[Wannier] Recreating radial wavefunctions from pw2wannier90 or wannier90 outputs

[Erica Kotta]

Hello Stepan and Giovanni,

Thank you so much for your responses and advice! The links were very useful
for learning how to get the UNK files open, and indeed I found pre-written
code online for opening and plotting the xsf files in MATLAB, which I have
used to get a closer look at the Wannier functions.

However, reflecting on these answers for the past couple of days, I have
realized I was missing a very fundamental part of the picture of the
Wannierization process. A bit embarrassing to say and I don't know how I
missed this through all of the examples I've gone through already, but I
thought that the Wannier functions would also replicate the
higher-level-ness of the underlying orbitals. The plots in xcrysden I've
come across only show the lowest-level orbitals for each l-value (for
example only 2p orbital character, even when you know that the bands of
interest are 3p or 4p). I thought that by getting the underlying xsf
numerical data or recreating the plots from the Umn/UNK files, I would be
able to resolve the "missing" nodes.

I never ran any examples or previous projects with any r-value other than
the default. It is a little interesting (concerning?) to me that
disregarding the correct number of nodes in the radial function can still
preserve most of the important physics, etc. Unless, of course, I am still
missing something. (But, I'm assuming that setting a higher r-value in the
projections section of the Wannier input wouldn't necessarily correspond to
the proper n-valued, l>0 radial wavefunction...)

I think that the pp.x function from the Quantum Espresso end might get me
closer to finding the radial wavefunction I'm looking for, which is what
I've been working on now.

Best,
Erica Kotta
Physics PhD student at New York University








On Thu, Oct 29, 2020 at 2:04 PM Giovanni Pizzi <giovanni.pizzi at epfl.ch>
wrote:

> Dear Erica,
> I am not sure if I'm misunderstanding your question, anyway here are some
> answers based on what I think you might need:
>
> - the initial projections are generated by the interface code (e.g.
> pw2wannier90) so you should try to have them printed there. Anyway, their
> analytical form is tabulated in the user guide so you should be able to
> create their numerical representation on a grid yourself.
>
> - Those, anyway, are just the starting point of the Wannierisation. The
> code computes the WFs and then uses the minimised U matrices (unitary
> transforms), and the UNK files from the ab-initio code (periodic part of
> the Kohn-Sham wavefunctions) to plot the final WFs in real space (there is
> a flag in the input to have W90 print the xsf files, or also in cube
> format). The flags, and the detailed specification of the format of the
> various files, is explained in detail in the Wannier90 user guide.
>
> - if what you want is just the numerical data in the XSF (so, the Wannier
> functions in real space), you can just open and parse the XSF file, the
> numbers are in there (the XSF format is well documented, just google for
> 'xsf specification'). There might even be codes around that already parse
> it, probably.
>
> Best,
> Giovanni
>
> P.S.: remember to sign your emails with your affiliation
>
> --
> Giovanni Pizzi
> Theory and Simulation of Materials and MARVEL, EPFL
> http://people.epfl.ch/giovanni.pizzi
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__people.epfl.ch_giovanni.pizzi&d=DwMFAg&c=slrrB7dE8n7gBJbeO0g-IQ&r=7kPw3aoa7AkFV5gOHDjkjg&m=q0rWU01TyaYCYNqTOeJhDRTo6X7NS4WlZ559fKI7GIs&s=XtLucDjScMUdTf4qXrPZggFWxf7eD_c3El7Mjh6Qtyg&e=>
> http://nccr-marvel.ch/en/people/profile/giovanni-pizzi
>
> On 28 Oct 2020, at 19:40, Erica Kotta <eck325 at nyu.edu> wrote:
>
> Hello,
>
> I have a Wannier90 output where I have projected a group of isolated bands
> onto a set of p- and d-orbitals.
>
> Is it possible to see the radial wave functions used by the Wannier90
> software? I see in the User Guide tables 3.1-3.3 they list the angular
> functions and then a possible choice of radial functions, but is there a
> way to see the actual form that was used, that represents the actual basis?
> Does it entail outputting the Umn matrices, and using the UNK...NC to
> recreate them as in Equations 1&2 in Wu's paper (
> https://www.labxing.com/files/lab_data/496-1580695056-bV5W1jk8.pdf
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__www.labxing.com_files_lab-5Fdata_496-2D1580695056-2DbV5W1jk8.pdf&d=DwMFAg&c=slrrB7dE8n7gBJbeO0g-IQ&r=7kPw3aoa7AkFV5gOHDjkjg&m=q0rWU01TyaYCYNqTOeJhDRTo6X7NS4WlZ559fKI7GIs&s=bdK40YTPqqy6LNK834rpl2Oshc2HLX4F-orE81kqw2o&e=>)?
>
> (And if this is the case, how do you open/read these UNK...NC files?)
>
> Basically, I was wondering if I could get some set of numerical data
> representing what we see when we plot the xsf files in xcrysden.
>
> Thank you very much in advance,
> Erica
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