[Pw_forum] Re: Different Gamma factors for Q-points in the same star

[Stefano Baroni]

Andrea, Eyvaz: I know nothing about the way the Eliashberg function  
is calculated in Quantum ESPRESSO, but symmetry issues have (should  
have) little (if anything) to do with k-point grids, cutoff, and the  
like. What I mean is that if symmetrization is well implemented (and  
well understood by those who use the code) an inadequate cutoff and/ 
or k-point grid may well give inaccurate results, but these results  
should be the same (to _very_ high accuracy) whether calculated by  
restricting the BZ sampling to the irreducible wedge (and properly  
symmetrizing the result), or by the extending the sum to the full BZ.  
Sorry for not being more helpful than this - Stefano

On May 29, 2006, at 7:40 AM, Andrea Marini wrote:

> On Mon, 29 May 2006, Eyvaz Isaev wrote:
>
>>> the results do  not change if I increase the
>>> cutoff to 32 Ry and
>>> use a 6 6 6 MP grid.
>>>
>> Actually 25 Ry should be enough. I think there is not
>> too much difference between 4x4x4 and 6x6x6 k-grid (8,
>> and 16 k-points including gamma-point). How about
>> 12x12x12 or 16x16x16?
>
> No better results. These are the .elph files using a 12 12 12 grid.
>
>      0.25000000     0.75000000    -0.25000000      10       3
>   0.271070E-05  0.427079E-05  0.734232E-05
>      Gaussian Broadening:   0.100 Ry, ngauss=   1
>      DOS =  2.626188 states/spin/Ry/Unit Cell at Ef=  8.283160 eV
>      lambda( 1)=  0.1696   gamma=   12.48 GHz
>      lambda( 2)=  0.1114   gamma=   12.91 GHz
>      lambda( 3)=  0.1656   gamma=   33.01 GHz
>
>
>      0.25000000    -0.25000000     0.75000000      10       3
>   0.271070E-05  0.427086E-05  0.734185E-05
>      Gaussian Broadening:   0.100 Ry, ngauss=   1
>      DOS =  2.626188 states/spin/Ry/Unit Cell at Ef=  8.283160 eV
>      lambda( 1)=  0.0859   gamma=    6.32 GHz
>      lambda( 2)=  0.2025   gamma=   23.47 GHz
>      lambda( 3)=  0.1435   gamma=   28.60 GHz
>
> Thanks for your help
>
> Andrea
>
> ---------------------------------------------------------------------- 
> ----
>                                Andrea MARINI
>
>        Physics Department, University of Rome "Tor Vergata" (Italy)
>               - phone: +39-0672594894 - fax: +39-062023507 -
>
> -- andrea.marini at roma2.infn.it - http://www.fisica.uniroma2.it/ 
> ~marini/ --
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
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