electron-phonon coupling for 2D materials

[ilias-serifi]

Hello everybody
i work on superconducting properties of an material 2D i run epw in order to have the electron phonon coupling and i found a huge lambda
lambda = 7456 meV

Best regards

[roxana]

Hi,

You can try to run the calculations for different k and q meshes and see if the problems persists.

Best,
Roxana

[hpaudya1]

Hi,

I have done some tests for a 2D material to calculate lambda using EPW v5.0 (QE-6.3). I also got unreasonable large value of lambda if I use "assume_isolated = '2D'" flag in QE-calculations. However, I got reasonable value of lambda without this flag. This time I can only guess for you that the source of the problem may be similar to mine. Although, the phonon are not different in both cases, basically EPW gives unreasonable large value of lambda.

If you are getting this data without using "assume_isolated = '2D'" flag, please let us know your inputs so that we can see in details.

Best,
Hari Paudyal

[ilias-serifi]

hello mr Hari Paudyal
i d'ont use this command on my calculations and i got got this unreasonable lambda value it's should be in the order of some meV and i got it in the order of eV this mean more than 1000 times more than the normal case
best regards

[ilias-serifi]

Hi guys
As you know bye the topic i get some unreasonable values of the linewidth and the spectral function of eliashberg and also the electron phonon coupling strength

i have many suspects before but now i get the phonon dispersion like the litterature and also the band structure
conserning the epw code i had the convergence in the spread of wannier functions so i have a good projections and all is alright nevertheless i still had a big measures normally the eliashberg spectral function dont exceed 1 or 2 meV and i get it around 1000 meV !!!


Best Rgards

[ilias-serifi]

Code: Select all

 Eliashberg Spectral Function in the Migdal Approximation
     ===================================================================

     lambda : 1757.8157878
     lambda_tr : 1946.0595019
 
     Estimated Allen-Dynes Tc
 
     logavg =    0.0000886 l_a2F = 1751.7988942
     mu =   0.10 Tc =         3.845000374466 K
     mu =   0.12 Tc =         3.788219159782 K
     mu =   0.14 Tc =         3.730767272617 K
     mu =   0.16 Tc =         3.672639590491 K
     mu =   0.18 Tc =         3.613831415621 K
     mu =   0.20 Tc =         3.554338527754 K
 omega    836.86172807561832    

[roxana]

Hi,

You need to provide more information about your system, including input/output files.

Best,
Roxana

[Zhe_L]

Hi,
I am confused by your description.
As far as I know, lambda is a dimensionless quantity. EPW outputs it with no unit too.
How can you get lambda = 7456 meV? Or you mean gamma = 7456 meV?
I also have more confusion about the dimensions of these quantities. Maybe I should post a new thread.
Best Regards

[ilias-serifi]

Hi
concerning the dimension of lambda is a dimensionless parameter which describe the enhancement of the band mass it should be around 0.5 and 2
for the Eliashberg spectral function is measured by meV like the frequency of phonon its shouldn't have more than 2 meV


For the professor Roxana i sent to you the whole of the input and the output files

Best Regards

[ilias-serifi]

Well i didn't arrive to send the input in private so i share it here
this is the input in order to have the linewidth and the eliashberg spectral function

Code: Select all

--
&inputepw
  prefix      = 'XX'
  amass(1)    = XXXXXXXXX
  outdir      = './'

  iverbosity  = 1
 ! ep_coupling = .true.
  elph        = .true.
  epbwrite    = .true.
  epbread     = .false.

  etf_mem     = 0

  epwwrite    = .true.
  epwread     = .false.

  nbndsub     =  8
  nbndskip    =  0

  wannierize  = .true.
  num_iter    = 300
  iprint      = 2
  dis_win_max = 30
  dis_froz_max= -1
  proj(1)     = 'Al:l=-3'   

  elecselfen  = .true.
! nest_fn     = .false.  
  phonselfen  = .true.
  a2f         = .true.

  specfun_el   = .false.
 ! wmin_specfun = -4
 ! wmax_specfun = 1
 ! nw_specfun   = 20

  parallel_k  = .true.
  parallel_q  = .false.

 !wdata(9) = 'kmesh_tol=0.00001'
  wdata(1) = 'bands_plot = .true.'
  wdata(2) = 'begin kpoint_path'
  wdata(3) = 'G 0.00 0.00 0.00 X 0.50 0.00 0.00'
  wdata(4) = 'X 0.50 0.00 0.00 S 0.50 0.50 0.00'
  wdata(5) = 'S 0.50 0.50 0.00 Y 0.00 0.50 0.00'
  wdata(6) = 'Y 0.00 0.50 0.00 G 0.00 0.00 0.00'
  wdata(7) = 'end kpoint_path'
  wdata(8) = 'bands_plot_format = gnuplot'
  wdata(9) = 'search_shells=40'
  wdata(10) = 'dis_num_iter= 20000'

  fsthick     = 15 ! eV 
  eptemp      = 0 ! K (same as PRB 76, 165108)
  degaussw    = 0.02 ! eV
   degaussq    = 0.05 ! eV
  dvscf_dir   = '../phonon/save/'
  filukk      = './Al.ukk'
  filkf       = 'Al_band.kpt'

! nkf1        = 6
! nkf2        = 6
! nkf3        = 6 

  nqf1        = 256
  nqf2        = 160
  nqf3        = 1
  
  nk1         = 32
  nk2         = 20
  nk3         = 1

  nq1         = 16
  nq2         = 10
  nq3         = 1
 /
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