How could I only consider the Lennard-Jones interaction between g-C3N4 (which is fixed) and protein in Gromacs? I've added the LJ parameter of g-C3N4 into the ffnonbonded.itp file. I used gmx insert-molecules for g-C3N4 - protein complex modeling and got a complex.gro file. But there is a mismatch between the gro file and top file. To fix this I have to write itp file for g-C3N4 but I want ignore the internal interaction inside g-C3N4. What should I do? (I'm using GROMOS54a7 forcefiled)