[Wannier] Supercell size, b vectors or something else

[Jeil Jung]

Thank you Jonathan for your detailed explanation and feedback. 
Things worked out after the fix.
Jeil

On Aug 7, 2012, at 12:37 PM, Jonathan Yates wrote:

> Jeil,
> 
> The difference between the 'good' and 'bad' results is due to the number of bands from which the optimal subspace is selected (i.e. nbnd in the nscf calculation). By chance I had 20, yours was 10.
> 
> There is a 'chemical' reason for this: First, notice that it is the pz WF which start with a large spread in the nbnd=10 case. Then focus on the bands at gamma. We need enough bands to reach the pi* state. For AA-stacked graphite 10 bands is sufficient. However, as we make a larger supercell 'free-electron' like vacuum states fall below the pi* state. The larger the supercell the more of these bands. At some point the pi* state does not lie within the lowest 10 bands. The MLWF routine does the best it can to form localised WF, but the symmetry is broken.
> 
> So if you change nbnd to 20 in your runs you will get symmetric MLWF. For a really big cell it might need to be larger than this - if you do a calculation at gamma and gamma+(a bit) you can see where the pi* state is.
> 
> Thanks for the interesting question!
> 
> Jonathan
> 
> 
> On 7 Aug 2012, at 16:50, Jeil Jung wrote:
> 
>> Hi Nicola and Jonathan,
>> Thanks for your suggestions. I tried first to reproduce Jonathan's results look great, unlike those that I am getting. 
>> The results I get for c = 20 \AA are
>> 
>> ------------------------------------------------------------------------------
>> Initial State
>>  WF centre and spread    1  (  0.357549,  1.840705,  4.999300 )     0.60827442
>>  WF centre and spread    2  (  0.357547,  0.619293,  4.999290 )     0.60825884
>>  WF centre and spread    3  (  1.415324,  1.230001,  4.999302 )     0.60826060
>>  WF centre and spread    4  (  0.710151,  1.230129,  4.952752 )     3.27122735
>>  WF centre and spread    5  ( -0.000082,  0.000298,  4.905977 )     3.34246618
>>  Sum of centres and spreads (  2.840489,  4.920426, 24.856621 )     8.43848738
>> 
>>      0     0.844E+01     0.0000000000        8.4384873837       1.19  <-- CONV
>>        O_D=      2.0391342 O_OD=      2.8651740 O_TOT=      8.4384874 <-- SPRD
>> ------------------------------------------------------------------------------
> 
> 
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