EPW Forum

Dear all,

I am trying to calculate the phonon linewidth for 2D materials as given in FCC lead tutorial. Here I puzzled with the sudden exit of calculations (without any error or warning) after Phonon Self-Energy in the Migdal Approximation of all q-points. Kindly see my input and out put and suggest me for further calculations
PS: I successfully finished my calculations for electron-phonon coupling strangth and Tc values for the same 2D material and my Tc also compare well with experiments (For this, I followed MgB2 tutorials)

epw.in
--
&inputepw
prefix = 'NbSe2',
amass(1) = 92.91,
amass(2) = 78.96,
outdir = './'

elph = .true.
kmaps = .false.
epbwrite = .true.
epbread = .false.

epwwrite = .true.
epwread = .false.


nbndsub = 17
efermi_read = .true.
fermi_energy= -1.7757
wannierize = .true.
num_iter = 500
dis_win_min = -7.0
dis_froz_min = -7.0
dis_froz_max= -1.7
dis_win_max = 22.0

proj(1) = 'Nb:l=0;l=1;l=2'
proj(2) = 'Se:l=0;l=1'
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 = xmgr'
wdata(8) = 'guiding_centres = TRUE '

iverbosity = 0

elinterp = .true.
phinterp = .true.

tshuffle2 = .true.
tphases = .false.

elecselfen = .false.
phonselfen = .true.

parallel_k = .true.
parallel_q = .false.

fsthick = 1! eV
eptemp = 300 ! K
degaussw = 0.05 ! eV

a2f = .true.

dvscf_dir = '../phonons/save'


nkf1 = 32
nkf2 = 32
nkf3 = 1

nqf1 = 32
nqf2 = 32
nqf3 = 1

nk1 = 8
nk2 = 8
nk3 = 1

nq1 = 8
nq2 = 8
nq3 = 1

/
10 cartesian
0.000000000 0.000000000 0.000000000 1.000000000
0.073128834 0.126662856 0.000000000 1.000000000
0.146257668 0.253325712 0.000000000 1.000000000
0.219386502 0.379988568 0.000000000 1.000000000
-0.292515336 -0.506651424 0.000000000 1.000000000
0.219386502 0.126662856 0.000000000 1.000000000
0.292515336 0.253325712 0.000000000 1.000000000
0.365644170 0.379988568 0.000000000 1.000000000
0.438773004 0.253325712 0.000000000 1.000000000
0.511901838 0.379988568 0.000000000 1.000000000

epw.out

Number of (k,k+q) pairs on the Fermi surface: 1024 out of 1024


ismear = 1 iq = 1024 coord.: 0.96875 0.96875 0.00000 wt: 0.00098
-------------------------------------------------------------------
lambda( 1 )= 0.000000 gamma= 0.000000 meV omega= 0.5255 meV
lambda( 2 )= 0.241519 gamma= 0.003919 meV omega= 2.0481 meV
lambda( 3 )= 0.220894 gamma= 0.010888 meV omega= 3.5695 meV
lambda( 4 )= 0.000000 gamma= 0.000000 meV omega= 16.4505 meV
lambda( 5 )= 0.000000 gamma= 0.000000 meV omega= 16.6060 meV
lambda( 6 )= 0.080659 gamma= 0.235116 meV omega= 27.4497 meV
lambda( 7 )= 0.058111 gamma= 0.194748 meV omega= 29.4327 meV
lambda( 8 )= 0.073774 gamma= 0.255529 meV omega= 29.9221 meV
lambda( 9 )= 0.000000 gamma= 0.000000 meV omega= 36.6696 meV
lambda( tot )= 0.674957
-------------------------------------------------------------------


Number of (k,k+q) pairs on the Fermi surface: 1024 out of 1024


===================================================================================
= BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES
= PID 43477 RUNNING AT saint
= EXIT CODE: 62
= CLEANING UP REMAINING PROCESSES
= YOU CAN IGNORE THE BELOW CLEANUP MESSAGES
===================================================================================

Sincerely
Samudrala Appalakondaiah

Hello,

This error should be linked with the bug of your other post with PGI.

Best,

Samuel

Dear Samuel,

Thank you for the modification. Now, The calculations are running successfully but the results seems something unphysical. Please see the below values for lambda_max and electron-phonon coupling strengths (which is around 10). Kindly see my input and give me any modifications

Finish reading .ephmat files

lambda_max = 5189.3956183 lambda_k_max = 27.5206526

Electron-phonon coupling strength = 10.4879916

Estimated Allen-Dynes Tc = 2.5203523 K for muc = 0.16000

Estimated BCS superconducting gap = 0.0003822 eV

WARNING WARNING WARNING

The code will crash for tempsmax much larger than Allen-Dynes Tc

temp( 1) = 2.0000 K

epw.in
--
&inputepw
prefix = 'NbSe2',
amass(1) = 92.91,
amass(2) = 78.96,
outdir = './'

ep_coupling = .true.
elph = .true.
kmaps = .false.
epbwrite = .true.
epbread = .false.

