[Wannier] about WFs' display

[Jonathan Yates]

On Tue, 29 May 2007, Arash A Mostofi wrote:

> I don't think your attachment made it through to my inbox, but the problem 
> you describe may be resolved by setting
>
> wannier_plot_supercell = 3


This is something of a FAQ, so maybe I can expand on the reasons behind 
Arash's answer.

Defns :  WF=Wannier Function  :   BZ=Brillouin zone

A WF is not periodic in the unit cell. Therefore it is not generally 
sufficient to plot it in a single unit cell.
  wannier_plot_supercell controls the number of units cell in which we 
construct the WF. For a value of 3 this means the home unit cell, and the 
26 neighbouring unit cells. This is normally sufficient to give a good 
picture of a WF.
  Plotting can be an expensive operation. You may wish to plot only a 
subset of the WF. You can control which WF are plotted using the 
wannier_plot_list keyword.

  The plotting of WF could be much improved. The next version of wannier90 
(due over the summer) will have improvements in this area.


  Another, related technical issue is that when the WF are computed from a 
finite sampling of the BZ they will be periodic in a supercell of the unit 
cell. For example a WF computed from a 4x4x4 sampling of the BZ will 
'live' in 4x4x4 supercell of the unit cell.
   This is apparent in Example 1 of Wannier90. If you plot WF in GaAs from 
a 2x2x2 BZ sampling using wannier_plot_supercell = 3 you will see the 
periodic images of the WF.


>> By the way, is there any way to generate multi-WFs in a single xsf file ?

  No.
   It would be trivial to make this modification. However, I don't think it 
would be very useful. As I understand it Xcrysden is able to plot a single 
isosurface, which maybe a weighted sum of several scalar fields, but not 
multiple isosurfaces (ie several WF at once). So putting all the WF in a 
single file would make Xcrysden very slow to start (it parses the entire 
xsf file on startup) to no real advantage.


  Jonathan


-- 
Dr Jonathan Yates         |    Theory of Condensed Matter Group
Corpus Christi College    |    Cavendish Laboratory
Cambridge, CB2 1RH, UK    |    Cambridge, CB3 OHE, UK
email jry20@cam.ac.uk     |    Tel +44 (0)1223 337461