[QE-users] Unfold.x colormap (6.6)

[William Hewett]

Hi Pietro,

Thanks for your detailed answer, also for the unfold.x code and the recent
updates, I've used it several times now and have found your examples very
helpful. I'll keep your description in mind when reading the PRB, it often
helps (me) to have a rough answer in mind when reading through the details.

On BandUP, I looked into this some months ago and found that the code could
not work with versions of QE past 6.3 (I think - maybe there was some
change to the output of pw.x after this version?). I've just looked at the
github page again (https://github.com/band-unfolding/bandup) and it has not
been updated yet, so still not compatible.

Thanks for your offer, I may contact you in the future,

Cheers

Will Hewett
Post Doctoral Researcher
Victoria University of Wellington
New Zealand



On Tue, Jan 5, 2021 at 10:34 AM Pietro Bonfa' <pietro.bonfa at unipr.it> wrote:

> Dear Will,
>
> the quantities computed by the code are presented in Phys. Rev. B 85,
> 085201 (2012).
>
> More precisely, you can collect the quantity in Eq. 8 (detailed in
> Appendix A) for the k points specified in input. Roughly speaking, that
> is the amount unfolded states with equivalent k vector contribute to the
> folded state at a given energy. Admittedly this is far from clear but
> the article mentioned above describes very accurately both the problem
> and the proposed solution. Still I hope that my awkward description will
> be sufficient to understand that, in a perfect supercell, this number
> depends on the degeneracy of the eigenvalue in the base cell. If the
> symmetry is low enough (and forgetting about spin), this number is
> either 0 or 1.
>
> The picture that you are sharing is actually Eq. 9, which is the
> quantity described above times a Dirac delta function of the energy,
> which is approximated with a Gaussian.
>
> As a consequence, the 'weight' in a perfect supercell depends on the
> degeneracy (or almost degeneracy) of a state, the discretization of the
> energy interval and the width of the Gaussian approximating the Dirac
> delta.
> I hope this partially answers your question.
>
> That being said, as you may have read, I've been always advocating for
> bandUP, since unfold.x was just my exercise to learn Fortran and the
> internals of QE.
> However, lately I found a little bit of time to fix some problems, add
> some tests and parallel execution, so I'm a little more confident than
> before on its correctness. Still let me remind you to carefully check
> your results and feel free to contact me for further details.
>
> Best regards,
> Pietro
>
> --
> Pietro Bonfà
> Department of Mathematical, Physical and Computer Sciences
> University of Parma
>
>
>
>
>
> On 1/3/21 5:37 AM, William Hewett wrote:
> > Hi all,
> >
> > I'm using QE to calculate the band structure of rare-earth nitride
> > materials, currently looking at the effect of nitrogen vacancies and the
> > resulting states created. I'm running calculations on 3x3x3 (primitive)
> > supercells, then using unfold.x to process the results.
> >
> > Unfold.x gives an output where each point (k,energy) also has a 'weight'
> > clearly this is zero where no states are present and non-zero where they
> > are present. My question is, what exactly is this weight? Some sort of
> > DOS for a single k-point?
> >
> > i.e. in the image below most points in the VB (near 6 on the y-axis) are
> > quite dark, while some points in the CB (flat 4f bands near -1) are
> > lighter in color.
> >
> > image.png
> >
> > Kind regards,
> >
> > Will Hewett
> > Post Doctoral Researcher
> > Victoria University of Wellington
> > New Zealand
> >
> >
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