EPW Forum

Dear all,

I hope you are doing well. I want to clarify one issue regarding EPW calculation for electron-phonon coupling (|g|).

Case (I): When I run the epw.in with Eliashberg = .true. I'm getting |g| and Tc. This is |g| is different from my case II, where I am running epw.in with Eliashberg = .false. So my question is why |g| values are different in both cases? In both cases, I am giving prtgkk = .true. How Eliashberg = .true./.false. handling and printing |g| in epw.out?

Case (II): When I run the epw.in with Eliashberg = .false.

The related input files are given below for case I:

scf.in:
&CONTROL
calculation = 'scf'
prefix = 'li_30GPa'
outdir = './tmp/'
etot_conv_thr = 1.0000000000d-05
forc_conv_thr = 1.0000000000d-04
pseudo_dir = '../pseudo/'
tstress = .true.
tprnfor = .true.
verbosity = 'high'
/
&SYSTEM
ibrav = 0
nat = 1
nosym = .false.
ntyp = 1
ecutwfc = 100
occupations = 'smearing'
smearing = 'mv'
degauss = 0.05
/
&ELECTRONS
conv_thr = 2.0000000000d-10
electron_maxstep = 200
mixing_beta = 7.0000000000d-01
/
&IONS
/
&CELL
press_conv_thr = 0.01
/
ATOMIC_SPECIES
Li 6.941 Li.upf

CELL_PARAMETERS (angstrom)
0.000000000 1.699673798 1.699673798
1.699673798 0.000000000 1.699673798
1.699673798 1.699673798 0.000000000

ATOMIC_POSITIONS (crystal)
Li 0.0000000000 0.0000000000 0.0000000000

K_POINTS automatic
24 24 24 0 0 0

nscf.in (truncated):

&CONTROL
calculation = 'nscf'
prefix = 'li_30GPa'
outdir = './tmp/'
etot_conv_thr = 1.0000000000d-05
forc_conv_thr = 1.0000000000d-04
pseudo_dir = '../pseudo/'
tstress = .true.
tprnfor = .true.
verbosity = 'high'
/
&SYSTEM
ibrav = 0
nat = 1
nosym = .false.
ntyp = 1
nbnd = 6
ecutwfc = 100
occupations = 'smearing'
smearing = 'mv'
degauss = 0.05
/
&ELECTRONS
conv_thr = 2.0000000000d-10
electron_maxstep = 200
mixing_beta = 7.0000000000d-01
/
&IONS
/
&CELL
press_conv_thr = 0.01
/
ATOMIC_SPECIES
Li 6.941 Li.upf

CELL_PARAMETERS (angstrom)
0.000000000 1.699673798 1.699673798
1.699673798 0.000000000 1.699673798
1.699673798 1.699673798 0.000000000

ATOMIC_POSITIONS (crystal)
Li 0.0000000000 0.0000000000 0.0000000000
K_POINTS crystal
4096
0.00000000 0.00000000 0.00000000 2.441406e-04
0.00000000 0.00000000 0.06250000 2.441406e-04
0.00000000 0.00000000 0.12500000 2.441406e-04

ph.in:

&inputph
verbosity='high'
prefix = 'li_30GPa',
outdir = './tmp/',
fildyn = 'li_30GPa.dyn.xml',
ldisp=.true.
epsil=.false.
lqdir=.true.
fildvscf = 'dvscf',
tr2_ph = 1.0d-14,
nq1 = 8, nq2 = 8, nq3 = 8
/

and epw.in
&inputepw
prefix = 'li_30GPa',
amass(1) = 6.941,
outdir = './tmp'
dvscf_dir = '/home/numan/li_epw_q-e7.5/phonon_lda_30GPa_8x8x8/save'
ep_coupling = .true. ! run e-ph coupling calculation
elph = .true. ! calculate e-ph coefficients
epwwrite = .true. ! write e-ph matrices in Wann representation
epwread = .false. ! read e-ph matrices from 'prefix.epmatwp' file
wannierize = .true.
nbndsub = 1
bands_skipped = 'exclude_bands = 1, 3-6'
!efermi_read = .true.
!fermi_energy = 3.9092
num_iter = 300
dis_win_min = -0.0273
dis_win_max = 9.1842
dis_froz_min = -0.0265
dis_froz_max = 9.0000
proj(1) = 'Li:s'
wannier_plot= .true.
wdata(1) = 'bands_plot = .true.'
wdata(2) = 'dis_num_iter = 1000'
wdata(3) = 'dis_conv_tol = 1E-11'
wdata(4) = 'conv_tol = 1E-11'
wdata(5) = 'begin kpoint_path'
wdata(6) = 'G 0.000 0.000 0.000 L 0.500 0.500 0.500'
wdata(7) = 'L 0.500 0.500 0.500 W 0.500 0.250 0.750'
wdata(8) = 'W 0.500 0.250 0.750 X 0.500 0.000 0.500'
wdata(9) = 'X 0.500 0.000 0.500 G 0.000 0.000 0.000'
wdata(10) = 'G 0.000 0.000 0.000 K 0.375 0.375 0.750'
wdata(11) = 'K 0.375 0.375 0.750 X 0.500 0.000 0.500'
wdata(12) = 'end kpoint_path'
wdata(13) = 'bands_num_points = 10'
wdata(14) = 'guiding_centres = .true.'

