[CP2K:2577] Re: QM/MM with isolated QM box

Laino Teodoro teodor... at gmail.com
Sat Feb 20 17:23:00 UTC 2010

Dear Shihao,

It is a bug in the input, a quite severe one.
I would highly recommend you to stop QM/MM for a while and check/ 
study more carefully how Quickstep and in general plane wave codes  
work, with a focus on all problems related to them. Otherwise the  
risk is that the amount of numbers that you produce are just trash.

Anyway: you use MT decoupler (check MT references about problems VS  
cell size)+2water molecules+a box of 6x6x6 angstrom.

There is a quite big inconsistency: size of the cell VS you QM system  
VS MT decoupling.
After moving your cell to a more reasonable value the 2 waters  
molecule move like they would normally do.

If you keep them tightly frozen in a small box you can't expect see  
them moving.


On 20 Feb 2010, at 17:01, shihao wrote:

> Hi there,
> I reproduced the error with a smaller system (2 QM water and 21 MM
> water).  When I tried to further reduce the system and use only 1 QM
> water, the simulation worked fine and the QM water travelled freely.
> I've uploaded all the needed files (in qmmm_water_shihao_tar_gz.zip).
> If you run the simulation, you will see that the QM water molecules
> (resid 1 and 2) more or less stay in the YZ plane (which means that
> they could not rotate freely in all directions) after about 200 steps.
> I've also included some result files (dcd, cube, etc.) for your
> convenience.
> Could you give me some clues on whether this is because of some errors
> in my input file or some bugs in the code?
> Many thanks!
> Regards,
> Shihao
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