Hi Noam,
The original files I attached earlier contained no constraints (fixed atoms or intramolecular).
What I have noticed is that for AD_LANGEVIN thermostat with:
1) REGION GLOBAL: Does not work in QM, MM or QM/MM system (with or without constraints). For pure QM, no constraints (H2O-32.inp) I get a cholesky decomposition error which is gone once I change the thermostat settings.
2) REGION MASSIVE: Fully functional.
Since we need to use a global thermostat for fixed atoms, so effectively AD_LANGEVIN doesn't seems to work with constraints and/or REGION GLOBAL thermostat setting.
Best,
Mayank