[Wannier] large spreeds for some WFs

[Arash A Mostofi]

Dear Hai-Ping

There are two things that might help:

(i) increase the number of conduction bands. If you're trying to obtain 
partially-occupied, out-of-plane p_z orbitals for your nanotube, you 
probably need to include bands that are at least 5eV or so above the Fermi 
level.

(ii) use the projections to give the dientanglement algorithm a good 
starting guess, eg, an s-type orbital on each bond and a p_z orbital on 
each atom.

Arash

On Thu, 23 Nov 2006, lan haiping wrote:

> Dear All,
>
> I am trying to  study  disentanglement of wannier with nanotube (10 0) by
> including several conduction bands.
> There are some problems  that i didnot come to for the cases of only valence
> bands included.
> First , it takes me long time to reach the convergence thread for
> disentangle process. I just tried to tune dis_mix_ratio , but there is no
> much effect.  In my calculation, I had included 130 bands for disentangling
> 100 WFs, it would take about 4000 iterations to reach convergence no matter
> what dis_mix_ratio i set to.  This value is of course seriouly larger than
> the default value (200).
> Though there are a few parameters for disentanglement, i donot have much
> idea about
> energy window settings for disentanglement and frozen energy window. Could
> we just set dis_win_min to conduction bands' bottom in my semiconducting cnt
> case  ?  I also tried to set frozen energy window , but there was no much
> effect for improving convergence. Could  the proper frozen energy window
> improve convergence ?  and would you please tell how to set up frozen energy
> window properly ?
>
> Another question is about large spreads for some WFs after
> wannierise.Afterwannierise process, there are mainly 3 groups of
> spreads of WFs. Spreads of
> first group are around 0.6- 0.7,  while 1.6-2.4 are for second group. There
> are 2 WFs for third group, of  spreads around 7.0 ,which are great larger
> than  that of other two group. Does such result have proper physical meaning
> ?
> Any comments will be appreciated.     As far as i know, large spreads of WFs
> may not be suitable for tight binding calculation . Are there any methods or
> settings to obtain smaller spreads of  WFs ?
>
> Best Wishes,
>
> hai-ping
>