energy conservation during a QMMM run

[Csilla Varnai]

Thanks very much for the hints. I'm really sorry for having to write  
again, but possibly because of my lack of experience with CP2K and  
QMMM calculations, I didn't entirely understand what I should do. I've  
been trying to play around with the test files, and find out what  
exactly I need for an energy conserving QMMM calculation. I'm trying  
to run a cell of 3 water molecules.
Should I both set the QM cell to the same size as the MM cell and  
decouple the QM periodic images? Is that right what I'm trying to do?  
And I don't even really know if I should use anywhere anything else  
than the default.
I tried to run this input file but it gave me Segfault. I'd be  
grateful if anyone could help me with what's wrong.
Regards,

Csilla
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On 16 Apr 2008, at 14:24, Teodoro Laino wrote:

>
>> &FORCE_EVAL
>>  METHOD QMMM
>
> First of all in the DFT section there is not decoupling section.. in
> this case your QM periodic images will be coupled with the
> same periodicity of the QMMM cell. To be really consistent you may
> want in this case have EXACTLY the same cell between MM and QM.
>
>>
> Second.. your QMMM calculation does not specify any periodicity for
> the QMMM coupling. This means that the electrostatic coupling is
> evaluated
> always according the PBC between QM and MM atoms. If an atoms is
> going out of the cell and is wrapped back in the cell (due to the
> PBC) than OF COURSE your system cannot conserve the total energy.
> If you want a fully energy conserving QMMM-MD you've to specify that
> you want a QMMM periodic coupling (treating the electrostatic through
> an Ewald sum): have a look at the few templates in the tests
> directory (of course the number have been properly adapted, those are
> silly).
>
>>
>
> Teo
>
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