[Pw_forum] ZB ZnO vs WZ ZnO at HSE level

[giacsport at libero.it]

Dear All,               I have a doubt I am not able to fix by myself. I am doing an "scf" spin polarized calculation for both the ZB and the WZ form of ZnO, at HSE level, with the development version of PWscf.  For what regard the pseudo of Zn, I am using one with 2e only in the valence (PRB 81, 125207 (2010)). What I notice is that the DeltaE between the two systems is huge (4.4 Ry), with a macroscopic error on the bandgap of ZB-ZnO. Can this only be ascribed to the small number  of electrons in the valence? I here report the two input files for both systems. I moreover think that the downsampling of the Fock exchange operator (q) can not be so much influent. But maybe I am wrong
Thanks in advance for any hint you may give me.

Best,  
Giacomo---------------------------------





Giacomo Giorgi

Department of Chemical System Engineering,

School of Engineering, The University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

E-mail: giacomo at tcl.t.u-tokyo.ac.jp








1) WZ-ZnO
&SYSTEM
    ibrav=  4, celldm(1) =6.140475627, celldm(3)=1.6014648858250753985351141749246, nat=  4, ntyp= 2,
    ecutwfc =80.0,  nbnd = 20,force_symmorphic=.true., nspin=2, tot_magnetization=0,
    input_dft='hse', nqx1 = 2, nqx2 = 2, nqx3 = 1,
    x_gamma_extrapolation = .TRUE.
/
&ELECTRONS
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-8
/
ATOMIC_SPECIES
 Zn  65.409  Zn_pz-2_nlcc.cpi.UPF
  O  15.999  O.pz-mt.UPF
ATOMIC_POSITIONS (crystal)
  Zn    0.33333   0.66667   0.00000
  Zn    0.66667   0.33333   0.50000
  O     0.33333   0.66667   0.38210
  O     0.66667   0.33333   0.88210
K_POINTS (automatic)
8 8 6 0 0 0

for this one I get (and it seems a reasonable result, at least from the gap)

 highest occupied, lowest unoccupied level (ev):     1.4320    5.2338 total energy              =    -110.48522966 Ry








2) ZB-ZnO
&system
    ibrav=  2, celldm(1) =8.447075169
    nat=  8, ntyp= 2, force_symmorphic=.true., nspin=2, tot_magnetization=0,
    ecutwfc =80.,  nbnd = 50,
    input_dft='hse', nqx1=2, nqx2=2, nqx3=2,
    x_gamma_extrapolation = .TRUE.
/
&electrons
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-8
/
ATOMIC_SPECIES
 Zn  65.38     Zn_pz-2_nlcc.cpi.UPF
  O  15.9994   O.pz-mt.UPF
ATOMIC_POSITIONS (crystal)
  Zn    0.00000   0.00000   0.00000
  Zn    0.00000   0.50000   0.50000
  Zn    0.50000   0.00000   0.50000
  Zn    0.50000   0.50000   0.00000
  O     0.25000   0.25000   0.25000
  O     0.25000   0.75000   0.75000
  O     0.75000   0.75000   0.25000
  O     0.75000   0.25000   0.75000
K_POINTS automatic
8 8 8 0 0 0

For this one I get (!!)

highest occupied, lowest unoccupied level (ev):    36.4937   31.9513  (!!!) 
total energy              =    -200.32746186 Ry
 
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