[Wien] fold2Bloch Question - Missing data points

[Oleg Rubel]

Hello Tristan,

I see your difficulty. The generation of the k-path for unfolding is a 
bit tricky. For instance, if you want to see [(0,0,0) -> (1/2, 0, 0)] 
section after unfolding, your *.klist file should include points [(-1/2, 
0, 0) -> (1/2, 0, 0)] to generate *.vector file. It sounds 
counter-intuitive from a regular band structure plot point of view. 
However it helps to think of the primitive Brillouin zone a set of small 
'tiles'. Each tile is a supercell BZ. When the k list is limited to 
[(0,0,0) -> (1/2, 0, 0)] points, only half of the tile is meshed. When 
tiles are put together to form the primitive BZ, you will see 'gaps' in 
the mesh in place of the missing part [(-1/2, 0, 0) -> (0,0,0)].

Please check this tutorial
https://github.com/rubel75/fold2Bloch-Wien2k/wiki/Tutorial-1:-Lattice-of-Hydrogen-atoms

When path gets complicated, generation of the *.klist file becomes not 
straightforward. There is a Matlab script to assist with generating the 
k path for unfolding
https://github.com/rubel75/fold2Bloch-VASP/blob/master/utils/fold.m
It generates the list of k points in VASP format because it is simple, 
but you can get the idea and edit *.klist file accordingly.

I hope it is not very confusing.

Best regards
Oleg

-- 
Oleg Rubel (PhD, PEng)
Department of Materials Science and Engineering
McMaster University
JHE 359, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada
Email: rubelo at mcmaster.ca
Tel: +1-905-525-9140, ext. 24094
Web: http://olegrubel.mcmaster.ca

On 3/27/2019 3:59 PM, de Boer, Tristan wrote:
> Hi,
> 
> I'm trying to use fold2Bloch to compare the band diagrams of graphite
> and 4x4x1 supercells of graphite (with an expanded c-axis). I've made
> the supercells 1_P1 with a hexagonal geometry (a=b, gamma=120 deg) by
> making each atom unique so that the Brillouin zone has the same shape as
> graphite.
> 
> I've selected a k-path for the supercell case [(0,0,0) -> (1/3, 1/3, 0)
> -> (1/2, 0, 0) -> (0,0,0)] in xcrysden. The output klist_band file looks
> OK. I've run x lapw1 -band -p, x joinvec, and followed the directions in
> the guide. When I run fold2Bloch itself (with 4:4:1 folding input) there
> don't appear to be any problems, and I get feedback that the klist
> matches the vector file.
> 
> The issue I'm having is that using the ubs_dots.m file (having G to
> match the supercell, the k-path and the folds to [4, 4, 1]) yields a
> plot that looks correct, except that between the critical points there
> are these large gaps in the data. I've tried changing the k-path to a
> single line, but this didn't fix the issue. Increasing or decreasing the
> number of k-points in the band calculation also didn't fix the issue.
> 
> I've plotted the first three columns of the case.f2b file, and there
> appear to be discontinuities, but I'm not sure if this is an issue. I'm
> running WIEN2k 17.2 on linux compiled with ifort. Any suggestions or
> comments would be appreciated.
> 
> Best Regards,
> 
> Tristan
> 
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