[Wannier] Energy mismatch among symmetry equivalent states in silicon

[Nicola Marzari]

I guess you only need the occupied states, by temperature or doping, 
correct?

so, arash suggestion is the best one - playing with the window and the 
states included,
to try and get as much as possible a good beahviour with a coarse sampling.

another possibility is to use projections for the empty manifold, and do 
not do any
localization, to preserve the symmetry of the projections.

				nicola


On 02/09/2016 00:55, Vahid Askarpour wrote:
> If I understand you correctly, the only way to force the symmetry equivalent states to have identical energies is to use more k points.
>
> I am actually trying to apply symmetry in EPW to calculate the scattering rates for kpoints in the irreducible wedge and use symmetry to generate the scattering rates for the k points outside the wedge. However, I noticed that for silicon, the wannier-interpolated energies at symmetrically equivalent points are not identical.
> Increasing the k points, as you suggested, would increase the size of the electron-phonon matrix elements for the coarse grids (terabyte range) beyond our capability to store.
>
> It seems that I cannot use symmetry to simplify EPW calculations.
>
> Thank you so much for your insightful comments.
>
> Vahid
>
>> On Sep 1, 2016, at 7:11 PM, Nicola Marzari <nicola.marzari at epfl.ch> wrote:
>>
>> On 01/09/2016 21:27, Vahid Askarpour wrote:
>>> So with 8 bands, I get smaller spreads but the energy mismatch appears. It seems that I get better WFs with 8 bands than 4 bands. Or perhaps I am
>>> missing something here.
>>>
>>
>> Well, what does better mean? More localized allows for smoother
>> interpolation, but symmetry is also important.
>>
>> The part of the manifold that comes from conduction is disentangled
>> from a larger group of empty bands, and the resulting Wannier functions
>> do not satisfy the symmetries of the crystal.
>>
>> Of course, the more kpoints you use, the more you will force the
>> interpolation to go through the real calculated eigenvalues.
>>
>> 	
>> 			nicola
>>
>>
>> ----------------------------------------------------------------------
>> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
>> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
>> http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
>
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-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project