Problem with adding ions

User discussions
1

GROMACS version: 2025.2
GROMACS modification: Yes/No
Here post your question
I am encountering an error during adding ions step, any suggestions?
gmx grompp -f ions.mdp -c solv.gro -p topol.top -o ions.tpr
:-) GROMACS - gmx grompp, 2025.2 (-:

Executable: /usr/local/gromacs/bin/gmx
Data prefix: /usr/local/gromacs
Working dir: /mnt/c/Users/hp5cd/OneDrive/Desktop/gmx
Command line:
gmx grompp -f ions.mdp -c solv.gro -p topol.top -o ions.tpr

Ignoring obsolete mdp entry ‘title’
Ignoring obsolete mdp entry ‘ns_type’

NOTE 1 [file ions.mdp]:
With Verlet lists the optimal nstlist is >= 10, with GPUs >= 20. Note
that with the Verlet scheme, nstlist has no effect on the accuracy of
your simulation.

Setting the LD random seed to -201359444

Generated 167799 of the 167910 non-bonded parameter combinations
Generating 1-4 interactions: fudge = 1

Generated 117432 of the 167910 1-4 parameter combinations

Program: gmx grompp, version 2025.2
Source file: src/gromacs/gmxpreprocess/topio.cpp (line 723)

Fatal error:
Syntax error - File CUR.prm, line 1
Last line read:
‘[ bondtypes ]’
Invalid order for directive bondtypes

For more information and tips for troubleshooting, please check the GROMACS
website at Common errors when using GROMACS - GROMACS 2025.2 documentation

2

Hi,

The error most likely occurs because the .prm file is included at the wrong position in your .top file. This file defines new parameters—apparently bond parameters in your case—which GROMACS expects to be loaded before the [ moleculetype ] directive (if I remember correctly). Therefore, you should place the #include "CUR.prm" statement directly after the inclusion of the force field file (e.g., forcefield.itp, assuming you are using CHARMM).

Best regards,
Marius