[CP2K:6441] Problems with GAPW + external potential

[Juha Ritala]

Hi Matt,

thank you for the patch. I think this approach makes sense. If I understood 
correctly, *rho0_s_rs* is the realspace grid representation of the charge 
density *ñ^0* (in the GAPW paper from 1999), and *ñ^0 *is sort of a 
representation of the charge density in the atomic region using the set of 
soft Gaussians. At least the multipole moments of the atomic charge density 
and *ñ^0 *are equal, so in a sufficiently large length scale these charge 
densities are approximately the same. This would imply that for moderate 
electric fields this approximation would indeed be fine.

I will check how this patch works for me and keep you informed.

- Juha

On Saturday, 16 May 2015 13:03:25 UTC+3, Matt W wrote:
>
> Hi Juha,
>
> there are a couple of files attached (compatible with latest version of 
> cp2k at time of writing, but there are only a couple of lines changed) you 
> can try and see if it works with GAPW. It only works with the soft part of 
> the density, including the compensation charges. As the compensation 
> charges, including the core, are put onto the fft grid the core routines in 
> external_potential need to be protected. Might need tidying for mixed 
> gpw/gapw.
>
> I guess this approximately means that the core (i.e. any functions on the 
> hard atomic grids) isn't directly polarized by the field? For modest fields 
> it should be fine, maybe?
>
> Let me know how it goes,
>
> Matt
>
>
> On Friday, May 1, 2015 at 3:46:30 PM UTC+1, jgh wrote:
>>
>> Hi 
>>
>> unfortunately, I don't have time to look into this. 
>> It seems to me that for analytic potentials it wouldn't be that hard, 
>> but for potentials read in on a grid it would need special care. 
>>
>> regards 
>>
>> Juerg 
>> -------------------------------------------------------------- 
>> Juerg Hutter                         Phone : ++41 44 635 4491 
>> Institut für Chemie C                FAX   : ++41 44 635 6838 
>> Universität Zürich                   E-mail: hut... at chem.uzh.ch 
>> Winterthurerstrasse 190 
>> CH-8057 Zürich, Switzerland 
>> --------------------------------------------------------------- 
>>
>> -----cp... at googlegroups.com wrote: -----To: cp... at googlegroups.com 
>> From: Juha Ritala 
>> Sent by: cp... at googlegroups.com 
>> Date: 04/30/2015 01:18PM 
>> Subject: Re: [CP2K:6441] Problems with GAPW + external potential 
>>
>> Hi Juerg, 
>>
>> thank you for confirming this. Is there any chance that this will be 
>> fixed in the near future, or should I stick with GPW for the time being? I 
>> could try and fix it myself, but as far as I understand how GAPW works, 
>> considering the contribution from the local atomic charges is not at all 
>> trivial. 
>>
>> - Juha 
>>
>> On Wednesday, April 29, 2015 at 2:17:45 PM UTC+3, jgh wrote:Hi 
>>
>>
>>
>> yes, this is a bug. The external potential is applied to the 
>>
>> charge on the plane wave grid. In GAPW only the soft part 
>>
>> of the charge is on the grid and one would have to also compute 
>>
>> the contributions from the local atomic charges. 
>>
>>
>>
>> regards 
>>
>>
>>
>> Juerg Hutter 
>>
>> -------------------------------------------------------------- 
>>
>> Juerg Hutter                         Phone : ++41 44 635 4491 
>>
>> Institut für Chemie C                FAX   : ++41 44 635 6838 
>>
>> Universität Zürich                   E-mail: hut... at chem.uzh.ch 
>>
>> Winterthurerstrasse 190 
>>
>> CH-8057 Zürich, Switzerland 
>>
>> --------------------------------------------------------------- 
>>
>>
>>
>> -----cp... at googlegroups.com wrote: -----To: cp... at googlegroups.com 
>>
>> From: Juha Ritala 
>>
>> Sent by: cp... at googlegroups.com 
>>
>> Date: 04/29/2015 09:52AM 
>>
>> Subject: [CP2K:6432] Problems with GAPW + external potential 
>>
>>
>>
>> I have had some problems when I tried to use GAPW method combined with an 
>> external potential. To demonstrate what seems to be the source of the 
>> problems, I made this simple test case with a water molecule in a constant 
>> external potential. Physically, the constant background potential should 
>> not affect the total energy of the water molecule since the molecule is 
>> charge neutral. The energy does change as a function of the constant 
>> potential when the GAPW method is used, however. You can see this in the 
>> attached energy vs. background potential plot. GPW method gives expected 
>> behaviour, the total energy stays perfectly constant when the potential is 
>> varied. 
>>
>>
>>
>> It seems as if some part of the charge in the system is unaffected by the 
>> external potential in GAPW and thus the total charge is effectively 
>> non-zero. Is this a bug or is there some part of the implementation 
>> missing? 
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>>
>>
>> [attachment "E_vs_V_GAPW_and_GPW.pdf" removed by Jürg Hutter/at/UZH] 
>>
>> [attachment "H2O_constant_extpot_GPW.inp" removed by Jürg Hutter/at/UZH] 
>>
>> [attachment "H2O_constant_extpot_GPW.out" removed by Jürg Hutter/at/UZH] 
>>
>> [attachment "H2O_constant_extpot_GAPW.inp" removed by Jürg Hutter/at/UZH] 
>>
>> [attachment "H2O_constant_extpot_GAPW.out" removed by Jürg Hutter/at/UZH] 
>>
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