[Pw_forum] WZ and ZB ZnO

[giacsport at libero.it]

Dear all,             regardless the pseudopotentials I use for my optimization and the kpoint sampling, I always obtain that ZB phase of ZnO is (slightly) more stable than WZ.
Since I would like to make HSE calculations on such systems I would like to have an already  well-ordered (in terms of energy, of course) structures at PBE level. (In my case WZ and ZB look almost degenerate, but always with ZB slightly more stable than WZ)

Can anyone help me to refine parameters that allow me to obtain E WZ < E ZB. Here you find the two inputs.
Wurtzite ZnO&CONTROL
    calculation = "scf"
    pseudo_dir = './'
    outdir='./',
    restart_mode="from_scratch",
    prefix='ZnO_WZ',
    tprnfor     = .true.,
    tstress     = .true.,
    wf_collect=.true.,
/
&SYSTEM
    ibrav=  4, celldm(1) =6.13821, celldm(3)=1.6023951, nat=  4, ntyp= 2,
    ecutwfc =90.0,  nbnd = 80, nspin=2, tot_magnetization=0,
/
&ELECTRONS
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-8
/
ATOMIC_SPECIES
 Zn  65.38     Zn-GGA-pbe.fhi.UPF
  O  15.9994    O-GGA-pbe.fhi.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)
12 12 9 0 0 0

total energy              =    -285.55060915 Ry/2 = -142.7753045750



Zincblende ZnO&control
    calculation = 'scf'
    restart_mode='from_scratch',
    prefix='ZnO_ZB',
    tprnfor     = .true.,
    tstress     = .true.,
    wf_collect=.true.,
    pseudo_dir='./',
    outdir='./',
/
&system
    ibrav=  1, celldm(1) =8.730534067
    nat=  8, ntyp= 2,
    ecutwfc =90.,  nbnd = 100, nspin=2, tot_magnetization=0
/
&electrons
    diagonalization='david'
    mixing_mode = 'plain'
    mixing_beta = 0.7
    conv_thr =  1.0d-8
/
ATOMIC_SPECIES
 Zn  65.38     Zn-GGA-pbe.fhi.UPF
  O  15.9994   O-GGA-pbe.fhi.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

total energy              =    -571.10793352 Ry/4 = -142.776983375


Thanks in advance for your help!
Very best,Giacomo

-- 

***************************************

Giacomo Giorgi, Ph.D.



Yamashita & Ushiyama Laboratory,

Department of Chemical System Engineering,

Faculty of Engineering,

The University of Tokyo.



tel&fax: +81-3-5841-7286

email: giacomo at tcl.t.u-tokyo.ac.jp

HP: http://www.tcl.t.u-tokyo.ac.jp/

***************************************
 
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