# Ionization Issue In Metalloprotein MD Simulation **URL:** \ **Category:** User discussions\ **Created:** [November 9, 2022, 4:22pm UTC](https://gromacs.bioexcel.eu/t/ionization-issue-in-metalloprotein-md-simulation/5218 "2022-11-09T16:22:47Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![naeemhmg](https://avatars.discourse-cdn.com/v4/letter/n/90ced4/32.png) [@naeemhmg](https://gromacs.bioexcel.eu/u/naeemhmg)\ **Post date:** [November 9, 2022, 4:22pm UTC](https://gromacs.bioexcel.eu/t/ionization-issue-in-metalloprotein-md-simulation/5218/1 "2022-11-09T16:22:47Z")
GROMACS version: 5.0.5 GROMACS modification: Yes/No I am trying for the ligand-protein docking of metalloprotein (containing zinc) with the ligand. at ionization, step using the following command gmx grompp -f ions.mdp -c solv.gro -p topol.top -o ions.tpr I am facing the following issue. ![image](https://europe1.discourse-cdn.com/flex017/uploads/bioexcel1/original/2X/0/0f06db2e7598bcd64d6b501b137d9feda8cc61e6.png) Can you please help me to sort out this issue please? Currently, we are using charmm36 forcefield. ---
**Author:** ![alexnas](https://dub1.discourse-cdn.com/flex017/user_avatar/gromacs.bioexcel.eu/alexnas/32/1826_2.png) [@alexnas](https://gromacs.bioexcel.eu/u/alexnas)\ **Post date:** [November 15, 2022, 9:24am UTC](https://gromacs.bioexcel.eu/t/ionization-issue-in-metalloprotein-md-simulation/5218/2 "2022-11-15T09:24:37Z")
This thread might be helpful: > [@Atomtype Cu2+ not found](https://gromacs.bioexcel.eu/t/atomtype-cu2-not-found/1321): > > GROMACS version: 5.2 GROMACS modification: Yes/No Hi, I have a problem; I built a simulation box with a slab of graphene in the middle of the box, filled with water on one side and saline (NaCl) on other side. I have checked the executable files (.gro, .itp, topol , …) several times and they are correct , but I give this error : atomtype Cu2+ not found. Does anyone have any experience to share with me?