[Pw_forum] negative charge density!

[Paolo Giannozzi]

On Tuesday 12 July 2005 20:28, Mousumi Upadhyay Kahaly wrote:

> How come I get such negative values (mainly around the Cd atom,
> as found) which is not negligible? What is the meaning of this
> NEGATIVE charge density? Can anyone please tell me, what is the
> mistake that I have made what should I do to get rid of this?

there is no mistake. Ultrasoft pseudopotentials may give raise to 
a small negative charge, for various reasons that are explained in 
the manual. In most but not all cases, it disappears with increasing 
cutoff (see for instance:
http://www.democritos.it/pipermail/pw_forum/2003-April/000207.html ).

In your case the pseudopotential of Cd is clearly the culprit. I am a 
little bit puzzled by the size of the negative charge, which does not 
seem to be reduced by increasing cutoff, so please check carefully 
in simple systems the correct behavior of the Cd pseudopotentials.

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