Hello, I am a new user of QChem and I would like to run stand-alone QM/MM calculations for a large zeolite model containing various metal complexes in the pore space.
I have a few questions,
I am having to define atom types, charges and LJ parameters for my system. If I define only these three parameters, does QChem use the forcefield defined in the $rem section to fill in the other parameters such as bond, and torsion parameters?
What are some tips to speed up the QM/MM calculation?
No, Q-Chem is unable to automatically fill in missing parameters. When using custom forcefield definitions, all the forcefield parameters must be defined in $force_field_params as described in 11.3.3 Using the Stand-Alone QM/MM Features⣠11.3 Stand-Alone QM/MM Calculations ⣠Chapter 11 Molecules in Complex Environments: Solvent Models, QM/MM and QM/EFP Features, Density Embedding ⣠Q-Chem 5.4 Userâs Manual
Q-Chem provides a zeolite field as defined in Improved Force-Field Parameters for QM/MM Simulations of the Energies of Adsorption for Molecules in Zeolites and a Free Rotor Correction to the Rigid Rotor Harmonic Oscillator Model for Adsorption Enthalpies | The Journal of Physical Chemistry C (acs.org). For demonstration, please refer to a sample job shipped with Q-Chem named QMMM_ZEO-force.in.
The answer to this question depends on the details of a specific calculation as computational bottlenecks may vary. General suggestions include appropriate choices of QM method, basis, parallelism. If you post an input example here or send it to support@q-chem.com, we will be able to give better advise.
Thank you for your reply. I have sent an email to the support