[Wannier] A question on the Hamiltonian with spinors from Wannier90

Wed Nov 14 18:29:35 CET 2012

Dear Julen

Thank you for your suggestions. Finally, I have got a satisfying Hamiltonian, which respects the time-reversal symmetry.
In my case, the convergence of DFT calculation is found to be a problem. Wannier90 requires wavefunctions on a full k-point grid, while my DFT calculation uses a reduced k-points and interpolates  the wavefunctions to a full k grid. Here the interpolated wavefunction and eigen energies are not accurate enough. (For calculations without spinors, normal interpolation is found to be enough) Therefore, I switch off the symmetry and use a full k-grid to extract the wannier parameters. Consequently, this improves  my wannier90 results dramatically.
This might be a well-known trick for wannier90. However, I spent a lot of time to realize it.

BTW, I knew that the imaginary parts of _hr.dat are zero for calculations without SOC. However, my SOC hr.dat still has the imaginary components.

All the best,
Binghai
________________________________________
From: julen.azpiroz at gmail.com [julen.azpiroz at gmail.com] on behalf of Julen Ibanez Azpiroz [julen.ibanez at ehu.es]
Sent: Monday, November 12, 2012 9:01 PM
To: Yan, Binghai
Cc: wannier at quantum-espresso.org
Subject: Re: [Wannier] A question on the Hamiltonian with spinors from Wannier90

Dear Binghai,

Maybe the issue is related to the convergence, the off-diagonal matrix elements you show have a non-null imaginary part, as far as I know this means that the Wannier functions you got are not still the maximally localized ones since these should be real in a system with TR symmetry (see PRL 98, 046402 (2007)). Maybe you could try to wannierise till the imaginary part of the matrix elements are null to be sure that you got the MLWF, and then check the on-site and off-diagonal matrix elements. Just a question, the 16 bands you are including, are they all below the Fermi level?

Cheers,

Julen

On Fri, Nov 9, 2012 at 11:44 AM, Yan, Binghai <yanb at uni-mainz.de<mailto:yanb at uni-mainz.de>> wrote:
Dear Wannier developers

I am new user of wannier90. I extract wannier functions from a DFT calculation (I use vasp) including spin orbit coupling (SOC). Then I switch on spinors=T and double the num_bands.
My systems have no spin polarization, respecting the time reversal symmetry. A wannier function is expected to be represented by two functions, which have the same center but different spins. I expect these two functions have the same onsite energies and the hopping term between them are exactly zero.
However, I get different onsite energies and nonzero hopping terms, although the band structure is well reproduced. The wannier cenceters are also very different.

The following is an example of my inputs for bulk HgTe calculations. (zincblende structure)

==========
num_wann          =   16
num_bands         =   38
#exclude_bands     =   3-12

dis_win_max       =  15.0
dis_froz_max      =  9
dis_num_iter      =  2000
dis_mix_ratio     = 1.d0

num_iter          = 1000
num_print_cycles  = 10

Begin Projections
Hg : sp3
Te : sp3
End Projections

spinors = .true.

begin unit_cell_cart
     3.2300000     3.2300000     0.0000000
     0.0000000     3.2300000     3.2300000
     3.2300000     0.0000000     3.2300000
end unit_cell_cart

begin atoms_cart
Hg       2.4225000     2.4225000     2.4225000
Te       4.0375000     4.0375000     4.0375000
end atoms_cart

mp_grid =    12    12    12

begin kpoints
      0.000000000000      0.000000000000      0.000000000000
      0.083333333333      0.000000000000      0.000000000000
      0.166666666667      0.000000000000      0.000000000000
      0.250000000000      0.000000000000      0.000000000000
................
========================

The optimized wannier centers are :
 Cycle:   1000
  WF centre and spread    1  (  1.125081,  2.105459,  2.107134 )     7.50544434
  WF centre and spread    2  (  2.108857,  1.123510,  2.103942 )     7.50493864
  WF centre and spread    3  (  2.106035,  2.107794,  1.122418 )     7.50768700
  WF centre and spread    4  (  1.124096,  1.124214,  1.123910 )     7.52064335
  WF centre and spread    5  (  3.522963,  3.524601,  3.524535 )     4.48040046
  WF centre and spread    6  (  3.526018,  2.934456,  2.939037 )     4.47399171
  WF centre and spread    7  (  2.939672,  3.523541,  2.932669 )     4.46863560
  WF centre and spread    8  (  2.934153,  2.938291,  3.522491 )     4.47010302
  WF centre and spread    9  (  2.107155,  2.105137,  1.125272 )     7.64204572
  WF centre and spread   10  (  1.123133,  1.123929,  1.123907 )     7.64532973
  WF centre and spread   11  (  1.122550,  2.106696,  2.105047 )     7.63263662
  WF centre and spread   12  (  2.104217,  1.123646,  2.107754 )     7.63564195
  WF centre and spread   13  (  3.524860,  3.524017,  3.523515 )     4.51698438
  WF centre and spread   14  (  3.522838,  2.936705,  2.934278 )     4.51145886
  WF centre and spread   15  (  2.933391,  3.524025,  2.938085 )     4.50864047
  WF centre and spread   16  (  2.937251,  2.934720,  3.525198 )     4.51260402
  Sum of centres and spreads ( 38.762270, 38.760740, 38.759191 )    96.53718585

For example, the matrix elements between WF 8 and WF 16 are

    0    0    0    8    8    0.863620    0.000000
-
    0    0    0   16   16    0.932080    0.000000
-
    0    0    0   16    8   -0.032312   -0.000905
-
    0    0    0    8   16   -0.032312    0.000905

Is this problem due to a bad projection? Actually, I used sp3 for non-SOC case, it seems pretty well.
Is there a way to constrain different spins have the same wannier centers?

Thank you very much in advance!
Binghai

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========================================
 Julen Ibañez Azpiroz
 Materia Kondentsatuaren Fisika Saila
 Zientzia eta Teknologia Fakultatea
 Euskal Herriko Unibertsitatea
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