Potential energy difference with different force fields

Dear LAMMPS users,

I am modeling a simple 2D Graphitic Carbon Nitride (g-C3N4) nanosheet with 54 atoms. I used several force fields with both LAMMPS and GROMACS and the potential energies of the system in npt at 1K and 1 atmosphere are:

  1. LAMMPS using ffield.reax.CHOSFCl = -6,024 Kcal/mol

  2. LAMMPS using tersoff = -7,148 Kcal/mol

  3. LAMMPS using ATB server - gromos54a7 forcefield = -270 Kcal/mol

  4. GROMACS: using ATB server - gromos54a7 forcefield = -228 Kcal/mol

We know that the zero of the potential energy is not the same for all the force fields but is it usual to be an order of magnitude difference between REAX and GROMOS force fields?

P.S. All the force fields were recommended and used by the literature for the g-C3N4.

the absolute value of the total energy is completely arbitrary, thus you cannot compare absolute values.