[Wannier] Wannier functions in real space.

[Jonathan Yates]

On 8 Feb 2017, at 12:00, Oier Arcelus <oarcelus at hotmail.com> wrote:

> Hi forum,
> 
> I am trying to calculate the matrix elements of a LDA xc-potential in the wannier basis. The thing that comes to my mind is to take the wannier functions in a real grid that spans all the unit cell W(r), then get the xc-potential in that same grid and compute the values W(r1)* x V(r1) x W'(r1) for all r1 grid points in the unit cell. This would give me the matrix elements. However I encounter somre problems, the first one is obtaining the W(r). 
> 
> For this I just get W(r) with the seedname_00*.xsf XCrysDen files. But there are some problems, for some reason the centering of the real cell with the ones that contain the volumetric data is quite odd, looks like the lattice parameters are not totally the same, and when changin the file by hand the wannier functions get a bit shifted from the atomic centers. Another problem is that those files chop the wannier functions at the borders of the cell, and do not allow to those functions appear in the opposite site of the unit cell (due to periodic boundary conditions).

Oier,

 Plotting isn’t perhaps the most elegant feature of Wannier90. In part because we initially hoped the plotting would be done in the parent electronic structure code. 

If you haven’t already, look at the xsf spec
http://www.xcrysden.org/doc/XSF.html
One potential source of confusion is that xsf uses “General” grids, rather than periodic grids - so the first data point is repeated at the end.
Also look at the keyword wannier_plot_supercell which controls the size of the supercell in which the unit cell is plotted.

Wannier90 can also plot cube files - and this might make more sense for you. Look at the wannier_plot_radius keyword. One issue is that the code will only allow you to use cube format for orthorhombic unit cells. (I think because most cube readers don’t handle non-orthorhombic grids). However, given you just want the data you could try removing the check in parameters.F90 (c. line 1960) and see what happens. It also shouldn’t be difficult to adapt the code in plot.F90 to write out the WF in a format that suits you.

 I hope that gives you a few things to investigate, and come back to us if something is still puzzling 

Jonathan




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