[Wannier] parameter to control convergence

[Tadashi Ogitsu]

Good evening,

1. I have found that those MLWFs with unusually large spread vanish  
if I increased the k-points grid  size. I was using 2x2x2 before and  
now I'm using 4x4x4. Does it make sense? (Now, all of the MLWFs look  
reasonably localized)

#Since the unit-cell size is big with beta-boron, I thought 2x2x2  
grid is not that bad, but this seems to tell me that I cannot go  
cheap...

2. Also, at the beginning, I've mentioned about a possibility of  
memory leak. It seems that, memory size grow very much if I turn on  
wannier_plot. It grew rapidly after running for awhile, so, I  
suspected the memory leak initially. I found out later that if I  
switch off the option, the memory size stays around 100MB. Now, I'm  
guessing that turning on this option simply allocates large memory  
space. In my case, the original basis size were 66^3 FFT grid times  
180 bands and, at that time, 2x2x2 kpoints.

My firs question on this issue is that, does the wannier_plot indeed  
require larger memory size? Then, how can I estimate the size?

In that particular case, the job crashed after awhile, and the  
machine has 32GB memory, so it looks like, it went over 32GB!

#I would imagine that the memory size would be estimated something  
like (FFT grid)*(# bands)*(# of kpoints) *prefactor. I would like to  
know the prefactor if this assumption is correct.

Thanking in advance!

Best,
Tadashi



On Aug 23, 2006, at 12:35 PM, Jonathan Yates wrote:

> On Wed, 23 Aug 2006, Tadashi Ogitsu wrote:
>
> Hi Tadashi,
>
>  Thanks for telling us about your Boron calculations.
>
>  I'd like to make a fairly general comment. But I think it might be  
> at the root of your question.
>
>  If we look at the valence states of an insulator then the MLWF are  
> determined by the localisation criteria. The MLWF are "fully  
> occupied", by which I mean that the sum of |w(r)|^2 over all of the  
> WF gives the charge density. Here it is certainly valid to think  
> about the bonding in terms of the MLWF.
>
>  When we use the disentangling procedure (ie for a metal or to  
> describe both valence and conduction states in a insulator) the  
> MLWF are defined not only by the localisation criteria, but also by  
> the dimension of the optimal subspace (ie the number of WF) and the  
> ranges of the two energy windows.
>  The MLWF are no longer fully occupied, we have "partially- 
> occupied" MLWF. So now the sum of |w(r)|^2 over all of the WF is  
> the not the charge density. Using these MLFW to interpret the  
> bonding in metals is therefore not straight-forward. [which is to  
> say that you need to think about how this issue affects your  
> particular problem.]
>
>> Do the occupation given in the pwscf calculations used in  
>> Wannier90 code? or in Wannier90, only eigenfunctions from the  
>> pwscf output are used and the energy window to construct the  
>> Wannier functions (or the definition of subspace for the unitary  
>> transformation?) is determined only by dis_*_[min|max] parameters?  
>> Thanks a lot!
>
>  You are correct, Wannier90 does not know anything about the  
> occupation of the bloch states. The energy windows are determined  
> by the dis_*_[min|max] parameters. One must also specify the number  
> of WF to extract.
>
>  There is a keyword called 'fermi_energy'. This is not used in the  
> construction of the WF. It is used when generating a plot of the  
> Fermi surface using Wannier interpolation [eg /cond-mat/0608257].
>
>  Yours
>   Jonathan
>
> -- 
> Dr Jonathan Yates:  email: jryates at lbl.gov   phone: 510-642-7302
> Material Science Division, Lawrence Berkeley National Laboratory  and
> Department of Physics, University of California,
> 366 Le Conte Hall #7300, Berkeley, CA 94720-7300, USA
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