Diamond example - phonon linewidths - factor discrepancy

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NFH
Posts: 13
Joined: Fri Jan 29, 2016 12:43 pm
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Diamond example - phonon linewidths - factor discrepancy

Post by NFH »

Dear all,

we're currently dealing with the physics of phonon instabilities in doped semiconductors
and a student of mine calculated the phonon linewidths for these systems. Even carefully converged with respect to k/q-meshes and smearing the line widths appeared too large for me (up to 50-100meV for sc with 1-3x10^19cm-3 rigid band doping).

So I went back to the examples to get some ideas. I took the doped-Carbon example straight out of the folder and tried the calculations for the phonon self-energy of doped Carbon (Example 1):

Code: Select all

&inputepw
  prefix      = 'diam'
  amass(1)    = 12.01078
  outdir      = './'

  iverbosity  = 0

  elph        = .true.
  epbwrite    = .true.
  epbread     = .false.

  epwwrite    = .true.
  epwread     = .false.

  nbndsub     =  4

  wannierize  = .true.
  num_iter    = 300
  iprint      = 2
  dis_win_max = 12
  dis_froz_max= 7
  proj(1)     = 'f=0,0,0:l=-3'   

  elecselfen  = .false.
  phonselfen  = .true.
  a2f         = .false.


  fsthick     = 1.36056981 ! eV 
  temps       = 300 ! K (same as PRB 76, 165108)
  degaussw    = 0.1 ! eV

  dvscf_dir   = '../phonons/save'
  filukk      = './diam.ukk'
  filqf       = 'meshes/path.dat'
  
  nkf1        = 50
  nkf2        = 50
  nkf3        = 50
  
  nk1         = 6
  nk2         = 6
  nk3         = 6

  nq1         = 6
  nq2         = 6
  nq3         = 6
 /
My linewidths looked good
Image

but seem a factor of 2 too large compared to Fig4 in https://docs.epw-code.org/doc/B-doped-diamond.html, which should be the same as I used a homogeneous and unshifted k-grid with 50x50x50 points at 100meV smearing.
Image

- So were does this factor of 2 stems from? The linewidth in the EPW output is defined as twice the phonon self energy, right?

- Moreover why is in this calculation the Fermi energy not fixed in the conduction bands like for the electron self energy calculations? That should matter for the phonon-SE, too, right?

thanks for any hints,
Nicki

MLU/MPI Halle

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