[Pw_forum] question about the core charge

[Stefano Baroni]

Hi Sun:

here attached I join a copy of one of the many answers already given to 
your question which has been asked many times already. We know that the 
manual is (still ;-) far from being perfect, but I recommend that, 
before, you post questions like this, you make a search in the archive 
of the pw users' mailing list (righ-bottom button in the Pwscf.org home 
page). The Message attached was found in less than 10 secs!

Thank you for your interest and support.

Yours - SB

On Nov 29, 2004, at 10:06 AM, Shaorui Sun wrote:

> Dear all:
>     when I use the pwscf to calculate the HgS crystal,there is a 
> warning occurring before the 1st iteration as follows:
>    warning: negative or imaginary core charge    -0.000077    0.000000
>    who can tell me what is the matter, and how can I solve it?
>
> Best Regards!
>                         S. R. Sun
> ---------------------------------------------
> Beijing Synchrotron Radiation Facility
> Institute of High Energy Physics
> Chinese Academy of Sciences
> P. O. Box 918, 100049 Beijing
> P. R. China
> Tel: 0086+10 88236710
> email:sunsr at ihep.ac.cn
>
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>



[Pw_forum] Warning message - negative or imaginary core charge
  Paolo Giannozzi   pw_forum at pwscf.org
  Thu, 1 Jul 2004 16:27:53 +0200

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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
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