CHARMM36 forcefield.itp vs local installation

User discussions
1

GROMACS version: 2023.3 (and 2024.1)
GROMACS modification: Yes

When I’ve previously run simulation generated by CHARMM-GUI, I have always used the forcefield.itp file with the CHARMM36 GROMACS port. However, I also have CHARMM36 installed in my local GROMACS repository (with modifications to lipid.rtp to include decanoic acid). When I’m running simulations on membranes from memgen, I have been using the forcefield.itp file from older charmm-gui simulations, but I’m not sure if there is a better way to incorporate my native charmm36 force field (ex. adding the path to my topol.top file)- does anyone have advice or feedback on how to do this (or if I am ok to proceed with the forcefield.itp)? Thank you so much in advance!

2

If you want to be certain about it, then as you say, you can always add the absolute path to your forcefield.itp. If you have two versions, and one is in your current directory, then gmx pdb2gmx will usually ask you to choose, but once you have a pre-made topology, the best you can do is change the include path.

3

Thank you so much!! I’ll play around with that now!