Potential issue in gmx genion with -neutral Option for +2 Ions

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1

GROMACS version:
GROMACS modification: Yes/No
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In GROMACS 2024.3, I used gmx genion to neutralize a DNA system with -14 charge using Mg²⁺. I expected 7 Mg ions (since Mg is +2), but the program tried to add 14 ions instead.

gmx genion -s file.tpr -o file_Mg.gro -p file.top -neutral -pname MG
Is this a bug in -neutral handling for divalent ions, or am I missing something?

Thank you in advance.

2

You need to specify -pq 2 because the program assumes all ions are monovalent unless you tell it otherwise.

3

thank you so much