[Pw_forum] How to get the usual ~2.4 eV band gap of ZnO with HSE06?

[Tan Hengxin]

Dear all,

I am doing some calculations on the HSE06 (25% EXX) band gap of wurtzite
ZnO with experimental structure, and find that I cannot get the usual value
of ~2.4 eV. My value is just ~2.1 eV.
Maybe my norm-conserving pseudopotentials (NC-PPs) of Zn and O are not very
good. So I also tried the NC-PPs for Zn and O from the pslibrary.0.3.1.
However, the gap is even smaller (~1.8 eV). (All PPs are based on PBE xc.)
I have also done different tests with different parameters, containing
nbnd, nqx1, nqx2, nqx3, k-mesh. But I still cannot get 2.4 eV for the HSE
gap.

So could anyone provide a guidance on how to obtain the usual HSE band gap
of 2.4 eV for wurtzite ZnO ? The input parameters are as follows, and the
output file calculated with the NC-PPs from the pslibrary.0.3.1 is also
attached. Thank you in advance!

My input parameters for the scf run:
&CONTROL
  calculation   = 'scf',
  prefix        = 'ZnO',
  pseudo_dir    = './',
! nstep         = 200,
  verbosity     = 'high',
  wf_collect    = .true.
  etot_conv_thr = 1.0D-5,
  forc_conv_thr = 1.0D-4,
  restart_mode  = 'from_scratch',
  outdir        = './temp_out',
/
&SYSTEM
  ibrav         = 0,
! celldm(1)     = 1.88972688,
  nat           = 4,
  ntyp          = 2,
  ecutwfc       = 60,
! ecutrho       = 240,
! nosym         = .true.
  nbnd          = 36,
! occupations   = 'smearing',
! degauss       = 0.000367,
! smearing      = 'gaussian',
  input_dft     = 'hse',
  exx_fraction  = 0.25,
! screening_parameter = 0.106
! exxdiv_treatment    = gygi-baldereschi
  nqx1 = 3, nqx2 = 3, nqx3 = 2,
! nspin         = 2
! starting_magnetization(1) = 1.0,
! starting_magnetization(2) = -1.0,
! lda_plus_u    = .true.
! hubbard_U(5)  = 2.59,
! hubbard_alpha(2) = 0.d0,
! hubbard_U(2)     = 3,
/
&ELECTRONS
! electron_maxstep = 100,
  mixing_mode   = 'plain',
  mixing_beta   = 0.7,
  conv_thr      = 1.D-8,
! startingwfc   ='atomic+random',
! startingpot   ='atomic',
/
&IONS
  ion_dynamics      = 'bfgs',
  pot_extrapolation = 'atomic',
  upscale           = 100,
  trust_radius_ini  = 0.5,
/
&CELL
  cell_dynamics     = 'bfgs',
  press_conv_thr    = 0.5,
  cell_dofree       = 'all',
/

ATOMIC_SPECIES
 Zn 65.38     Zn.pbe-nc.UPF
 O  15.999    O.pbe-nc.UPF

CELL_PARAMETERS (angstrom)
     3.249         0.000         0.000
    -1.625         2.814         0.000
     0.000         0.000         5.205

ATOMIC_POSITIONS (crystal)
Zn    0.333333343         0.666666687         0.000000000
Zn    0.666666627         0.333333313         0.500000000
O     0.333333343         0.666666687         0.382600009
O     0.666666627         0.333333313         0.882600009

K_POINTS {automatic}
 9 9 6 0 0 0

Regards,
Hengxin Tan, PhD
Department of Physics
Tsinghua University.
-- 

Tan Hengxin
Department of physics, THU.
Beijing 100084, China
Office: B403,New Science Building
E-mail:t <E-mail%3Athx13 at mails.tsinghua.edu.cn>anhx90 at gmail.com
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