[Pw_forum] (no subject)

[Layla Martin-Samos]

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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