## Diamond example - phonon linewidths - factor discrepancy

Post here questions linked with issue while running the EPW code

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NFH
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### Diamond example - phonon linewidths - factor discrepancy

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.

epwwrite    = .true.

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

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.

- 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