[Wannier] convergence problem in construction of WF

[Lin Xie]

Dear Jonathan
    I've solved this problem by changing the initial guess 3p orbitals of S
to hybridized sp3 orbtials and everything works fine with the 7x7x2 mesh
now. Also, the Hamiltonian is exactly real. But when I compared the results
with the "bad" one (both obtained with 7x7x2 mesh), I found that the "good"
MLWFs I got now is almost identical to the "bad" one. Furthermore, their
spread difference is only within 1%. It's quite amazing. Anyway, thank you
very much for your kind suggestions.

Best regards!


On Mon, Jun 3, 2013 at 8:13 PM, Jonathan Yates <
jonathan.yates at materials.ox.ac.uk> wrote:

>
> On 2 Jun 2013, at 11:51, Lin Xie wrote:
>
> > Dear all
> >    I'm using Fleur+Wannier90 and want to get the WF basis for the
> valence band of MoS2. The SCF is converged with a 7x7x2 M-P mesh and I have
> no problem in getting the maximally localized Wannier functions with a
> 5x5x2 mesh. Moreover, the Hamiltonian matrix is real for the 5x5x2 mesh,
> indicating that the WFs are optimized. However, when I try to get the MLWFs
> with a denser mesh, e.g. a 7x7x2 mesh, the spread is about 10% larger than
> that with the 5x5x2 mesh. Also, there is imaginary part in the Hamiltonian
> matrix with the 7x7x2 mesh. Can anyone tell how to overcome this problem?
>
> Lin Xie,
>
>  Let me make a couple of general comments that might help.
>
> First, note that our representation of the spread operator converges
> slowly with the density of the k-point grid. So you may well find that your
> Hamiltonian in the MLWF basis is well converged at 5x5x2 (ie the wannier
> interpolated bands are a good match to those directly from Fleur). The
> spread of the MLWF is not a good parameter to check k-point convergence
> with - unless you need to use the spread. In that case you may need to do
> something more advanced (see sections I.C.2 and II.F.2 of Rev Mod Phys 84,
> 1419 )
>
> Second, as you increase the density of the k-point mesh the minimiser has
> to work harder to localise the MLWF. This might explain why there is some
> imaginary component to the MLWF for the denser mesh. Have you looked at the
> WF from the 5x5x2 calculation - do they look like the start guess? Can you
> use this information to improve the start-guess for the 7x7x2 case? Is the
> imaginary component quite small - if you simply ran for more iterations
> does it get smaller?
>
>  Jonathan
>
>
>
>
>
> --
> Department of Materials, University of Oxford, Parks Road, Oxford, OX1
> 3PH, UK
> tel: +44 (0)1865 612797                http://users.ox.ac.uk/~oums0549/
>
> _______________________________________________
> Wannier mailing list
> Wannier at quantum-espresso.org
> http://www.democritos.it/mailman/listinfo/wannier
>



-- 
Lin Xie
Beijing National Center for Electron Microscopy
Department of Material Science and Engineering
Tsinghua University
Beijing, PR of China
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/wannier/attachments/20130604/a9de7011/attachment.html>