[Pw_forum] (no subject)

[Stefano Baroni]

Dear Kai: this issue has been discussed many times on this mailing list.
The best way of using the mailing list is to search first the archive. 
Just go to the PWscf.org web site, and click the "search archive" 
button on the bottom right corner of the page. If you search the 
archive with "negative as keyword" you would find a number of threads 
that might interest you. In the specific case, with very little effort 
I found the following:
>
> On Thursday 01 July 2004 05:37, Aloysius Soon Sze Lok wrote:
>
> >   warning: negative or imaginary core charge    -0.000003    0.000000
> > [...] Is this a serious warning?
>
> no
>
> > Or  is the value of -0.000003 small enough to ignore?
>
> definitely
>
> > May I know the implications, please?
>
> in this particular case, none. In general: if you transform a positive
> function in real space to Fourier space and truncate at some finite
> cutoff, your positive function is no longer guaranteed to be positive
> when you transform back to real space. This happens only with
> core corrections and with ultrasoft pseudopotentials. It can be a
> a source of trouble, but it is usually solved by increasing the cutoff
> for the charge density
>
> Paolo
>
> -- 
> Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
> Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513
> Piazza dei Cavalieri 7      I-56126 Pisa, Italy

Hope this helps and clarify both the specific case and the general 
issue of an efficient usage of this mailing list.

Best wishes,
Stefano

PS: we probably ought to modify this warning in such a way to make it 
more informative, or else suppress it ... ;-)


On Jan 14, 2005, at 11:03 AM, Kai-Felix Braun wrote:

> Hi,
> I a doing an scf run with Au,C,S and H atoms and am using the PBE
> pseudopotentials from the pwscf web page. I am getting
>
>   warning: negative or imaginary core charge    -0.000003    0.000000
>
>      Initial potential from superposition of free atoms
>
>   Warning: negative or imaginary starting charge    -0.000128    
> 0.000000  1
>
>      starting charge =1596.46596
>
> What needs to be done in this case ? Is this related to the 
> pseudopotentials
> ?
> Regards
> Kai Braun
>
> -- 
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---
Stefano Baroni    ---  SISSA  &  DEMOCRITOS National Simulation Center
via Beirut 2-4 34014 Trieste Grignano / 
[+39] 040 3787 406 (tel) -528 
(fax)

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