[CP2K:9616] PM6 Mulliken charges

Stanislav Šimko stanisl... at gmail.com
Mon Nov 6 19:09:20 CET 2017


Hi,

yes, thank you for your reply. Appropriately modifying the Coulomb cutoff 
is what we found out as well. And it makes sense, because electrostatic 
interactions are computed with classical Coulomb formula with cutoff. Since 
we had default large cutoff, (much larger than c/2, c is box size), 
particles would see several images of others, introducing artifacts into 
the calculation.

Thank you.
best,
stanislav.

On Monday, November 6, 2017 at 6:24:15 PM UTC+1, jgh wrote:
>
> Hi 
>
> SE periodic calculations are non trivial, as there are many options 
> and no fully tested default values. 
> I have done a calculation as described in your mail and I get 
> consistent results for the Mulliken charges of approx. 
> O -0.610 
> H  0.305 
>
> My input is attached. 
>
> 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 
> <javascript:> 
> Winterthurerstrasse 190 
> CH-8057 Zürich, Switzerland 
> --------------------------------------------------------------- 
>
> -----cp... at googlegroups.com <javascript:> wrote: ----- 
> To: cp2k <cp... at googlegroups.com <javascript:>> 
> From: Stanislav Šimko 
> Sent by: cp... at googlegroups.com <javascript:> 
> Date: 11/02/2017 09:47AM 
> Subject: [CP2K:9616] PM6 Mulliken charges 
>
> Dear Cp2k users, 
> I've wanted to do some calculations using periodic PM6 and calculate 
> Mulliken charges, however, I got some weird results. I compared atomic 
> charges of two systems - in the first one I've got a single water molecule 
> in a periodic box (~14A box), and in the other one the same situation is 
> triplicated in all three directions (still periodic, ~42A). So the geometry 
> of the system is the same in both cases, but the computed atomic charges 
> are not the same: 
>
>       h2o              triple h2o 
> Ox        6.184751      6.697106 
> Hy        0.905911      0.642258 
>  Hy        0.909339      0.660701 
>
> Can anyone clarify why is this happening? I would expect that I obtain the 
> same results. 
> Thank you for the help! 
>
> Stanislav 
>   
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