[Pw_forum] VCA calculations with PWscf for partially occupied sites

[Kiss, Ioan]

Dear PWscf community,

I am wondering whether one can perform calculations with PWscf
using the virtual crystal approximation (VCA) for systems, where one
site is only partially (10-30%) occupied by a magnetic atom, and the rest of
the site is empty?

I am interested in using VCA in combination with LDA+U or PBE+U, because
I have to study a large system which does not work with full-electron codes
where one can take advantage of the coherent potential approximation (CPA).

By browsing through the mailing list, as I understood, in PWscf
such VCA calculations can be performed by generating first a new "mixed" type
pseudopotential with the virtual.x utility. I can imagine how that would work,
if I have a system where as an example one has a mixture of 50% Fe
and 50% Co or something similar on an atomic site.
However, how is one supposed to proceed, if a site is only partially occupied,
and the rest of the site is empty?
Can one even generate such thing as a completely empty potential, which than
need to be mixed with the real potential of the particular atoms (Fe and Co in my case)?
If yes, would that still work with VCA, and would the results be trustworthy?


Any helpful remark/comment is appreciated.

Best regards,
Janos.


==========================================
  Dr. Janos Kiss      e-mail: kissi at uni-mainz.de
  Johannes Gutenberg-Universitaet
  Institut f. Anorg. u. Analyt. Chemie
  AK Prof. Dr. Claudia Felser
  Staudinger Weg 9 / Raum 01-230
  55128 Mainz/ Germany
  Phone: +49-(0)6131-39-22703
  Fax:     +49-(0)6131-39-26267
  Web:     http://www.superconductivity.de/
 =========================================
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