I am trying to find superconducting critical temperature of a 2D material.

When I try to do epw.x calculations, I met the following error:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Error in routine mix_broyden (1):

factorization

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

and also getting NaN in Pade approximant of isotropic Eliashberg equations from imaginary-axis to real-axis.

I am getting this same error, even if I have changed broyden_beta parameter from its default value (0.7) to some lower value (0.4).

I am attaching epw1.in file

Code: Select all

```
--
&inputepw
amass(1) = 18.9984032
amass(2) = 183.84
outdir = './'
dvscf_dir = '../phono/save'
ep_coupling = .true.
elph = .true.
epwwrite = .true.
epwread = .false.
wannierize = .true.
nbndsub = 21
bands_skipped = 'exclude_bands = 1-19'
broyden_beta = 0.4
num_iter = 500
dis_froz_min= 0
dis_froz_max= 4.789
proj(1) = 'random'
proj(2) = 'W:dz2;dx2-y2;dxy'
wdata(1) = 'bands_plot = .true.'
wdata(2) = 'begin kpoint_path'
wdata(3) = 'G 0.00 0.00 0.00 M 0.50 0.00 0.00'
wdata(4) = 'M 0.50 0.00 0.00 K 0.33 0.33 0.00'
wdata(5) = 'K 0.33 0.33 0.00 G 0.00 0.00 0.00'
wdata(6) = 'end kpoint_path'
wdata(7) = 'bands_plot_format = gnuplot'
wdata(8) ='dis_num_iter= 1000'
wdata(9) = 'guiding_centres = .true.'
iverbosity = 2
fsthick = 0.2127773616744 ! eV
degaussw = 0.05 ! eV
degaussq = 1.0 ! 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 = 1.0 ! eV
muc = 0.1
temps = 0.2 0.25 0.3 0.35 0.4
nk1 = 24
nk2 = 24
nk3 = 1
nq1 = 4
nq2 = 4
nq3 = 1
mp_mesh_k = .true.
nkf1 = 240
nkf2 = 240
nkf3 = 1
nqf1 = 40
nqf2 = 40
nqf3 = 1
/
```

Code: Select all

```
===================================================================
Solve isotropic Eliashberg equations
===================================================================
Finish reading freq file
Fermi level (eV) = 1.7453510248E+00
DOS(states/spin/eV/Unit Cell) = 8.9771142336E-01
Electron smearing (eV) = 5.0000000000E-02
Fermi window (eV) = 2.1277736167E-01
Nr irreducible k-points within the Fermi shell = 1465 out of 4921
1 bands within the Fermi window
Finish reading egnv file
Max nr of q-points = 486
Finish reading ikmap files
Start reading .ephmat files
Finish reading .ephmat files
Finish reading a2f file
Electron-phonon coupling strength = 0.7134824
Estimated Allen-Dynes Tc = 4.589131 K for muc = 0.10000
Estimated w_log in Allen-Dynes Tc = 10.860257 meV
Estimated BCS superconducting gap = 0.696011 meV
temp( 1) = 0.20000 K
Solve isotropic Eliashberg equations on imaginary-axis
Total number of frequency points nsiw( 1) = 9235
Cutoff frequency wscut = 1.0001
iter ethr znormi deltai [meV]
1 2.415921E+00 1.687911E+00 6.944699E-01
2 4.064958E-01 1.688261E+00 7.356576E-01
3 5.782194E-01 1.687632E+00 7.937560E-01
4 2.763219E-02 1.685545E+00 8.406962E-01
5 2.492487E-02 1.684678E+00 8.618104E-01
6 7.936021E-02 1.681698E+00 9.338961E-01
7 6.955777E-03 1.681563E+00 9.378374E-01
8 1.375038E-02 1.681015E+00 9.511524E-01
9 5.473966E-03 1.681234E+00 9.458635E-01
10 1.355704E-05 1.681234E+00 9.458767E-01
Convergence was reached in nsiter = 10
iaxis_imag : 1.31s CPU 1.38s WALL ( 1 calls)
Pade approximant of isotropic Eliashberg equations from imaginary-axis to real-axis
Cutoff frequency wscut = 1.0000
pade Re[znorm] Re[delta] [meV]
3694 NaN NaN
Convergence was reached for N = 3694 Pade approximants
raxis_pade : 0.57s CPU 0.70s WALL ( 1 calls)
Analytic continuation of isotropic Eliashberg equations from imaginary-axis to real-axis
Total number of frequency points nsw = 8500
Cutoff frequency wscut = 1.0000
iter ethr Re[znorm] Re[delta] [meV]
1 NaN NaN NaN
2 NaN NaN NaN
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Error in routine mix_broyden (1):
factorization
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
stopping ...
```

Thank you.

Regards

Sahil Dani

Research Scholar

IIT Ropar, INDIA.