[Wannier] band structure interpolation ends up with wiggly bands

[Yu Zhang]

Dear Aron,

Thank you for your detailed explanations and suggestions. I will tried it
out.

I have no idea of why your wannier functions are more compact for super
cell. I usually use primitive cell instead of supercell. Does anyone have
clue on Aron's issue?

Best

Yu

On Thu, Feb 12, 2015 at 7:30 AM, Aron Szabo <szaboa at iis.ee.ethz.ch> wrote:

>  Dear Yu,
>
> I was also working on gold recently. As Nicola said, you should include
> the lowest two bands too. The other thing is that you should use the
> disentanglement method instead of just excluding the topmost bands, because
> they are entangled. When you exclude the n-th band it means that at every
> k-point the state with the n-th energy is excluded. It is not what you want
> when bands are crossing each other, because e.g. at the W point in your
> band structure you should keep the topmost blue line because that is the
> one "smoothly connected" to the lower energy states, although it has a
> higher energy at W than the other below it that you should exclude. The
> disentanglement method finds these optimally connected bands. The third
> thing is that you should try to set an sp3 hybrid as an initial projection
> instead of the s orbital. I found that it converges better. The center of
> this Wannier function should move away from the gold atom, but if you
> choose an s orbital centered on the atom, it will stay in a local minimum
> due to it's symmetry. So I would recommend these settings:
>
> num_wann  = 12
>  num_bands = 16
>
> dis_froz_max = 2
> #dis_froz_min = -2
> dis_win_max = 7
>
> spinors = .true.
> Begin Projections
> Au: sp3-1;l=2
> End Projections
>
>
> You can also set a value for dis_froz_min, though it's not absolutely
> necessary. The default is just the lowest energy. States between
> dis_froz_min and dis_froz_max will be reproduced exactly by the
> Wannierization, but usually the larger interval you set, the larger the
> spread of the Wannier functions will be, due to the more constraint.
> Therefore you should set it only around those energies that you need to
> reproduce exactly, e.g: close to the Fermi energy if you want to calculate
> transport later.
>
> There is just one strange thing I've found and don't know why it happens:
> if I create a 4-atomic cubic cell instead of the primitive 1-atomic FCC
> cell, I get somewhat more compact Wannier functions with the exact same
> settings. Does anyone have a clue why is that? I've observed it in many
> cases that if I create a supercell with a different space group than the
> primitive cell (e.g. a rectangular cell made of two hexagonal unit cells of
> MoS2) the Wannierization might fail. And now it's the opposite, I get
> better results with a supercell.
>
> Best,
> Aron Szabo
>
>
> On 02/12/2015 05:16 AM, Yu Zhang wrote:
>
> Dear wannier90 users and developers,
>
>  I am using wannier90-1.2 and vasp5.3 to obtain the wannier wave function
> of gold with spin-orbital coupling. I used d5s orbital as target. However,
> it ends up with some wiggly bands as shown by the attached figure. I have
> tried different projection (d5), and k-mesh, but I still failed to get the
> smooth bands. Does anyone know what causes the wiggly bands and how to get
> rid of them?
>
>
>  My wannier90 input file is:
> ===========================================
>  num_wann  = 12  ! set to NBANDS by VASP
> num_bands = 12
>
>  exclude_bands : 1-2, 15-16
>
>  spinors = .true.
> Begin Projections
> Au: l=0;l=2
> End Projections
>
>  begin unit_cell_cart
>      0.0000000     2.0340000     2.0340000
>      2.0340000     0.0000000     2.0340000
>      2.0340000     2.0340000     0.0000000
> end unit_cell_cart
>
>  begin atoms_cart
> Au       0.0000000     0.0000000     0.0000000
> end atoms_cart
>
>  mp_grid =    21    21    21
>
>  begin kpoints
>       0.000000000000      0.000000000000      0.000000000000
>       0.047619047619      0.000000000000      0.000000000000
>       0.095238095238      0.000000000000      0.000000000000
>       0.142857142857      0.000000000000      0.000000000000
>       0.190476190476      0.000000000000      0.000000000000
> .......
>  ==================================================
>
>  Thank you very much in advance!
>
>  Best regards,
>
>  Yu Zhang
>
>
> _______________________________________________
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>
>
>
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