Many zero scattering rate values for bulk Ge and Si

[Vahid]

Dear EPW Users,

My test runs on Si and Ge ended but I have many zero scattering rates above 2eV. The rest of the scattering rates agrees with the literature. I am not sure if this is installation, QE or EPW related. Has anyone seen this behavior and is there a way to deal with these zeros? Here is my epw.in (nbnd=12):

Code: Select all

--
&inputepw
  prefix      = 'ge'
  amass(1)    = 72.63
  outdir      = './'

  iverbosity  = 0

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

  epwwrite    =  .true.
  epwread     =  .false.

  !efermi_read = .true. 
  !fermi_energy = 6.532757 

  nbndsub     =  8
  nbndskip    =  0

  wannierize  = .true.
  num_iter    = 300
  iprint      = 2
  dis_win_max = 17
  dis_froz_max= 6
  proj(1)     = 'Ge:sp3'   

  elinterp    = .true.
  phinterp    = .true.

  tshuffle2   = .true.
  tphases     = .false.

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

  parallel_k  = .true.
  parallel_q  = .false.

  fsthick     = 2 ! eV 
  eptemp      = 300 ! K 
  degaussw    = 0.03 ! eV

  dvscf_dir   = '../phonons/save'
  filukk      = './ge.ukk'

  nkf1        = 20
  nkf2        = 20
  nkf3        = 20

  nqf1        = 40
  nqf2        = 40
  nqf3        = 40
  
  nk1         = 6
  nk2         = 6
  nk3         = 6

  nq1         = 6
  nq2         = 6
  nq3         = 6
 /
       16 cartesian
   0.0000000   0.0000000   0.0000000  0.0092593
  -0.1666667   0.1666667  -0.1666667  0.0740741
  -0.3333333   0.3333333  -0.3333333  0.0740741
   0.5000000  -0.5000000   0.5000000  0.0370370
   0.0000000   0.3333333   0.0000000  0.0555556
  -0.1666667   0.5000000  -0.1666667  0.2222222
   0.6666667  -0.3333333   0.6666667  0.2222222
   0.5000000  -0.1666667   0.5000000  0.2222222
   0.3333333   0.0000000   0.3333333  0.1111111
   0.0000000   0.6666667   0.0000000  0.0555556
   0.8333333  -0.1666667   0.8333333  0.2222222
   0.6666667   0.0000000   0.6666667  0.1111111
   0.0000000  -1.0000000   0.0000000  0.0277778
   0.6666667  -0.3333333   1.0000000  0.2222222
   0.5000000  -0.1666667   0.8333333  0.2222222
  -0.3333333  -1.0000000   0.0000000  0.1111111

Thank you,
Vahid

Vahid Askarpour
Department of Physics and Atmospheric Science
Dalhousie University,
Halifax, NS Canada

[sponce]

Dear Vahid,

This is because you have specified

Code: Select all

fsthick = 2 ! eV 

in your input file.

Could you format your posts using the "code" balist please.

Best,

Samuel

[Vahid]

Dear Samuel,

Your suggestion worked and the zeros disappeared. I apologize for not having used the code format. I will do so in the future.

Thank you and best wishes,

Vahid

[amosyang]

Dear Samuel,

What's the detailed meaning of fsthick? Does it means that the electron-phonon interaction within the fermi surface should be zero, or what else?
In the calculation, what rules we should follow to set the value of fsthick?

Best

Jiayue
RWTH Aachen University, Germany

[sponce]

Dear Jiayue,

Its just an energy window around the Fermi level where the calculations are performed.

For properties liked with the imaginary part of the self-energy, you have dirac deltas in the formulas. Therefore the influence of far away (in energy) bands on the bands you are interested with, is small.

This fstihick variables is just there to speed-up the calculations.

Increasing fsthick should not modify your results. If it does, then it means your fstick is too small.

If you do not want to check this and do not care about computational cost too much, you can set fsthick to a large value like 20 eV.

Best,

Samuel

[amosyang]

Dear Samuel,

In some situations, I have to increase the value of fsthick. For example, the doping will shift the Fermi level upwards or downwards. If the fsthick is too small, I will get the zero lamda.

Best

Jiayue

[Danansmith]

Excellent post! Thanks again for posting this here.



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