[CP2K:4443] QMMM Periodic

Teodoro Laino teodor... at gmail.com
Tue May 28 05:42:25 UTC 2013


these questions were discussed few times in the past. Nonetheless, as a recap:

On May 26, 2013, at 12:27 PM, mark <ridd... at gmail.com> wrote:

> Dear CP2K developers,
> I have some doubts about my QMMM calculations (I'm simulating one quantum glucose molecule 
> in a classical Ionic liquid + water solvent).
> I set &PERODIC = NONE for QM CELL, in &QMMM (and I set no PBC in DFT section for the POISSON solver), &PERIODIC = XYZ in &SUBSYS and I set
> ECOUPL=GAUSS for the QM/MM interaction.
> I have several question about the PBC:
> 1- with this setting I'm decoupling the QM CELL from all the other periodic QM images (because I set &PERODIC = NONE for QM CELL ), keeping only the zero-cell electrostatic between QM and MM + 
> the interaction between QM and MM repeated images up to the cutoff (because I set &PERIODIC = XYZ in &SUBSYS )?

> 2- with this setting MM atoms interact only with the thier images or also with the QM images (because I set &PERIODIC = XYZ in &SUBSYS )?
only with their MM images and with the zero-image QM atoms

> 3- if I set &PERODIC = NONE for QM CELL and PERIODIC = XYZ  in DFT section for the POISSON solver, would it has sense?

> 4- if QM CELL hasn't PBC (as in this case) there is the possibility that the QM atoms go away from the QM box?
There is the possibility that QM atoms leave the QM box even if you have periodicity. The QM box is something localised in space and this has nothing to do with the keyword PERIODIC in &CELL. This is controlling only the construction of a part of the KS Hamiltonian.
In both cases (PERIODIC or NON-PERIODIC) if your atoms leave the QM box you are in trouble (unless the QM box is equal to the MM box - indeed there are cases where one may want to have such  a setup).

If your molecules are particularly mobile, or you plan to explore nanoseconds of MD simulations, you should think to use the adaptive QMMM for "solving" the issue of transforming QM <-> MM .. It's basically there.. few people are using it, you can give it a try.. of course at your own risk (and your own learning).


> Can someone clarify this to me?
> Thank you very much 
> Kind Regards
> Marco
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