gmx-grompp\
**Created:** [August 14, 2024, 1:56pm UTC](https://gromacs.bioexcel.eu/t/for-two-ligand-and-a-complex-molecular-dynamics-simulation-in-gromacs/9880 "2024-08-14T13:56:24Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Kirtiman07](https://avatars.discourse-cdn.com/v4/letter/k/ce7236/32.png) [@Kirtiman07](https://gromacs.bioexcel.eu/u/Kirtiman07)\
**Post date:** [August 14, 2024, 1:56pm UTC](https://gromacs.bioexcel.eu/t/for-two-ligand-and-a-complex-molecular-dynamics-simulation-in-gromacs/9880/1 "2024-08-14T13:56:24Z")

</div>

Program: gmx genion, version 2020.1-Ubuntu-2020.1-1  
Source file: src/gromacs/gmxpreprocess/genion.cpp (line 155)

Fatal error:  
No more replaceable solvent!

so how can i over come this problem.  
this error is showing when i input the ionisation command

GROMACS version:2020.1  
GROMACS modification: Yes/No  
Here post your question

---

<div class="post-metadata">

**Author:** ![mHijazi](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/mhijazi/32/5108_2.png) [@mHijazi](https://gromacs.bioexcel.eu/u/mHijazi)\
**Post date:** [August 14, 2024, 3:13pm UTC](https://gromacs.bioexcel.eu/t/for-two-ligand-and-a-complex-molecular-dynamics-simulation-in-gromacs/9880/2 "2024-08-14T15:13:29Z")

</div>

The error message is telling you that you’re trying to replace solvent molecules (usually water) with a solute or other molecules, but the program has run out of solvent molecules to replace.

Double check that you are selecting the solvent when running the genion command

If you are indeed choosing the solvent, then check the box size, you may not have enough solvent molecules, and then check the ion concentration you’re requesting, it may be too high (usually a concentration of 0.1 or 0.15 should do the trick, but it depends on your simulation setup!)

---

<div class="post-metadata">

**Author:** ![Kirtiman07](https://avatars.discourse-cdn.com/v4/letter/k/ce7236/32.png) [@Kirtiman07](https://gromacs.bioexcel.eu/u/Kirtiman07)\
**Post date:** [August 15, 2024, 7:34am UTC](https://gromacs.bioexcel.eu/t/for-two-ligand-and-a-complex-molecular-dynamics-simulation-in-gromacs/9880/3 "2024-08-15T07:34:52Z")

</div>

Thank you so much Mr. mHijazi sir for your valuable comment.