[CP2K:3795] Poisson solvers in QMMM

[Frank Uhlig]

Dear Teodoro,

thanks for taking your time to help. I have one more question left
concerning the QMMM input. The keyword %FORCE_EVAL%QMMM%CELL%PERIODIC
does not seem have any influence at all on the calculation. Did I miss
something here?

Best,

Frank

On Fri, Apr 20, 2012 at 7:21 PM, Laino Teodoro <teodor... at gmail.com> wrote:
> Dear Frank,
>
> On 20 Apr 2012, at 18:48, Frank Uhlig <uhlig... at googlemail.com> wrote:
>
> Dear Teodoro,
>
> thanks for the answer. It is not true that "nothing prevents [me] from
> implementing" the recoupling for different Poisson solvers. As you may
> understand, there are certain constraints given by work and personal
> obligations.
>
>
> Absolutely understandable. Similarly, I think is understandable that, for
> personal and work constraints, not all have the time to read (and possibly
> show interest for) such long messages.
>
> If _you_ decide to do it all in your free time that is your choice and also
> highly appreciated. But please, remember that it takes time to get familiar
> with the code, cp2k is a rather large project and not all of us are familiar
> with FORTRAN, good programmers and might have to use cp2k as a black box.
>
> Just lines that nothing add to the real problem communication..
>
> This brings me to issue on hand, as a "cp2k-black-box-user" I noticed
> several inconsitencies in what is written in the reference manual and what
> is happening during the calculation:
>
> The section %FORCE_EVAL%QMMM%PERIODIC is classified as "cannot be optional"
> in the manual. If you take the test from the before mentioned post, you can
> easily check that this section behaves differently and also results will
> differ depending on its presence in the input file.
>
> Cannot be optional, means: there is no default associated to it: if you want
> qm/mm periodic you need to specify it.
> No periodic: isolated QMMM
> Any PS can be used in that case..
>
> The section %FORCE_EVAL%QMMM%PERIODIC %MULTIPOLE is classified as "can be
> optional" and the explanation of its purpose is:
>
>
> See above... It is on by default if you have PERIODIC (with default values)
>
> "This section is used to set up the decoupling of QM periodic images with
> the use of density derived atomic point charges."
>
> Whether this section is included or not does not change the resulting total
> energy and in both cases the output states "Recoupling energy [...]".
>
> See above.
>
> Those two things, seem to be either bugs or errors in the input description.
> I would appreciate if you could comment on what is what.
>
>
> See above.
>
> Furthermore, the Wavelet solver can in principle be employed without further
> implementations.
>
>
> Please do it. For me is not trivial at all to handle in a larger box the
> recoupling with WAVELET (given a smaller QM box) (which in 2006 was not even
> there, btw)
>
> When one sets the corresponding periodicity in the DFT settings to XYZ the
> calculation will be equivalent to a plain, periodic plane-wave calculation
> and the de- and re-coupling can be used for that and is fully equivalent to
> using the Multipole solver (also really gives fully equivalent results).
>
>
> Again, if you know how to do it... Do it.
>
> CP2k in some places gives error messages for "illegal combination[s]" of
> keywords and in my opinion it would be helpful to get such an error message
> for the combination of the Wavelet solver (for isolated system) and what
> seems to enable recoupling in the input. Btw, as far as I know,
>
> thanks for the suggestion: according my personal and work constraint, I may
> decide to implement that
>
> your 2006 JCTC publications about the QMMM boundary conditions does not
> mention that the recoupling is not possible for other Poisson solvers and
> the behaviour of CP2k with respect to the input is just a bit deceiving.
>
> Sure... But strange enough in my 2006 JCTC I only discuss about the DDAPC
> scheme.. Maybe there is a reason (deeply hidden) for that?
>
> Thanks in advance and best regards,
>
>
> You're welcome.
> Teo
>
> Frank
>
> On Apr 20, 2012 5:23 PM, "Teodoro Laino" <teodor... at gmail.com> wrote:
>>
>> Dear Frank,
>>
>> you have already found the reasons. In order to have recoupling the only
>> poisson solver working at the moment is multipole.
>> Nothing prevents you from implementing also for the other solvers
>> something similar.
>> If instead you want to use cp2k as a black box, you have to stay within
>> the implementation borders (see papers and regtests input provided):
>> everything beyond that is not guaranteed to work.
>> Regards,
>> Teo
>>
>> On Apr 20, 2012, at 4:56 PM, Frank Uhlig wrote:
>>
>>> Dear CP2k'lers,
>>>
>>> related to a previous post
>>> (https://groups.google.com/d/topic/cp2k/iMsqLpZnRyQ/discussion) I just
>>> wanted to highlight the main problems again, because they might have been
>>> hidden in the mess.
>>>
>>> The QMMM electrostatic coupling is different for different Poisson
>>> solvers if analogous inputs with Wavelet and Multipole solver are used. In
>>> the example from the previous post (using Multipole solver) the QM images
>>> are recoupled. If one just changes the Poisson solver to the Wavelet solver,
>>> no recoupling of the QM images is performed. This behaviour then further
>>> depends on the inclusion/exclusion of the non-optional section
>>> %FORCE_EVAL%QMMM%PERIODIC.
>>> The input can be changed in a way that one reproduces the total energies
>>> with both Poisson solvers (up to ~0.01 eV).
>>>
>>> This behaviour is counterintuitive, imo, and I would appreciate comments
>>> of the developers, if it is intended, if I am doing something wrong etc pp
>>>
>>> Cheers,
>>>
>>> Frank
>>>
>>>
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