How to select degaussw ?

[liu xinbao]

Dear all,

I am trying to calculate the electron-phonon coupling in TiSe_2 and I got the following result.

Then I'm confused about how to select correct the smearing parameter of delta function which is controlled by the tag degaussw.
I found two similar graph in the literature https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.024505


I have review some discussion about this parameter, I thought that if we increase k-mesh or q-mesh, the lambda will converge to an constant.
But in my case and the PRB case, the lambda just increase when sigma close to 0 even when we increase k&q mesh.
Why we can select 15meV or 35meV as the convergence criterion value?
Hope for any discussion about this.

Bests,
Xinbao,

[ilias-serifi]

HI
i have the same problem for the electron phonon coupling for an 2D metal
i got unreasonable electron phonon coupling and eliashberg spectral function for a q and k meshes 320*200*1 and 320*200*1
i had lambda = 290

Code: Select all

&inputepw
  prefix      = 'xx'
  amass(1)    = xxxxxxxxxx
  outdir      = './'

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

!  etf_mem     = 0

  epwwrite    = .true.
  epwread     = .false.

  nbndsub     =  8
  nbndskip    =  0

  wannierize  = .true.
  num_iter    = 150
  iprint      = 2
  dis_win_max = 20
  dis_froz_max= -1
  proj(1)     = 'xx:l=-3'   

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

 ! specfun_el   = .true.
  wmin_specfun = 0
  wmax_specfun = 0.001
  nw_specfun   = 50

 ! 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      = 0.075 ! K (same as PRB 76, 165108)
  degaussw    = 0.025 ! eV
  degaussq    = 0.5 ! meV
  dvscf_dir   = '../phonon/save/'
  filukk      = './xx.ukk'
!  filkf       = 'xx_band.kpt'
 ! filqf = 'kpath.dat'




 nkf1        = 320
 nkf2        = 200
 nkf3        = 1

  nqf1        = 320
  nqf2        = 200
  nqf3        = 1
  
  nk1         = 32
  nk2         = 20
  nk3         = 1

  nq1         = 16
  nq2         = 10
  nq3         = 1
 /
      54 cartesian
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