Mismatch in Fermi energies

[appalakondaiah]

Dear all,

I am trying to calculate Superconducting properties of 2D-TMD's as given in MgB2 tutorial. My calculations are successful and confused with the

coarse and fine K-mesh fermi energies

in epw.out.

Fermi energy coarse grid = 1.548307 eV

Skipping the first 2 bands:

The Fermi level will be determined with 14.08000 electrons

Fermi energy is calculated from the fine k-mesh: Ef = -2.499372 eV

.

My wannier spreads also looking fine with max of 1.5 Ang. Kindly see my below input and suggest any solution for fixing the same

&inputepw
prefix = '$NAME'
amass(1) = 183.84,
amass(2) = 32.05,
outdir = '$TMP/epw/'

iverbosity = 0

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

etf_mem = .false.
system_2d = .true.

epwwrite = .true.
epwread = .false.

nbndsub = 11
nbndskip = 2
wannierize = .true.
num_iter = 500
dis_win_max = 3.8
dis_froz_max= 1.8
proj(1) = 'W:d'
proj(2) = 'S: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 '

elecselfen = .true.
phonselfen = .true.
a2f = .true.

parallel_k = .true.
parallel_q = .false.

fsthick = 4.0 ! eV
eptemp = 300 ! K (same as PRB 76, 165108)
degaussw = 0.2 ! eV


dvscf_dir = '$TMP/save/'
filukk = './WS2.ukk'

nkf1 = 60
nkf2 = 60
nkf3 = 1

nqf1 = 60
nqf2 = 60
nqf3 = 1

nk1 = 12
nk2 = 12
nk3 = 1

nq1 = 12
nq2 = 12
nq3 = 1

Thanks in Advance

with regards
S. Appalakondaiah

[roxana]

Hi,

The first Fermi energy (1.54 eV in this case) corresponds to the nscf calculation on the coarse k-mesh, while the second Fermi energy (-2.499 eV in this case) corresponds to the epw calculation on the fine k-mesh. These values should be very close unless you read the Fermi energy from the input file.

I also noticed that the nr of electrons is not an integer, but 14.08 electrons. Is this correct? Are you skipping the correct bands? Have you plotted the wannier band structure on top of the DFT band structure to check if it is well described?

Best,
Roxana

[appalakondaiah]

Dear Prof,

Yes. I checked with all bands (also, my wannier spreads looking fine) and still the variation in the fermi energies using Fine and coarse grids were seen. Also, My band profiles are almost similar in both cases such as Standard DFT and wannier methods.
Here I am making my semiconductor system into metallic using carrier dope method (with flag total_charge) in nscf calculations. so, number of electrons should be non-integer.

Kindly suggest me the path to solve my error

with regards
S. Appalakondaiah

[roxana]

Hi,

Such discrepancy can appear if nbndsub or nbndskip are not setup correctly. Please send the plot with the wannier band structure obtained with EPW on top of the DFT band structure. Also show the part of the bands that you skip.

Best,
Roxana