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

[Layla Martin-Samos]

Dear Said, I have not a big experience in crystals but as long as I
understand, the "nature" of the gap is defined by its "nature" calculated
with the unit cell of your crystal. If instead of the unit cell you are
using bigger cells then you need to make a careful analysis of the
symmetries to unfold your brilloin zone by hand. When you use dopants, is
the same mechanism. To be safe and avoid manual unfoldings, you need to
build the unit cell corresponding to B0.25Ga075N. I have no idea of what is
the unit cell for your system. Maybe you can find more info in
crystallographic tables.

best regards

Layla

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

> 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 aindirect
> gap  (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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