How to generate topology for Graphene molecule from .gro file using GROMACS program?

GROMACS version: GROMACS/2022.4-fosscuda-2020b
GROMACS modification: Yes/No
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Greetings, everybody. I have generated a graphene sheet using the VMD program and saved the resulting file in the .gro format. Now I would like to use the GROMACS program to model the interaction between graphene and a solvent. To proceed, I require the topl.top and .itp files for my graphene sheet. If feasible, I would like to immobilize or freeze the graphene atoms prior to energy minimization in the simulation to avoid the folding or transfer of the graphene atoms. If somebody has developed such system, please guide me. I will be highly thankful to you.