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

[Pietro Bonfa']

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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