Molecule-molecule pair potentials including the internal atomic structure of the molecule

Dear All,
I am a new LAMMPS user and need helps from generous experts on how to use.
I am trying to simulate CH4 system with LAMMPS. I know how to do that with lj potential
between methane molecules as point particles. I want to do little better than this, i.e.,
I want to include the effects of internal atomic structure of CH4 which is assumed to be rigid,
which has been done in Bounds paper(J. Chem. Phys. 72, 5348),
Murad paper(Mol. Phys. 37, 725(1979)) and many others.
Any suggestions are welcome.

You have to be more specific in your questions.

Please keep in mind that this is a forum dedicated to “technical” problems with LAMMPS, not a replacement for talking to an adviser or tutor or learning MD or force fields or similar.

Methane is rather trivial to model with a large variety of molecular force fields. I am certain that you can easily find some tutorials showing you how to do simulations of methane with some MD software (not necessarily LAMMPS, but likely also including LAMMPS) and then it is just a question of translating the geometry, topology, and force field parameters.