[Wien] Weird wannier functions coming out from wien2wannier

[Elias Assmann]

Pablo,

On 02/15/2016 05:17 PM, Pablo Villar Arribi wrote:
> Any ideas on why this different behaviour between Wien2k and Quantum
> Espresso? Could it be due to the intrinsic diferences between an
> all-electron code and a pseudopotential code in terms of their Bloch
> states, which are used as a starting point for Wannier90?

I think it is much more likely to be a problem in wplot [unfortunately
for me :-)].  In particular, it sounds like you have a good projections,
but something is going wrong in the plotting itself.

Here are some suggestions:

1. By way of general advice, I suggest to start with a coarse r-mesh
(e.g. 10×10×10 points) and a larger plot region than you think you need,
to figure out the correct plotting window.  You said you checked this,
but it can really be tricky, what with different settings both in
Wannier90 (translate_home_cell) and wplot2xsf (-noshift).  Once you have
that, you can scale up the precision.

2. All parts of the calculation (mainly, case.chk and case.vector) have
to match.  If, for some reason, you ran another lapw1 after wannier90,
wplot will not work.  Therefore, it sometimes helps simply to repeat the
whole procedure (lapw1 && w2w && wannier90 && wplot), just to be sure
that there is no inconsistency.

3. Did you check if the real-space representation of the WF is real
(i.e., case.psink should be 0 or ±π up to numerical precision)?  Because
the xsf format does not accomodate complex numbers, wplot2xsf by default
writes |w(r)|² sgn Re w(r).  This could lead to “strange” isosurfaces if
there is a phase.

4. If the above does not help and you just want your plots, it could be
an option to simply use the ones from Quantum Espresso.  In my view,
real-space WFs are a qualitative rather than a quantitative tool (unless
you are very careful …), therefore it could be okay to use the QE
real-space WFs as a visualization for your Wien2k WFs, as long as H(R)
and the band structure are “the same”.  Obviously, this depends on what
you want to do with them.

5. On the other hand, if you want to get it right with Wien2k (and
possibly help me find a bug), the next thing I would try is a different
version of wplot (I am assuming that you tried the one included in
Wien2k 14.2).  This is one part of the package that I changed quite a
lot recently and invariably, bugs creep in.  You could either try the
newest version from GitHub (caveat: the format of case.inwplot changed)
where some of those bugs are fixed; or the  “old” one (0.97, available
at
http://www.ifp.tuwien.ac.at/forschung/arbeitsgruppen/cms/software-download/wien2wannier/),
which has a different set of bugs.

6. Relatedly, what crystal structure do you have?  Wien2Wannier has had
some problems with more “difficult” lattice types in the past.


Good luck,

	Elias

-- 
Elias Assmann

Wien2Wannier: maximally localized Wannier functions
              from linearized augmented plane waves

                     http://wien2wannier.github.io/
      https://github.com/wien2wannier/wien2wannier/

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