[Wannier] parameter to control convergence

[Tadashi Ogitsu]

Hello,

I've just started to use the wannier90 code, and having a little  
problem in converging the Wannier functions, so, I would appreciate  
very much if you could give me a little bit of tips in controlling  
the convergence.

What I need is the Wannier centres and its spreads for beta- 
rhombohedral boron crystal. The system is a little bit big, 105 boron  
atoms in the rhombohedral unit cell (this is not exactly the  
experimental structure but that is another story. So, let me call it  
*beta-boron* in this email). The electronic structure of the *beta- 
boron* is metalic so that I'm using the disentanglement scheme  
developed by SMV (thanks Ivo!). I've put 180 bands, and the Fermi  
level is at around 158th band (this is metal). So, I specify  
num_bands = 180 and num_wann = 158. I've also specified the  
dis_froz_max equal to the Fermi level given by the PWSCF 3.1.1.

The code seems to be working correctly, I mean, I do NOT see any  
warning (besides, "name = wann_main not found in io_stopwatch" when I  
restart the job from checkpoint), and the last message is "All done:  
wannier90 exiting".

I've made iterations up to a little over 300, and the individual  
spreads are certainly decreasing, mostly down to 1.4-1.5, looking  
like reasonable. DLTA parameters go down to 10^(-4). However, there  
are 4 wannier centres, whose spreads are unusually large, around 55,  
and they do not decrease.

So, my question is, which parameter shall I change to improve the  
convergence?

FYI: I've tested with alpha-rhombohedral boron, which consists of 12  
boron atoms in the rhombohedral cell. This converged without any  
problem, and the results, i.e. the locations of Wannier centres and  
its spreads look perfectly reasonable. This system is an insulator so  
that it does not require the disentanglement procedure though.

I'm looking forward to hearing your suggestions. Thanks.

By the way, the system size is very large as you might notice, so, I  
think, it is a quite challenging problem but the code seems to be  
dealing very well (besides the convergence). I'm very impressed.

Best,
Tadashi Ogitsu
#I might be observing a memory leak but I'll post it when I get more  
accurate information if it comes from the computer or the code.