EPW Forum

Dear users
I want to study the superconductivity of MgB2 in the presence of an electric fields. I modified the example mgb2 and my inputs are as follows:

scf.in:



&control
calculation='scf',
prefix='MgB2',
pseudo_dir = '../pp/',
outdir='./',
tefield=.true.,
tprnfor = .true.,
tstress = .true.,
etot_conv_thr = 1.0d-5
forc_conv_thr = 1.0d-4
/
&system
ibrav = 4,
celldm(1) = 5.8260252227888,
celldm(3) = 1.1420694129095,
nat= 3,
ntyp = 2,
ecutwfc = 40
smearing = 'mp',force_symmorphic= .true.,
occupations = 'smearing'
degauss = 0.02
/
&electrons
diagonalization = 'david'
mixing_mode = 'plain'
mixing_beta = 0.7
conv_thr = 1.0d-9
epol = 3
efield = 0.001
/
ATOMIC_SPECIES
Mg 24.305 Mg.pz-n-vbc.UPF
B 10.811 B.pz-vbc.UPF
ATOMIC_POSITIONS crystal
Mg 0.000000000 0.000000000 0.000000000
B 0.333333333 0.666666667 0.500000000
B 0.666666667 0.333333333 0.500000000
K_POINTS AUTOMATIC
12 12 12 0 0 0


ph.in:
--
&inputph
prefix = 'MgB2',
fildyn = 'MgB2.dyn',
amass(1) = 24.305,
amass(2) = 10.811,
outdir = './'
ldisp = .true.,
trans = .true.,
fildvscf = 'dvscf',
nq1=2,
nq2=2,
nq3=2,
tr2_ph = 1.0d-14
/
and
and 30 last line of epw.in :

dvscf_dir = '../phonons/save'

nk1 = 6
nk2 = 6
nk3 = 6

nq1 = 2
nq2 = 2
nq3 = 2

mp_mesh_k = .true.
nkf1 = 20
nkf2 = 20
nkf3 = 20

nqf1 = 20
nqf2 = 20
nqf3 = 20
/
8 cartesian
0.000000000000000E+00 0.000000000000000E+00 0.000000000000000E+00 1.00
0.000000000000000E+00 0.000000000000000E+00 -0.437801760863393E+00 1.00
0.000000000000000E+00 -0.577350269189585E+00 0.000000000000000E+00 1.00
0.000000000000000E+00 -0.577350269189585E+00 -0.437801760863393E+00 1.00
-0.500000000000000E+00 -0.288675134594792E+00 0.000000000000000E+00 1.00
-0.500000000000000E+00 -0.288675134594792E+00 -0.437801760863393E+00 1.00
-0.500000000000000E+00 -0.866025403784377E+00 0.000000000000000E+00 1.00
-0.500000000000000E+00 -0.866025403784377E+00 -0.437801760863393E+00 1.00

However when I run epw.x I faced this error:

forrtl: severe (59): list-directed I/O syntax error, unit 81, file /home/nano/Desktop/espresso-5.4.0/EPW/examples/mgb2/epw/../phonons/save/MgB2.dyn_q3
Image PC Routine Line Source
epw.x 0000000000DEFDC6 Unknown Unknown Unknown
epw.x 0000000000E21B97 Unknown Unknown Unknown
epw.x 0000000000E1FDF5 Unknown Unknown Unknown
epw.x 00000000004833BD readmat_shuffle2_ 267 readmat_shuffle2.f90
epw.x 0000000000445509 elphon_shuffle_wr 358 elphon_shuffle_wrap.f90
epw.x 000000000040624B MAIN__ 139 epw.f90
epw.x 000000000040572E Unknown Unknown Unknown
libc.so.6 00007F3D9BEEA76D Unknown Unknown Unknown
epw.x 0000000000405639 Unknown Unknown Unknown


what can I do to remove error? It should be noted that when we turn on the electric filed, all symmetries have been removed .
Thanks a lot

Ali Kazempour, Physics Dept., Pnu University, Yazd , Iran

Dear Ali,

mp_mesh_k = .true. flag implies that symmetry is used in order to find the irreducible k-points.
You can try to see if removing this flag helps. However, I should point out that EPW has not been tested for a QE calculation in the presence of an electric field.

Best,
Roxana

Dear Roxana
I change the switch to mp_mesh_k = .false., But face another error


# WARNING: there are pending errors
# PENDING ERROR (ierr=1)
# ERROR IN: iotk_open_read (iotk_files.f90:611)
# CVS Revision: 1.20
# unit
file=../phonons/save/diam.phsave/patterns.1.xml
binary=F
iostat=29
# FROM IOTK LIBRARY, VERSION 1.2.0
# UNRECOVERABLE ERROR (ierr=2)
# ERROR IN: iotk_getline (iotk_scan.f90:947)
# CVS Revision: 1.23
#
iostat=29
# ERROR IN: iotk_scan_tag (iotk_scan.f90:593)
# CVS Revision: 1.23
# ERROR IN: iotk_scan (iotk_scan.f90:821)
# CVS Revision: 1.23
# ERROR IN: iotk_scan_begin (iotk_scan.f90:98)
# CVS Revision: 1.23

I geuss the reason is espresso cann't work DFPT with external electric field.? What do you suggest?

Bests

Dear Ali,

I found the following paragraph in QE user guide, where it is stated that ph.x code doesn't work with external electric fields.

"The main code ph.x can be used whenever PWscf can be used, with the exceptions of:
DFT+U, semiempirical VdW corrections, nonlocal vdW and hybrid functionals, external elec-
tric fields, constraints on magnetization, nonperiodic boundary conditions. USPP and PAWare
not implemented for higher-order response calculations. See the header of file PHonon/PH/phonon.f90
for a complete and updated list of what PHonon can and cannot do."

I am afraid we cannot help you with the ph.x code and I would suggest you post your question on the QE forum.

Best,
Roxana

Dear Ali,

As stated by Roxana, EPW rely on el-ph matrix elements produced by QE.
We therefore support as much (or less) as QE/PH code supports.

In this case, EPW does not indeed support external electric field.

Best,

Samuel