inconsistent electron-phonon coupling strength

[jiachen]

Dear All,

I have obtained different electron-phonon coupling strength from spectral function and files for solving Eliashberg equation. I copy a part of output file in following. As you can see, lambda from spectral function is 1.73, but after writing and reading .freq, .egnv, .ikmap and .ephmat files, it changed to 2.02. I wonder what caused this, and how can I fix this? Appreciate your help.

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

lambda : 1.7285861
lambda_tr : 1.7374491

Estimated Allen-Dynes Tc

logavg = 0.0007125 l_a2F = 1.7210705
mu = 0.10 Tc = 14.466465134752 K
mu = 0.12 Tc = 13.727301202059 K
mu = 0.14 Tc = 12.986510401578 K
mu = 0.16 Tc = 12.245231413771 K
mu = 0.18 Tc = 11.504745732233 K
mu = 0.20 Tc = 10.766490635967 K
a2F : 29.70s CPU 29.89s WALL ( 1 calls)
===================================================================
Solve anisotropic Eliashberg equations ===================================================================

Fermi level (eV) = 1.1189500000E+01
DOS(states/spin/eV/Unit Cell) = 5.5556743777E+00
Electron smearing (eV) = 2.0000000000E-02
Fermi window (eV) = 1.0000000000E-01
Nr k-points within the Fermi shell = 3080 out of 4096
2 bands within the Fermi window
Finish reading .egnv file
Finish reading .freq file Max nr of q-points = 3080
Finish reading .ikmap files
Start reading .ephmat files
Finish reading .ephmat files
lambda_max = 29.4605785 lambda_k_max = 2.6884743
Electron-phonon coupling strength = 2.0264060
Estimated Allen-Dynes Tc = 14.1305698 K for muc = 0.16000
Estimated BCS superconducting gap = 0.0021431 eV

[roxana]

Hi,

You will need to provide more information about your system. For example, did you use uniform meshes for both calculations and the same Fermi window?

Best,
Roxana

[jiachen]

Dear Roxana,

Thank you for response. I copy the input file in following. The output is from one continuous calculation with one input file, so I guess all input parameters have to be consistent, right? Again, really appreciate your help.

----------------------
&inputepw
prefix = 'pbmos'
amass(1) = 96
amass(2) = 32
amass(3) = 207.2
outdir = './'

iverbosity = 2

elph = .true.
ep_coupling = .true.
epbwrite = .false.
epbread = .true.
epwwrite = .true.
epwread = .false.
ephwrite = .true.
kmaps = .true.
nbndsub = 9
nbndskip = 60

! efermi_read = .true.
! fermi_energy= 11.189

etf_mem = .true.
lpolar = .true.
max_memlt = 1.6

wannierize = .true.
num_iter = 2000
iprint = 2
dis_froz_min = 9.70
dis_froz_max = 11.50

proj(1) = 'random'

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

parallel_k = .true.
parallel_q = .false.

fsthick = 0.1 ! eV
eptemp = 300
degaussw = 0.01 ! eV

eliashberg = .true.
laniso = .true.
limag = .true.
lpade = .false.
conv_thr_iaxis = 1.0d-4
wscut = 1.0 ! eV

nstemp = 1
tempsmin = 1.00
tempsmax = 20.00
nswi = 20
nsiter = 100
muc = 0.16


dvscf_dir = '../14q_phon/save'
filukk = './pbmos.ukk'
! filqf = 'meshes/path.dat'

wdata(1) = 'kmesh_tol=0.0000001'

nkf1 = 20
nkf2 = 20
nkf3 = 20

nqf1 = 20
nqf2 = 20
nqf3 = 20

nk1 = 6
nk2 = 6
nk3 = 6

nq1 = 3
nq2 = 3
nq3 = 3
/
14 cartesian
0.000000000000000E+00 0.000000000000000E+00 0.000000000000000E+00 0.03703705
-0.108361369393588E-04 0.411309741978692E-03 0.333269214297111E+00 0.07407405
-0.434190800650392E-03 0.333220201833956E+00 -0.551696871058361E-02 0.07407405
-0.445026937589751E-03 0.333631511575935E+00 0.327752245586527E+00 0.07407405
-0.423354663711034E-03 0.332808892091978E+00 -0.338786183007694E+00 0.07407405
0.333198334414189E+00 -0.468808674947273E-02 -0.506297106874096E-02 0.07407405
0.333187498277250E+00 -0.427677700749404E-02 0.328206243228370E+00 0.07407405
0.333209170551129E+00 -0.509939649145142E-02 -0.338332185365852E+00 0.07407405
0.332764143613539E+00 0.328532115084484E+00 -0.105799397793246E-01 0.07407405
0.332753307476600E+00 0.328943424826462E+00 0.322689274517786E+00 0.07407405
0.332774979750478E+00 0.328120805342505E+00 -0.343849154076435E+00 0.07407405
0.333632525214840E+00 -0.337908288583429E+00 0.453997641842654E-03 0.07407405
0.333621689077900E+00 -0.337496978841450E+00 0.333723211938953E+00 0.07407405
0.333643361351779E+00 -0.338319598325408E+00 -0.332815216655268E+00 0.07407405

[roxana]

Hi,

If you run the calculation with the flag delta_approx=.true. you should get the same result. This way the calculation of Eliashberg spectral function using the phonon self-energy (phonselfen = .true. and a2f = .true.) will be done in the same way as using (eliashberg=.true.).

Best,
Roxana

[jiachen]

Dear Roxana,

I did test with delta_approx=.true. You are right. Thank you!