epwwrite = .true.
epwread = .false.

etf_mem = .true.

nbndsub = 17
efermi_read = .true.
fermi_energy= -1.7854
wannierize = .true.
num_iter = 500
dis_win_min = -3.0
dis_froz_min = -3.0
dis_froz_max= -1.76
dis_win_max = 6.0

proj(1) = 'Nb:l=0;l=1;l=2'
proj(2) = 'Se:l=0;l=1'
wdata(1) = 'guiding_centres = TRUE '

iverbosity = 2

elinterp = .true.
phinterp = .true.

tshuffle2 = .true.
tphases = .false.

parallel_k = .true.
parallel_q = .false.

eps_acustic = 2.0 ! Lowest boundary for the
ephwrite = .true. ! Writes .ephmat files used when wliasberg = .true.

fsthick = 2.0 ! eV
eptemp = 300 ! K
degaussw = 0.20 ! eV
nsmear = 1
delta_smear = 0.04 ! eV

degaussq = 0.5 ! meV
nqstep = 500

eliashberg = .true.

laniso = .true.
limag = .true.
lpade = .true.

conv_thr_iaxis = 1.0d-4

wscut = 1.0 ! eV Upper limit over frequency integration/summation in the Elisashberg eq

nstemp = 1
tempsmin = 2.00
tempsmax = 5.00

nsiter = 500

muc = 0.16

dvscf_dir = '../phonons/save'


nkf1 = 32
nkf2 = 32
nkf3 = 1

nqf1 = 32
nqf2 = 32
nqf3 = 1

nk1 = 16
nk2 = 16
nk3 = 1

nq1 = 16
nq2 = 16
nq3 = 1

/
30 cartesian
0.000000000 0.000000000 0.000000000 1.000000000
0.036542907 0.063294172 0.000000000 1.000000000
0.073085815 0.126588344 0.000000000 1.000000000
0.109628722 0.189882516 0.000000000 1.000000000
0.146171629 0.253176688 0.000000000 1.000000000
0.182714536 0.316470860 0.000000000 1.000000000
0.219257444 0.379765032 0.000000000 1.000000000
0.255800351 0.443059204 0.000000000 1.000000000
-0.292343258 -0.506353376 0.000000000 1.000000000
0.109628722 0.063294172 0.000000000 1.000000000
0.146171629 0.126588344 0.000000000 1.000000000
0.182714536 0.189882516 0.000000000 1.000000000
0.219257444 0.253176688 0.000000000 1.000000000
0.255800351 0.316470860 0.000000000 1.000000000
0.292343258 0.379765032 0.000000000 1.000000000
0.328886165 0.443059204 0.000000000 1.000000000
0.219257444 0.126588344 0.000000000 1.000000000
0.255800351 0.189882516 0.000000000 1.000000000
0.292343258 0.253176688 0.000000000 1.000000000
0.328886165 0.316470860 0.000000000 1.000000000
0.365429073 0.379765032 0.000000000 1.000000000
0.401971980 0.443059204 0.000000000 1.000000000
0.328886165 0.189882516 0.000000000 1.000000000
0.365429073 0.253176688 0.000000000 1.000000000
0.401971980 0.316470860 0.000000000 1.000000000
0.438514887 0.379765032 0.000000000 1.000000000
0.438514887 0.253176688 0.000000000 1.000000000
0.475057794 0.316470860 0.000000000 1.000000000
0.511600702 0.379765032 0.000000000 1.000000000
0.548143609 0.316470860 0.000000000 1.000000000

Dear appalakondaiah,

2D materials requires special care.
The strong Frohlich interaction is likely to produce spurious interaction between the 2D materials and its replica.
I assume that you need to truncate the Coulomb interaction to solve this issue.

See for example PRB 94, 085415 (2016).

Unfortunately, this is not yet coded into EPW.

Best,

Samuel

Dear appalakondaiah,

Besides the issues Samuel has mentioned you should also check the following points:

1) decay of Hamiltonian, dynamical matrix, and electron-phonon matrix elements in the Wannier representation (see as an example Fig. 2 for Pb in Computer Physics Communications 181 (2010) 21402148).

2) convergence of e-ph coupling with respect to the fine k- and q-meshes. The e-ph coupling converges faster for random meshes (see the example for Pb). If you want to solve the Migdal-Eliashberg equations than you will be constrained to use uniform meshes but you can set mp_mesh_k=.true. to speed up the calculations (see the example for MgB2).

Best,
Roxana

Dear Prof. Samuel and Prof. Roxana Margine

Thank you for the replies. I will try with the suggestions and get back you again..

with regards
S. Appalakondaiah