[Pw_forum] problem in electronic structure of ZnO

[zafar rasheed]

Dear Eyvaz Isaaev
 
    I want to calculate electronic band structure of w-ZnO (1x1x2 super cell). But output band strcuture is overlaped. Whereas the band structure of w-ZnO unit cell is same as theoretical and experimental. I make this supercell using PHON code. Due to increase in cell along z-axis  I increase its lattice parameter c 2 times in inputs (celldm=2*c/a). The inputs are attcahed below.
   



 &control

    Title = 'ZnO , hcp,a=3.2500,c=5.206
,c/a=1.6103125',

    calculation ='scf'
                
                 

    restart_mode='from_scratch',

    pseudo_dir  =
'/root/Pwscf/pseudo/',

    outdir     
='/root/Pwscf/scratch/'

    prefix      ='ZnO'

    tstress     = .false.

    tprnfor     = .false.

 /

 &system

    ibrav=  4, 

    celldm(1)   = 6.132075472,

    celldm(3)   = 1.601846154,

    nat         =4, 

    ntyp        =2,

    ecutwfc     =25.0,

    ecutrho     =300.0 

    occupations ='smearing',

     smearing='methefessel_paxton',

     degauss  = 0.02, 


 /

 &electrons

    diagonalization='cg' ,

    conv_thr    = 1.0e-8      	

    mixing_beta = 0.7 

 /

ATOMIC_SPECIES

 Zn   65.409   Zn.pz-van_ak.UPF

 O    15.9994  O.pz-van_ak.UPF		

ATOMIC_POSITIONS (crystal)

  Zn 0.333333333  0.666666667  
0.0000000

   O 0.333333333  0.666666667  
0.3817000

  Zn 0.666666667  0.333333333  
0.5000000

   O 0.666666667  0.333333333  
0.8817000

K_POINTS (automatic)

7 7 7  0  0  0






This plot (after changing scf to nscf)
is same as experimental and theoretical 







BUT



when I make a cell of 8 atoms (1x1x2
supercell)
 input is as below






 &control

    calculation ='nscf' <= or bands


    restart_mode='from_scratch',

    pseudo_dir  =
'/root/Pwscf/pseudo/',

    outdir     
='/root/Pwscf/scratch/'

    prefix      ='ZnO'

    tstress     = .false.

    tprnfor     = .true.

 /

 &system

    ibrav       = 4, 

    celldm(1)   = 6.132075472,

    celldm(3)   = 3.203692308,

(due to increase in size along Z-direction C= 2*c )
    nat         = 8, 

    ntyp        = 2,

    ecutwfc     = 25.0, 

    ecutrho     = 300.0

    occupations ='smearing', 

    smearing    ='methefessel_paxton', 

    degauss     =0.02 nbnd=20 nosym=.true.


 /

 &electrons

    diagonalization='cg'
,mixing_mode='plain',

    conv_thr    = 1.0e-8

    mixing_beta = 0.7

 /

ATOMIC_SPECIES

  Zn   65.38 Zn.pz-van_ak.UPF

   O    16.00 O.pz-van_ak.UPF		

ATOMIC_POSITIONS (crystal)

 Zn  0.333333333   0.666666667  
0.000000000

 Zn  0.333333333   0.666666667  
0.500000000

 Zn  0.666666667   0.333333333  
0.250000000

 Zn  0.666666667   0.333333333  
0.750000000

  O  0.333333333   0.666666667  
0.190850000

  O  0.333333333   0.666666667  
0.690850000

  O  0.666666667   0.333333333  
0.440850000

  O  0.666666667   0.333333333  
0.940850000

K_POINTS 
32 
   0.0   0.0  0.5  1
   0.1  -0.1  0.1  2
   0.2  -0.2  0.2  3
   0.3  -0.3  0.3  4
   0.4  -0.4  0.4  5
   0.5  -0.5  0.5  6
   0.5  -0.5  0.4  7
   0.5  -0.5  0.3  8
   0.5  -0.5  0.2  9
   0.5  -0.5  0.1  10
   0.5  -0.5  0.0  11
   0.4  -0.4  0.0  12
   0.3  -0.3  0.0  13
   0.2  -0.2  0.0  14
   0.1  -0.1  0.0  15
   0.0   0.0  0.0  16
   0.0   0.0  0.1  17
   0.0   0.0  0.2  18
   0.0   0.0  0.3  19
   0.0   0.0  0.4  20
   0.0   0.0  0.5  21
   0.11  0.11  0.5 22
   0.22  0.22  0.5 23
   0.33  0.33  0.5 24
   0.33  0.33  0.4 25
   0.33  0.33  0.3 26
   0.33  0.33  0.2 27
   0.33  0.33  0.1 28
   0.33  0.33  0.0 29
   0.22  0.22  0.0 30
   0.11  0.11  0.0 31
   0.00  0.00  0.0 32



   




After changing scf to bands the
electronic structure is metallic (no band gap) and a I get different
electronic structure . Now please guide me how I can get true
electronic structure.



Thanking in Advance

Muhammad Zafar

PhD Scholar

Department of Physics

The Islamia University of Bahawalpur,Pakistan
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