[Pw_forum] Band gap of AlAs (zinc blende) ‏

[Giuseppe Mattioli]

Dear Ramzi
First of all, this question has been posted half a million of times... 

ibrav=  2

ibrav=  1

You are changing the lattice symmetry, thus folding X into Gamma... You should be able to unfold the 
first Brillouin zone of the simple cubic supercell to find again the original AlAs band structure.

HTH

Giuseppe


On Tuesday 19 June 2012 16:04:26 ramzi alaya wrote:
> I did the band structure of  AlAs (zinc blende) with two atoms and I found
> a indirect gap  (like literature)
> Gamma-X. But when I did it with 8 atoms I found direct gap Gamma -Gamma.
> 
> Why such a problem occurs?
> 
> Thank you for your help
> and advice.
> 
> This is the
> input file for the "nscf" calculation
> 
> 
> With TWO ATOMS:
> 
> 
>  &control
> 
> 
> calculation='nscf'
> 
> 
> restart_mode='from_scratch',
> 
>     tstress =
> .true.
> 
>     tprnfor =
> .true.
> 
> 
> prefix='820-28',
> 
>     pseudo_dir =
> '/home/test/pseudo/',
> 
> 
> outdir='/home/test/tp/'
> 
>  /
> 
>  &system
> 
>     ibrav=  2, celldm(1) =10.64, nat=  2, ntyp= 2,
> 
>     ecutwfc
> =50.0, ecutrho = 200.0, nbnd =8,
> 
>  /
> 
>  &electrons
> 
> 
> diagonalization='david'
> 
>     conv_thr =
> 1.0e-7
> 
>     mixing_beta
> = 0.7
> 
>  /
> 
> ATOMIC_SPECIES
> 
>  al 26.9815  al_pz.upf
> 
>  as 74.9216  as_pz.upf
> 
> ATOMIC_POSITIONS
> 
>  al  0.00 0.00 0.00
> 
>  as  0.250 0.250 0.250
> 
> K_POINTS
> 
>  20
> 
>  0.0000  0.5000
> 1.0000  1
> 
>  0.1000  0.5000
> 0.9000  2
> 
>  0.2000
> 0.5000  0.8000  3
> 
>  0.3000
> 0.5000  0.7000  4
> 
>  0.4000
> 0.5000  0.6000  5
> 
>  0.5000
> 0.5000  0.5000  6
> 
>  0.4000
> 0.4000  0.4000  7
> 
>  0.3000  0.3000
> 0.3000  8
> 
>  0.1000
> 0.1000  0.1000   9 0.0000  0.0000
> 0.0000  10
> 
> 0.0000
> 0.0000  0.1000   11
> 
> 0.0000
> 0.0000  0.2000   12
> 
> 0.0000
> 0.0000  0.3000   13
> 
> 0.0000
> 0.0000  0.4000   14
> 
> 0.0000
> 0.0000  0.5000   15
> 
> 0.0000  0.0000  0.6000
> 16
> 
> 0.0000
> 0.0000  0.7000   17
> 
> 0.0000
> 0.0000  0.8000   18
> 
> 0.0000
> 0.0000  0.9000   19
> 
> 0.0000
> 0.0000  1.0000   20
> 
> 
> 
> and WITH 8 ATOMS:
> 
> 
> &control
> 
> 
> calculation='nscf'
> 
> 
> restart_mode='from_scratch',
> 
>     tstress =
> .true.
> 
>     tprnfor = .true.
> 
>     prefix='820-28',
> 
>     pseudo_dir = '/home/test/pseudo/',
> 
>     outdir='/home/test/tp/'
> 
>  /
> 
>  &system
> 
>     ibrav=
> 1, celldm(1) =10.64, nat=  8,
> ntyp= 2,
> 
>     ecutwfc =50.0, ecutrho = 200.0, nbnd =32,
> 
>  /
> 
>  &electrons
> 
>     diagonalization='david'
> 
>     conv_thr = 1.0e-7
> 
>     mixing_beta = 0.7
> 
>  /
> 
> ATOMIC_SPECIES
> 
>  al 26.9815
> al_pz.upf
> 
>  as 74.9216
> as_pz.upf
> 
> ATOMIC_POSITIONS
> 
> 
> al   0.00000000
> 0.00000000   0.00000000
> 
> al   0.50000000
> 0.50000000   0.00000000
> 
> al   0.50000000
> 0.00000000   0.50000000
> 
> al   0.00000000   0.50000000
> 0.50000000
> 
> as   0.25000000
> 0.25000000   0.25000000
> 
> as   0.75000000
> 0.75000000   0.25000000
> 
> as   0.75000000
> 0.25000000   0.75000000
> 
> as   0.25000000
> 0.75000000   0.75000000
> 
> K_POINTS
> 
>  16
> 
>  0.5000
> 0.5000  0.5000  1
> 
> 0.4000  0.4000
> 0.4000  2
> 
> 0.3000  0.3000
> 0.3000  3
> 
> 0.2000  0.2000
> 0.2000  4
> 
> 
> 
>  0.1000
> 0.1000  0.1000  5
> 
> 0.0000  0.0000
> 0.0000  6
> 
> 0.0000  0.0000
> 0.1000  7
> 
> 0.0000  0.0000
> 0.2000  8
> 
> 0.0000  0.0000
> 0.3000  9
> 
> 0.0000  0.0000
> 0.4000  10
> 
> 0.0000  0.0000
> 0.5000  11
> 
> 0.0000  0.1000
> 0.5000  12
> 
> 0.0000  0.2000
> 0.5000  13
> 
> 0.0000  0.3000
> 0.5000  14
> 
> 0.0000  0.4000
> 0.5000  15
> 
> 0.0000  0.5000
> 0.5000  16
> 
> 
> 
> ***********************************************************
> 
> Ramzi Alaya
> 
> E-mail : ramzialaya at hotmail.fr
> 
> Faculté des Sciences de Gabès, Cité Erriadh 6072 Gabès- Tunisie
> 
> Unité de Recherche sur les Hétéro-Epitaxies et Applications

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   Giuseppe Mattioli                            
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