[Pw_forum] About postprocessing
baroni at sissa.it
Tue Nov 21 05:14:01 CET 2006
On Nov 21, 2006, at 12:26 AM, Giuseppe Piero Brandino wrote:
> Dear espresso user,
> i have some questions about the pp.x program.
> Asking the code to write the potential, for example
> plot_num=11=the V_bare + V_H potential,
> does it print the potential or the potential energy?
> I know that it prints it in Rydberg, so an energy.
> How do i get the potential? simply dividing by e
> or dividing by the total (ionic and electronic) charge density
> in each point?
this is a bit confusing to me. why would you divide by the local
charge density? an energy divided by a charge density makes a
potential times a volume, which is not what you expect, and
furthermore I am not aware of any sensible use of the resulting
> Something else,
> is there a simple way to get the total charge density (electronic +
> ionic) from pp.x?
The ionic *pseudo*charge density is ill-defined when the
pseudopotential is non local (as it usually the case). On the other
hand, the physical (all-electron) valence+core charge density is not
simply the sum of the valence pseudo-charge+ionic charge. What would
be needed here is the sum of the all-electron ionic charge density +
the valence charge density obtained from the reconstructed wave-
functions. This is what is done the PAW formalism (see PE Bloechl,
Phys. Rev. B 50, 17953 - 17979 (1994)). Work is in progress to
implement PAW in Quantum Espresso. Meanwhile, there might be tools
available to obtain a (more or less) quick-and-dirty recostruction of
the charge, but others may be more appropriate than me to address
Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center -
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
Please, if possible, don't send me MS Word or PowerPoint attachments
Why? See: http://www.gnu.org/philosophy/no-word-attachments.html
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