[Pw_forum] Negative charge !

[Nicola Marzari]

Dear Von,


I'm not sure on how the augmented charge is represented in PWSCF,
but in CP a multipole expansion is made - this in principle can
give rise to negative charge densities. The values posted also
seemed very small, so I'd say nothing to worry.

Note also that "cold-smearing" has the same advantages of 
"methfessel-paxton", but does not introduce negative charge
densities. However, it's unlikely that smearing is the issue.

				nicola



Von Braun Nascimento wrote:
> Dear all,  
> 
> I am trying to generate some charge plots for a prototype bulk La/Sr
> manganite. 
> The 1-D charge plot along Sr-O atoms is negative close to the Sr core,
> although it does not happen along La-O atoms. I've checked PW forum archives
> and there is a comment about increasing the number of k points or the
> cut-off energy.  I've increased both (see attached input files) and nothing
> has changed so far. Why do this negative charge problem is present only
> close to Sr ? 
> Thanks in advance. 
> 
> Regards, Von  


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Prof Nicola Marzari   Department of Materials Science and Engineering
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