[Wannier] [Three Question about wannier90 program]

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Dear wannier users,

I have three questions regarding Wannier90 program. I'd appreciate it if you could share similar experiences or advice.

1. DFT Band vs. Wannier Band Energy Discrepancies
 When calculating the DFT band and the Wannier band and directly comparing the energies at the same k-point for each band, a difference of approximately 1.0d-1 to 1.0d-8 eV is observed. Generally, what level of error is considered "well-Wannierized"? (Of course, the k-point sampling matches. Looking at the Wannier90 tutorial file, there's a noticeable difference between the DFT band and the Wannier band plot. If it's visible in the figure, it must be a fairly large energy difference. Is this correct?)

2. Semiconductor calculations
 In semiconductor systems, the valence bands are often well-matched, but the conduction bands are not. What are the main causes of this problem? Also, the common advice is to "include a small range of CBM in the frozen window." Is this the right approach?

3. GW interpolation
 When performing GW interpolation, the example spread sometimes appears abnormally large, as shown below. Are there any practical methods or tips for reducing the spread in these situations?

example)
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 Final State
  WF centre and spread    1  (  0.372766,  0.271454,  0.100115 )     8.87768007
  WF centre and spread    2  (  0.346249,  0.302240,  0.077516 )     8.52974539
  WF centre and spread    3  (  0.956188, -1.596142, -1.585203 )     6.79466576
  WF centre and spread    4  (  0.846529, -1.265707, -1.314245 )     6.88845477
  WF centre and spread    5  ( -1.559035,  0.934612, -1.539765 )     6.84836086
  WF centre and spread    6  ( -1.485984,  0.895648, -1.506476 )     6.84063641
  WF centre and spread    7  (  0.001865, -0.046586, -0.038040 )     6.32797742
  WF centre and spread    8  ( -0.015611,  0.007019, -0.016586 )     6.19032592
  WF centre and spread    9  (  2.736587,  2.395840,  2.681191 )     3.32470432
  WF centre and spread   10  (  2.708292,  2.346611,  2.696151 )     3.54016326
  WF centre and spread   11  (  3.978830,  2.338176,  2.495150 )    11.21574562
  WF centre and spread   12  (  4.065804,  2.432744,  2.491568 )    10.51734314
  WF centre and spread   13  (  2.407247,  2.765620,  2.725119 )     3.10145325
  WF centre and spread   14  (  2.507236,  2.783624,  2.679231 )     2.94491143
  WF centre and spread   15  (  2.416386,  3.956995,  2.508559 )    12.16683265
  WF centre and spread   16  (  2.547707,  3.808478,  2.527233 )    13.94873621
  WF centre and spread   17  (  2.799901,  2.787311,  2.490126 )     2.72683243
  WF centre and spread   18  (  2.752923,  2.802438,  2.557549 )     2.64088968
  WF centre and spread   19  (  2.603858,  2.616160,  3.779997 )    14.13766140
  WF centre and spread   20  (  2.670033,  2.661026,  3.723072 )    14.56538142
  WF centre and spread   21  (  1.847802,  1.851559,  7.111413 )     6.21201839
  WF centre and spread   22  (  1.919903,  1.792560,  7.134523 )     6.13615812
  WF centre and spread   23  (  7.062253,  1.721907,  2.052594 )     9.15177271
  WF centre and spread   24  (  5.666186,  0.286729,  2.746048 )     6.62187501
  WF centre and spread   25  (  0.221796,  5.652035,  2.778891 )     6.70473982
  WF centre and spread   26  (  1.704720,  7.043909,  2.077182 )     8.93031270
  WF centre and spread   27  (  1.185488,  1.174497,  3.638038 )     1.59968796
  WF centre and spread   28  (  1.185512,  1.174349,  3.638713 )     1.60317424
  WF centre and spread   29  (  3.650511,  1.159018,  1.159550 )     1.42725534
  WF centre and spread   30  (  3.649241,  1.159410,  1.159591 )     1.42553039
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You don't have to answer every question. Feel free to share your experiences and know-how, as it would be very helpful.

Best regards,
GiMyung Park
Yonsei University
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