[Wannier] spread

[Vivek Ranjan]

I had asked the following question a few days back. I am trying to
calculate wannier function of BN sheet.
(i) I have a hard time reaching convergence. In about ten thousand
steps the spread seem reasonable. However, if I run longer, spread
increases once again on one of the sites (around 15 A).

(ii) There is no problem in convergence if the BN-plane is staggered.

(iii) I have attached one diagram with the mail. I asked for
"B:sp2;pz" in projections. But it seems to be centered on N (green)
and spread over three B (yellow). Seems like a large spread ?

(iv) The diagram depicts three wannier functions. I want only one....
How do I get rid of these images of the central one ?

I would appreciate some suggestion.

Thanks,

Vivek
Physics, NCSU

On Fri, May 30, 2008 at 4:38 PM, Vivek Ranjan <vranjan at ncsu.edu> wrote:
> Hello,
>
> I am trying to calculate wannier function of BN sheet. The way the unit
> cell is constructed, I have chosen (12,1,1) kpoint mesh for scf
> calculation. Then I do an nscf calculation with 4 kpoints (4,1,1). The
> spread of one of wannier function is 26 A. I run several steps (more than
> 20000) and still it does not converge. The question is how to reduce this
> spread ?
>
> I tried putting more kpoints by doing (12,2,2) scf calculations and 16
> kpoints (4,2,2) for nscf and wannier parts. The problem is instead of 16
> kpoints in the nscf that I hand put in the file, pwscf always generates 24
> kpoints. The additional kpoints are shifted kpoints that I put. It never
> happened to me before and wondering why it is happening ?
>
> (12,1,1) scf, and (4,1,1) kpoints has no such problems.
>
> Thanks,
>
> Vivek,
> Physics, NCSU.
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