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

[Eyvaz Isaev]

Hi Andrea,

At least your k-points set looks very-very small for
electron-phonon coupling constants calculations. Try
increase number of k-points.
It is worth increasing ecutwfc, too (say, up to 20-25
Ry).

Bests,
Eyvaz.

--- Andrea Marini <Andrea.Marini at roma2.infn.it> wrote:

> Dear users,
> 
>  	I am a newbie in using pw/ph to get
> electron-phonon coupling 
> matrix elements (ME).
> 
> Now I have the following problem. To understand the
> ME symmetry properties 
> I have done two calculations of the Eliashberg
> function for Al using a 
> Monkhorst-Pack set of Q-points in the whole BZ and
> only in the irreducible 
> wedge and I have found tiny (but not negligible)
> differences in the two 
> calculations.
> 
> I have traced back the problem to different Gamma
> factors (calculated  in 
> elphonon.f90) for two Q-points in the same star.
> This confuses me as I was 
> expecting possible differences only  for degenerate
> modes.
> 
> Am I wrong ? Am I doing sone stupid mistake ?
> 
> THANKS!
> 
> Andrea
> 
>  
>
**************************************************************************
> 
>       q = (    0.250000000   0.750000000 
> -0.250000000 )
> 
>       omega( 1) =       2.619122 [THz] =     
> 87.365086 [cm-1]
>       omega( 2) =       3.738457 [THz] =    
> 124.702317 [cm-1]
>       omega( 3) =       4.666853 [THz] =    
> 155.670490 [cm-1]
> 
>       Gaussian Broadening:   0.100 Ry, ngauss=   1
>       DOS =  4.376674 states/spin/Ry/Unit Cell at
> Ef=  8.063192 eV
>       double delta at Ef = 33.847218
>       lambda( 1)=  1.2622   gamma=   36.19 GHz
>       lambda( 2)=  0.9349   gamma=   54.61 GHz
>       lambda( 3)=  0.3583   gamma=   32.61 GHz
> 
>  
>
**************************************************************************
> 
>       q = (    0.250000000  -0.250000000  
> 0.750000000 )
> 
>       omega( 1) =       2.619570 [THz] =     
> 87.380025 [cm-1]
>       omega( 2) =       3.738907 [THz] =    
> 124.717352 [cm-1]
>       omega( 3) =       4.666851 [THz] =    
> 155.670416 [cm-1]
> 
>       Gaussian Broadening:   0.100 Ry, ngauss=   1
>       DOS =  4.376674 states/spin/Ry/Unit Cell at
> Ef=  8.063192 eV
>       double delta at Ef = 33.847218
>       lambda( 1)=  1.7620   gamma=   50.53 GHz
>       lambda( 2)=  0.9916   gamma=   57.94 GHz
>       lambda( 3)=  0.1641   gamma=   14.93 GHz
> 
> To obtain these results I have used
> 
> pw.x< Al.scf.in
> pw.x< Al-1.nscf.in
> ph.x< Al-1.ph_elph.in
> 
> for q =  0.250000000   0.750000000  -0.250000000
> 
> and
> 
> pw.x< Al.scf.in
> pw.x< Al-2.nscf.in
> ph.x< Al-2.ph_elph.in
> 
> for q =  0.250000000  -0.250000000   0.750000000
> 
>   = Al.scf.in
>
=============================================================
>   &control
>      calculation = 'scf',prefix='Al',
>      pseudo_dir =
>
'/home/marini/Sources/espresso/espresso-3.0/pseudo/',
>      wf_collect=.true.,
>   /
>   &system
>      ibrav=  2, celldm(1) =7.50, nat=  1, ntyp=
> 1,ecutwfc = 16, nbnd = 5,
>      occupations='smearing', smearing='mp',
> degauss=0.022
>   /
>   &electrons
>      diagonalization='david'
>      conv_thr = 1.0d-10
>   /
> ATOMIC_SPECIES
>   Al  26.98  Al.vbc.UPF
> ATOMIC_POSITIONS
>   Al 0.00 0.00 0.00
> K_POINTS {automatic}
>    4 4 4 0 0 0
> 
>   = Al-1.nscf.in
>
==========================================================
>   &control
>      calculation='phonon',prefix  = 'Al'
>      pseudo_dir =
>
'/home/marini/Sources/espresso/espresso-3.0/pseudo/',
>   /
>   &system
>      ibrav=  2, celldm(1) =7.50, nat=  1, ntyp=
> 1,ecutwfc = 16, nbnd = 5,
>      occupations='smearing', smearing='mp',
> degauss=0.022
>   /
>   &electrons
>    diago_thr_init =  1.0d-6
>   /
>   &phonon
>      xqq(1)= 0.25  , xqq(2)= 0.75 , xqq(3)= -0.25
>   /
> ATOMIC_SPECIES
>   Al  26.98  Al.vbc.UPF
> ATOMIC_POSITIONS
>   Al 0.00 0.00 0.00
> K_POINTS {automatic}
>    4 4 4 0 0 0
> 
>   = Al-1.ph_elph.in
>
=======================================================
> 
> phonons of Al
>   &inputph
>    tr2_ph=1.0d-14,
>    prefix='Al',
>    amass(1)=26.98,
>    fildyn='Al.dyn',
>    fildvscf='Al.dvscf',
>    filelph='Al-1.elph',
>    iverbosity = 1,
>    elph=.true.,
>    trans=.true.,
>   /
>   0.25  0.75 -0.25
> 
>   = Al-2.nscf.in
>
==========================================================
> 
>   &control
>      calculation='phonon',prefix  = 'Al'
>      pseudo_dir =
>
'/home/marini/Sources/espresso/espresso-3.0/pseudo/',
>   /
>   &system
>      ibrav=  2, celldm(1) =7.50, nat=  1, ntyp=
> 1,ecutwfc = 16, nbnd = 5,
>      occupations='smearing', smearing='mp',
> degauss=0.022
>   /
>   &electrons
>    diago_thr_init =  1.0d-6
>   /
>   &phonon
>      xqq(1)= 0.25  , xqq(2)= -0.25 , xqq(3)= 0.75
>   /
> ATOMIC_SPECIES
>   Al  26.98  Al.vbc.UPF
> ATOMIC_POSITIONS
>   Al 0.00 0.00 0.00
> K_POINTS {automatic}
>    4 4 4 0 0 0
> 
>   = Al-2.ph_elph.in
>
=======================================================
> 
> phonons of Al
>   &inputph
>    tr2_ph=1.0d-14,
>    prefix='Al',
>    amass(1)=26.98,
>    fildyn='Al.dyn',
>    fildvscf='Al.dvscf',
>    filelph='Al-2.elph',
>    iverbosity = 1,
>    elph=.true.,
>    trans=.true.,
>   /
>   0.25  -0.25 0.75
> 
> 
>
--------------------------------------------------------------------------
> 
=== message truncated ===


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