[Pw_forum] Band gap of AlAs (zinc blende)‏

[ramzi alaya]

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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