Infinite value of Allen-dynes Tc, whichI believe leads to NAN in following calculations

Running EPW
1

Dear all,

I’m trying to find superconducting properties of PdCoO2 solving isotropic Eliashberg equations. I’ve been able to get correct band structure using wannierization and phonons with tag lifc=TRUE. But whenever I try to solve Eliashberg equations, I get very large values of Allen-dynes Tc, which leads to incorrect initial guess for gap. Please kindly suggest what could I possibly change or try in the following input
Below is my input & output for running epw

&inputepw
prefix = ‘PdCoO2’,
outdir = ‘./’
dvscf_dir = ‘../../phonon_444/save’
iverbosity = 3

ep_coupling = .true.
elph = .true.
epwwrite = .true.
epwread = .false.
lifc = .true.
wannierize = .true.
nbndsub = 10
efermi_read = .true.
fermi_energy = 14.5352


num_iter = 1000
dis_froz_min= 12
dis_froz_max= 17
proj(1) = ‘Pd:d’
proj(2) = ‘Co:d’



degaussw = 0.2 ! eV
degaussq = 0.5 ! meV
fsthick = 5 ! eV

ephwrite = .true.
eliashberg = .true.

liso = .true.
limag = .true.
lpade = .true.
lacon = .true.

nsiter = 500
npade = 40
conv_thr_iaxis = 1.0d-3
conv_thr_racon = 1.0d-3

wscut = 0.8 ! eV
muc = 0.1
nstemp = 10
temps = 0.25 10.25

mp_mesh_k = .true.
nkf1 = 24
nkf2 = 24
nkf3 = 24
nqf1 = 24
nqf2 = 24
nqf3 = 24
nk1 = 8
nk2 = 8
nk3 = 8
nq1 = 4
nq2 = 4
nq3 = 4
/

Output is attached.
Thanks!!

Best regards,
Prachi.

2

Hi Prachi,

I noticed;

“Electron-phonon coupling strength = 0.0845567”

which is very small, and Tc is zero

Best,
Hari

3

Hi Hari,

Thanks for your reply. Yes, the coupling constant is very small.
I’ve a small question, the output files have ‘*******’ in place of Tc. Does this mean its zero?
Because if I plug the numbers for coupling constant and w_log in the output file to find Tc, I got a very large number.

Thanks again.
Best regards,
Prachi.

4

Hi Prachi,

The Tc is printed as follows
https://gitlab.com/QEF/q-e/-/blob/develop/EPW/src/supercond.f90#L729

******* in your output file does not mean zero, but the way it is printed is not appropriate to print the very small value which is close to zero.

Best,
Hari

5

Hi Hari,

I see. Thanks a lot for the explanation.

Best regards,
Prachi.