EPW Forum

Dear all,

I am using QE-6.8. Something is wrong when I try to use epw.x,
the error message is "Error in routine epw_setup (1): coarse k-mesh needs to be strictly positive in 1st BZ"

I feel confused about this question, so I want to seek help on the forum. Thank you.

here is my epw.in:
--
&inputepw
prefix = 'mos'
amass(1) = 95.96
amass(2) = 32.065
outdir = './'
dvscf_dir = '../phonon/save'

elph = .true.
epwwrite = .true.
epwread = .false.
lpolar = .true.

wannierize = .true.
nbndsub = 34
num_iter = 2000
proj(1) = 'Mo:s;p;d'
proj(2) = 'S:s;p'
dis_win_max = 10
dis_froz_max = 2.5
dis_froz_min = -40
dis_win_min = -40
wdata(1) = 'spinors = .true.'

prtgkk = .true.

filqf = 'path1.dat'
nkf1 = 1
nkf2 = 1
nkf3 = 1

nk1 = 12
nk2 = 12
nk3 = 2
nq1 = 3
nq2 = 3
nq3 = 3
/

here is my nscf.in:

&CONTROL
calculation = 'nscf'
etot_conv_thr = 3.0000000000d-05
forc_conv_thr = 1.0000000000d-04
outdir = './'
prefix = 'mos'
pseudo_dir = '../pseudo/'
tprnfor = .true.
tstress = .true.
verbosity = 'high'
/
&SYSTEM
degauss = 1.4699723600d-02
ecutrho = 2.8000000000d+02
ecutwfc = 3.5000000000d+01
ibrav = 0
! celldm(1) = 3.1840500832
! celldm(3) = 5.69306
nat = 3
nosym = .true.
nspin = 4
noncolin = .true.
lspinorb = .true.
ntyp = 2
occupations = 'smearing'
smearing = 'cold'
starting_magnetization(1) = 3.5714285714d-01
starting_magnetization(2) = 1.0000000000d-01
/
&ELECTRONS
conv_thr = 6.0000000000d-10
electron_maxstep = 80
mixing_beta = 4.0000000000d-01
/
ATOMIC_SPECIES
Mo 95.96 Mo_ONCV_PBE-1.0.oncvpsp.upf
S 32.065 s_pbe_v1.4.uspp.F.UPF
ATOMIC_POSITIONS crystal
Mo 0.0000000000 0.0000000000 0.5000000000
S 0.6666669850 0.3333329860 0.5862550140
S 0.6666669850 0.3333329860 0.4137449860
K_POINTS automatic
12 12 2 0 0 0
CELL_PARAMETERS angstrom
3.1840500832 0.0000000000 0.0000000000
-1.5920250416 2.7574682589 0.0000000000
0.0000000000 0.0000000000 18.1270008087

I have checked that the number of k points in nscf.out is the same as nscf.in.
I have tried to use another input with symmetry (i.e. ibrav=4, nosym=.false.),
while the same error message also occurs.

Sincerely,
jykun

Hi Jykun,

The error message explains clearly "coarse k-mesh needs to be strictly positive in 1st BZ". The uniform k-mesh you have provided in the 'nscf.in' are not positive in the 1st BZ, need to define a homogeneous k-grid. I suggest, the homogeneous k grid for the non self-consistent calculations can be generated using the script 'kmesh.pl' script provided in the wannier90-xx/utility source code, for example " .../q-e/wannier90-3.1.0/utility/kmesh.pl 12 12 2" for the 12x12x2 k-mesh. Some tutorials are available in the EPW website https://docs.epw-code.org/doc/Tutorials.html, might be helpful.

Happy EPWing,
Hari