prtgkk = .true.
iverbosity = 2
fsthick = 0.4
degaussw = 0.1
degaussq = 0.05
fermi_plot = .true.
ephwrite = .true.
eliashberg = .true.
liso = .true.
limag = .true.
!lpade = .true. ! solve ME eqs. on real axis using Pade approximants
!lacon = .true. ! analytic continuation of ME eqs. from imaginary to real axis
nsiter = 500
npade = 40 ! percentage of Matsubara points used in Pade continuation.
conv_thr_iaxis = 1.0d-3
conv_thr_racon = 1.0d-3
wscut = 1.0 ! upper limit over Matsubara freq. summation in ME eqs on imag.axis in [eV]
muc = 0.13 ! effective Coulomb potential used in the ME eqs.
temps = 3.0 6.0 9.0 12.0 15.0 18.0 21.0 24.0 27.0 31.0
mp_mesh_k = .false. ! use irreduciable electronic fine mesh
nkf1 = 8
nkf2 = 8
nkf3 = 8
nk1 = 16
nk2 = 16
nk3 = 16
nq1 = 8
nq2 = 8
nq3 = 8
nqf1 = 8
nqf2 = 8 ! dimensions of the fine phonon grid
nqf3 = 8
/
And some output is
iq = 2 coord.: 0.0000000 0.0000000 0.1250000
ik = 1 coord.: 0.0000000 0.0000000 0.0000000
ibnd jbnd imode enk[eV] enk+q[eV] omega(q)[meV] |g_sym|[meV] |g|[meV] Re(g)[meV] Im(g)[meV]
------------------------------------------------------------------------------
1 1 1 -0.0273 0.2531 7.3277844403 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
1 1 2 -0.0273 0.2531 7.3277844403 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
1 1 3 -0.0273 0.2531 26.9984373257 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
------------------------------------------------------------------------------

ik = 2 coord.: 0.0000000 0.0000000 0.1250000
ibnd jbnd imode enk[eV] enk+q[eV] omega(q)[meV] |g_sym|[meV] |g|[meV] Re(g)[meV] Im(g)[meV]
------------------------------------------------------------------------------
1 1 1 0.2531 1.1112 7.3277844403 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
1 1 2 0.2531 1.1112 7.3277844403 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
1 1 3 0.2531 1.1112 26.9984373257 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
------------------------------------------------------------------------------

ik = 3 coord.: 0.0000000 0.0000000 0.2500000
ibnd jbnd imode enk[eV] enk+q[eV] omega(q)[meV] |g_sym|[meV] |g|[meV] Re(g)[meV] Im(g)[meV]
------------------------------------------------------------------------------
1 1 1 1.1112 2.4624 7.3277844403 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
1 1 2 1.1112 2.4624 7.3277844403 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
1 1 3 1.1112 2.4624 26.9984373257 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00 0.0000000000E+00
now for the second case I have input
&inputepw
prefix = 'li_30GPa',
amass(1) = 6.941,
outdir = './tmp'
dvscf_dir = '/home/numan/li_epw_q-e7.5/phonon_lda_30GPa_8x8x8/save'
!ep_coupling = .true. ! run e-ph coupling calculation
elph = .true. ! calculate e-ph coefficients
epwwrite = .true. ! write e-ph matrices in Wann representation
epwread = .false. ! read e-ph matrices from 'prefix.epmatwp' file
wannierize = .true.
nbndsub = 1
bands_skipped = 'exclude_bands = 1, 3-6'
!efermi_read = .true.
!fermi_energy = 3.9092
num_iter = 300
dis_win_min = -0.0273
dis_win_max = 9.1842
dis_froz_min = -0.0265
dis_froz_max = 9.0000
proj(1) = 'Li:s'
wannier_plot= .true.
wdata(1) = 'bands_plot = .true.'
wdata(2) = 'dis_num_iter = 1000'
wdata(3) = 'dis_conv_tol = 1E-11'
wdata(4) = 'conv_tol = 1E-11'
wdata(5) = 'begin kpoint_path'
wdata(6) = 'G 0.000 0.000 0.000 L 0.500 0.500 0.500'
wdata(7) = 'L 0.500 0.500 0.500 W 0.500 0.250 0.750'
wdata(8) = 'W 0.500 0.250 0.750 X 0.500 0.000 0.500'
wdata(9) = 'X 0.500 0.000 0.500 G 0.000 0.000 0.000'
wdata(10) = 'G 0.000 0.000 0.000 K 0.375 0.375 0.750'
wdata(11) = 'K 0.375 0.375 0.750 X 0.500 0.000 0.500'
wdata(12) = 'end kpoint_path'
wdata(13) = 'bands_num_points = 10'
wdata(14) = 'guiding_centres = .true.'

