[Pw_forum] About background charge

[Lorenzo Paulatto]

On Tue, July 7, 2009 08:27, oulihui666 wrote:
>  Thus, I'd like to ask if PWSCF can do calculations that vacuum layer do
>  not fill backgrount charges ?

The system is not really filled with background charges, what is really
done is actively set the G=0 component of V to zero. In this way the
average value of the potential over the unit cell is zero, and everything
works fine (if you can afford a cell big enough to suppress periodic image
interaction)

>  I have checked the manual and original pipemails, but didn't find many
>  topics on background charges.

There are a few, e.g.
<http://www.democritos.it/pipermail/pw_forum/2005-April/002379.html>

>  However,I found many discussions on EXTERNAL POTENTIAL which makes it
>  possible to add an external electrostatic field.
>  If possible, how ?

Have a look at the documentation, Doc/INPUT_PW.html; there are two ways to
do it: using a sawtootk potential or using the modern theory of
polarization (Berry phase); the latter is only implemented for insulators.

>
>  Many thanks.

best regards



-- 
Lorenzo Paulatto
SISSA  &  DEMOCRITOS (Trieste)
phone: +39 040 3787 511
skype: paulatz
www:   http://people.sissa.it/~paulatto/



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