RMSD analysis of the Protein-Ligand simulation

GROMACS version: 2023.2
GROMACS modification: Yes/No
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Hey , I hope everythings fine. I had query regarding the Index file preparation using gromacs command gmx make_ndx. after successfull running of the command what group should we select for index file preparation either its individual groups protein and UNK or its Protein_Ligand (merged form).