[Pw_forum] Re : Band gap of BN (zinc blende)

[Said Asma]

Dear Layla,
Thank you for your answer, normally if we change (nat = 2, ibrav = 2) to (nat = 8, ibrav = 1),we find the same nature of gap.
If such we have the composition B0.25Ga0.75N how we can determine the nature of gap?

bests

Said Asma



________________________________
 De : Layla Martin-Samos <lmartinsamos at gmail.com>
À : Said Asma <saidasma1987 at yahoo.fr> 
Cc : "pw_forum at pwscf.org" <pw_forum at pwscf.org> 
Envoyé le : Mercredi 18 avril 2012 15h45
Objet : Re: [Pw_forum] (no subject)
 

Dear Said, it is not a problem, I think, as increasing the number of atoms will fold the Brillouin zone into gamma. 

bests

Layla


2012/4/18 Said Asma <saidasma1987 at yahoo.fr>


>
>Dear PWScf Users,
>
>I did the band structure of BN(zinc blende) with two atoms and I found aindirectgap  (like literature) Gamma-X. But when I did it with 8 atoms I found direct gap Gamma -Gamma.
>
>Why such a problem occurs?
>
>My input files is as following:
> 
> *With TWO ATOMS:
>
>cat > bn.band.in << EOF
> &control
>    calculation='bands'
>    pseudo_dir = '$PSEUDO_DIR/',
>    outdir='$TMP_DIR/',
>    prefix='bn'
> /
> &system
>    ibrav=  2, celldm(1) = 6.76, nat=  2, ntyp= 2,
>    ecutwfc = 60.0,
>    occupations ='smearing',
>    smearing = 'methfessel-paxton',
>    degauss= 0.03,
> /
> &electrons
>                 conv_thr = 1.0d-7 ,
>                 mixing_mode = 'plain' ,
>                 mixing_beta = 0.2
 ,
>                 diagonalization = 'david' ,
> /
>ATOMIC_SPECIES
> B  10.811  B.pz-vbc.UPF
> N  14.007  N.pz-vbc.UPF
>ATOMIC_POSITIONS
>  B 0.00 0.00 0.00
>  N 0.25 0.25 0.25
>K_POINTS {crystal_b}
>5
>0.5  0.5  0.5  400
>0    0    0    400
>1.0  0    0    400
>0.75 0.75 0    400
>0    0    0    400
>EOF
>$ECHO "  running the band-structure calculation for bn...\c"
>$PW_COMMAND < bn.band.in > bn.band.out
>check_failure $?
>$ECHO " done"
>
>
>
>*and WITH 8 ATOMS:
>
>cat > bn.band.in << EOF
> &control
>    calculation='bands'
>    pseudo_dir = '$PSEUDO_DIR/',
>    outdir='$TMP_DIR/',
>    prefix='bn'
> /
> &system
>    ibrav= 1, celldm(1) = 6.82, nat=8, ntyp= 2,
>    ecutwfc = 40.0, nbnd = 40,
>    occupations ='smearing',
>    smearing = 'methfessel-paxton',
>    degauss= 0.02,
> /
> &electrons
>  conv_thr =  1.0d-7,
>    mixing_beta = 0.2,
> /
>
>ATOMIC_SPECIES
> B  10.811  B.pz-vbc.UPF
> N  14.007  N.pz-vbc.UPF
>ATOMIC_POSITIONS
> B      0.000     0.000     0.000
> N      0.250     0.250     0.250
> B      0.000     0.500     0.500
> N      0.250     0.750     0.750
> B      0.500     0.500     0.000
> N      0.750     0.250     0.750
> B      0.500     0.000     0.500
> N      0.750     0.750     0.250
>
>K_POINTS {crystal_b}
>4
>0    0    0    40
>0.5  0    0    40
>0.5  0.5  0    40
>0    0    0    40
>EOF
>$ECHO "  running the band-structure calculation for bn...\c"
>$PW_COMMAND < bn.band.in > bn.band.out
>check_failure $?
>$ECHO " done"
>
>Any help would be appreciated.
>Best regards,
>Said Asma
>
>
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>
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