Dear all GROMACS users,

I'm now trying to be familiar with GROMACS, since I found that it is faster than LAMMPS.

I started to run examples on : https://www.svedruziclab.com/tutorials/gromacs/2-methane-in-water/

But in LAMMPS, I've used modified LJ parameters manually on script using pair_coeff command, but I can't figure out how to do this on GROMACS.

For example, I made methane.rtp file, and used OPLS-AA forcefield by using opls_138 and opls_140 atom types. Also I used TIP4P-EW water model. But in some papers, methane-water interaction parameters are modified to increase solubility of methane in water.

So, I want to modify the epsilon between methane and water, but how can I do this?