Error in routine set_u_matrix (1): |xaxis| < eps8

[zanghang]

Dear all,

I'm trying to perform a mobility calculation with QE-7.0+EPW-5.5.

I followed the "GaN-II tutorial", but I got an error of "Error in routine set_u_matrix (1): |xaxis| < eps8" in the step of EPW calculation.
However, I couldn't find the problem in this error message, could you help me to find out the cause of this error?

Thanks very much in advance.

Hang

[hlee]

Dear Hang:

This error is not directly related to the EPW, but it indicates that something wrong happens in your chosen projections for Wannierization.
Could you tell us which inputs you are using and also provide us with all (full) outputs of nscf and epw?

Sincerely,

H. Lee

[zanghang]

Dear H. Lee,

Thanks a lot for your advice.
I found the error is related to the inconsistent of these parameters:
...
nbndsub = 10
...
proj(1) = 'Al:sp3'
proj(2) = 'N:sp3'
...

I used an AlN unit cell model containing 2 Al and 2 N atoms, after I changed nbndsub = 16, this error was fixed.


Below is the full input file for the EPW interpolation step I used
==================================================================================================
--
&inputepw
prefix = 'aln'
outdir = './'

iverbosity = 0

elph = .true.
epbwrite = .true.
epbread = .false.
epwwrite = .true.
epwread = .false.
etf_mem = 1
vme = 'wannier'

lpolar = .true.
lifc = .false.
asr_typ = 'simple'
use_ws = .false.
lphase = .true.

nbndsub = 10
bands_skipped = 'exclude_bands = 1-2'


wannierize = .true.
num_iter = 1500
iprint = 3
dis_win_max = 15.0
dis_win_min = 0.0
dis_froz_max= 10.0
proj(1) = 'Al:sp3'
proj(2) = 'N:sp3'
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) = 'G 0.00 0.00 0.00 K 0.33333333333 0.33333333333 0.00'
wdata(5) = 'G 0.00 0.00 0.00 A 0.00 0.00 0.50'
wdata(6) = 'end kpoint_path'
wdata(7) = 'bands_plot_format = gnuplot'
wdata(8) = 'guiding_centres = .true.'
wdata(9) = 'dis_num_iter = 1000'
wdata(10) = 'num_print_cycles = 10'
wdata(11) = 'dis_mix_ratio = 1.0'
wdata(12) = 'conv_tol = 1E-8'
wdata(13) = 'conv_window = 4'

elecselfen = .false.
phonselfen = .false.
a2f = .false.

fsthick = 100.0 ! eV
temps = 1 ! K
degaussw = 0.01 ! eV

dvscf_dir = './save/'

efermi_read = .true
fermi_energy= 8.1483
band_plot = .true.

filkf = './MGA.txt'
filqf = './MGA.txt'


nk1 = 5
nk2 = 5
nk3 = 2
nq1 = 5
nq2 = 5
nq3 = 2
/
==================================================================================================

Sincerely,
Hang