[CP2K:2704] Reference point for molecular dipoles

Ondrej Marsalek ondrej.... at gmail.com
Tue May 11 09:55:21 CEST 2010


Thank you very much for the explanation. I must say that "atomic
charges" sounded like some population analysis is involved. From your
description, I gather it really means "charges of the cores". If this
is really the case, it now makes good sense to me and the options are
just fine.

Regards,
Ondrej


On Tue, May 11, 2010 at 08:55, Juerg Hutter <hut... at pci.uzh.ch> wrote:
> Hi
>
> the total dipole is given as the sum of electronic and nuclear
> contributions. Both contributions depend on the center of
> origin and for neutral molecules this dependence cancels.
> For ions this is not the case and you geta dependence on the
> reference point. COAC (center of atomic charges) was chosen
> as the reference point as it fully cancels the contribution
> from the ions and leaves only the electronic contribution.
> In other words, it minimizes the size of the electronic part
> of the dipole.
> Your suggestion would achieve the same but with the nuclear
> contribution, the electronic contribution would be zero and
> the nuclear minimal.
> I prefere the COAC reference point as it only depends on
> the molecular coordinates (and ionic charges). If you calculate
> the same molecule with a different electronic structure method
> you will have the same reference point and you can compare
> the results.
>
> regards
>
> Juerg
>
> ----------------------------------------------------------
> Juerg Hutter                   Phone : ++41 44 635 4491
> Physical Chemistry Institute   FAX   : ++41 44 635 6838
> University of Zurich           E-mail: hut... at pci.uzh.ch
> Winterthurerstrasse 190
> CH-8057 Zurich, Switzerland
> ----------------------------------------------------------
>
>
> On Mon, 10 May 2010, Ondrej Marsalek wrote:
>
>> Dear all,
>>
>> I am looking at the key:
>>
>> CP2K_INPUT / FORCE_EVAL / DFT / PRINT / LOCALIZATION /
>> MOLECULAR_DIPOLES / REFERENCE
>>
>> and one of the possible values is "COAC", with the description "Use
>> Center of Atomic Charges". I would like to ask how are these atomic
>> charges calculated. It would be nice to have the option to simply use
>> the center of charge assigned to that molecule based on the Wannier
>> centers, but that seems to be missing, as far as I can tell. I want to
>> get the molecular dipole of an ion, so the default value "ZERO" is no
>> good and center of charge seems a better choice than center of mass.
>>
>> Thanks,
>> Ondrej
>>
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