prtgkk = .true.
mp_mesh_k = .false. ! use irreduciable electronic fine mesh
nkf1 = 8
nkf2 = 8
nkf3 = 8
nk1 = 16
nk2 = 16
nk3 = 16
nq1 = 8
nq2 = 8
nq3 = 8
nqf1 = 8
nqf2 = 8 ! dimensions of the fine phonon grid
nqf3 = 8
/

and output is
Electron-phonon vertex |g| (meV)

iq = 2 coord.: 0.0000000 0.0000000 0.1250000
ik = 1 coord.: 0.0000000 0.0000000 0.0000000
ibnd jbnd imode enk[eV] enk+q[eV] omega(q)[meV] |g_sym|[meV] |g|[meV] Re(g)[meV] Im(g)[meV]
------------------------------------------------------------------------------
1 1 1 -0.0273 0.2531 7.3277844403 0.4943956177E-04 0.4972461239E-04 0.8297652213E-05 -0.4902740097E-04
1 1 2 -0.0273 0.2531 7.3277844403 0.4943956177E-04 0.4915285809E-04 0.1565328749E-04 -0.4659375547E-04
1 1 3 -0.0273 0.2531 26.9984373257 0.2952291472E+02 0.2952291472E+02 0.6977281865E+01 0.2868658277E+02
------------------------------------------------------------------------------

ik = 2 coord.: 0.0000000 0.0000000 0.1250000
ibnd jbnd imode enk[eV] enk+q[eV] omega(q)[meV] |g_sym|[meV] |g|[meV] Re(g)[meV] Im(g)[meV]
------------------------------------------------------------------------------
1 1 1 0.2531 1.1112 7.3277844403 0.2176159602E-04 0.2375243012E-04 0.2274494578E-04 0.6844368345E-05
1 1 2 0.2531 1.1112 7.3277844403 0.2176159602E-04 0.1956926636E-04 -0.1692844594E-04 -0.9817530441E-05
1 1 3 0.2531 1.1112 26.9984373257 0.4500105037E+02 0.4500105037E+02 0.1133933348E+02 0.4354898450E+02
------------------------------------------------------------------------------

ik = 3 coord.: 0.0000000 0.0000000 0.2500000
ibnd jbnd imode enk[eV] enk+q[eV] omega(q)[meV] |g_sym|[meV] |g|[meV] Re(g)[meV] Im(g)[meV]
------------------------------------------------------------------------------
1 1 1 1.1112 2.4624 7.3277844403 0.3133877343E-04 0.3930371982E-04 0.1800344910E-04 0.3493791941E-04
1 1 2 1.1112 2.4624 7.3277844403 0.3133877343E-04 0.2048060176E-04 0.9562587647E-05 0.1811110063E-04
1 1 3 1.1112 2.4624 26.9984373257 0.1004749747E+03 0.1004749747E+03 0.1891643968E+02 0.9867820859E+02

Hi,

In the first case you include a tag "fsthick = 0.4" Which results in the inclusion of only those "k" points (and corresponding k+q points) which fall inside the energy window [Ef-fsthick, Ef+fsthick]. Therefore, some |g| are 0.
In the next case you do not include it and the code defaults to fsthick = 1d10; which results in all "k" falling inside the window. Hence, EPW writes all |g| values.

Hope this helps!

Best regards,
Sabya.

Dear Sabya,

Thanks for your reply. Yeah, it works very well now.

Best regards,
Numan Khan