EPW Forum

Dear,

I am still having problems calculating the superconducting gap and Tc using The Eliashberg formalism. From the McMillan Dynes formula , I expect the superconducting temperature to be ~2.9K which was estimated using EPW. I have run the isotropic Eliashberg calculation for temps(1)=0.9 and increased it to 1.1K , which are not very small temperatures or temperatures close to Tc, but I am still getting an error:

Finish reading a2f file

Electron-phonon coupling strength = 0.0000000

Estimated Allen-Dynes Tc = NaN K for muc = 0.10000

Estimated w_log in Allen-Dynes Tc = NaN meV

Estimated BCS superconducting gap = NaN meV

temp( 1) = 1.10000 K

Solve isotropic Eliashberg equations on imaginary-axis

Total number of frequency points nsiw( 1) = 1679
Cutoff frequency wscut = 1.0003

iter ethr znormi deltai [meV]
1 NaN NaN NaN
2 NaN NaN NaN
3 NaN NaN NaN
4 NaN NaN NaN

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Error in routine mix_broyden (1):
factorization
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Any help is appreciated. the input file is :


outdir='/',
dvscf_dir ='/'

elph = .true.
kmaps = .false.
epbwrite = .true.
epbread = .false.
epwwrite = .true.
epwread = .false.
ephwrite=.true.
wannierize=.true.
nbndsub=14
num_iter=500
bands_skipped='exclude_bands=1,2,17,40'
max_memlt=5
!dis_froz_min = -10.0d0
!dis_froz_max = 0.0d0
proj(1)=''
proj(2)=''
proj(3)=''
proj(4) =''
system_2d=.true.
wscut=1.0
efermi_read=.true.
fermi_energy= -1.5629

etf_mem=1

wdata(1) ='search_shells=30'
wdata(2) ='bands_plot =.true.'
wdata(3) ='begin kpoint_path'
wdata(4)='G 0.000000 0.000000 0.000000 K 0.3333333 0.3333333 0.0000000'
wdata(5)='K 0.3333333 0.3333333 0.000000 M 0.5000000 0.0000000 0.0000000'
wdata(6)='M 0.5000000 0.0000000 0.000000 G 0.000000 0.000000 0.0000000'
wdata(7)='end kpoint_path'

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

eliashberg=.true.
liso=.true.
limag=.true.
lpade=.true.
muc=0.1
nsiter=4000
temps(1)=1.1
temps(2)=1.3
temps(3)=1.6
temps(4)=1.9
temps(5)=2.2
temps(6)=2.5
temps(7)=2.8
fsthick = 7 ! eV
degaussw = 0.005 ! eV
iverbosity=0

mp_mesh_k=.true.

nkf1 = 50
nkf2 = 50
nkf3 = 1

nqf1 = 50
nqf2 = 50
nqf3 = 1


nk1 = 36
nk2 = 36
nk3 = 1

nq1 = 12
nq2 = 12
nq3 = 1
/
74 cartesian

Regards

Hi,

I just noticed that the e-ph coupling strength in your output file is zero. It appears that something went wrong when reading a2f file. So check that the is correct.

"Electron-phonon coupling strength = 0.0000000"

Best,
Roxana

Dear eliephys78:

Could you let me know the total number of bands for the disentanglement for Wannierization in your calculation?
The excluded bands should consist of one or two contiguous blocks of bands (lowest or highest).
If you want to exclude the band groups composed of 1-2 bands and 17-40 bands, you should use the following input:
Lastly, I think that 2D treatment is currently not supported.
Sincerely,

H. Lee

Dear Drs. Lee and Roxana,

Thanks for your messages.

Dr. Roxana, i will check that.

Dr. Lee, indeed the exclude bands flag should have been 1,2,17-40. Regarding the system_2d flag, I have been using it to compute EPW for some 2D structures I am working on.. I haven't got any errors. So I thought there was no problem with that.

I will correct the potential errors and see if this works. Once again, many thanks

Regards

Dear eliephys78:

Regarding the 2D treatment in EPW:
I think that you already checked it, but if it is not the case, please check the post at viewtopic.php?f=3&t=1311 .

Sincerely,

H. Lee

Dear Dr. Lee,

Thanks for your message. I have checked this post last year. However what got me confused is the flag system_2d=.true. in the input (Documentation)

"system_2d

Default

.false.

Description

If .true. the system is two-dimensional (vaccum is in z-direction) and the k and q meshes are defined in the xy-plane."

which kind of gave me the wrong impression that EPW does work for 2D and one does not have to sample along the z-direction.

Regards