Freezeing molecular structure in MM calculations

Questions
#1

Dear users and developers

Is it possible in the MM (force field) calculations to freeze the molecular geometry of one molecule, retaining the flexibility of the rest of the system (which is non-covalently bonded to the frozen molecule)?

Is the FIXED option in the $opt section appropriate in this case? I tried it in the QM/MM geometry optimization to fix the QM part structure, but the program writes in the output “number of fixed atoms 0”

I will be grateful for any assistance.
Yours sincerely
Marcin Andrzejak

#2

I do not think this is possible. You would be better off running Q-Chem-based QM/MM through an interface to a good MD program. Interfaces to Q-Chem exist for CHARMM, Gromacs, and maybe Amber.