[Pw_forum] Warning message - negative or imaginary core charge

Paolo Giannozzi giannozz at nest.sns.it
Thu Jul 1 16:27:53 CEST 2004

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?


> Or  is the value of -0.000003 small enough to ignore?


> 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 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

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