Dear Said, it is not a problem, I think, as increasing the number of atoms will fold the Brillouin zone into gamma. <br><br>bests<br><br>Layla<br><br><div class="gmail_quote">2012/4/18 Said Asma <span dir="ltr"><<a href="mailto:saidasma1987@yahoo.fr">saidasma1987@yahoo.fr</a>></span><br>
<blockquote class="gmail_quote" style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div style="font-size:12pt;font-family:times new roman,new york,times,serif"> <br><div><div><div style="font-size:12pt;font-family:times new roman,new york,times,serif">
<div style="font-family:times new roman,new york,times,serif;font-size:12pt"><div style="font-family:times new roman,new york,times,serif;font-size:12pt">Dear PWScf Users,<br><br><span lang="en"><span>I did the</span> <span>band structure</span> <span>of</span> </span><span lang="en"> <span>BN</span></span><span lang="en"> <span>(zinc</span> <span>blende</span><span></span>) <span>with two</span> <span>atoms</span> <span>and I found</span> <span>a</span></span><span lang="en"><span> indirect</span></span><span lang="en"> <span>gap</span> <span></span> <span>(</span><span>like</span> <span>literature</span><span>)</span> <span>Gamma</span><span>-</span><span>X.</span> But <span>when</span> <span>I did it</span> <span>with 8</span> <span>atoms</span> <span>I found</span> <span>direct gap</span> <span>Gamma</span> -<span>Gamma</span><span></span></span>.<br>
<br>Why such a problem occurs?<br><br>My input files is as following:<br> <br> *With TWO ATOMS:<br><br>cat >
 <a href="http://bn.band.in" target="_blank">bn.band.in</a> << EOF<br> &control<br>    calculation='bands'<br>    pseudo_dir = '$PSEUDO_DIR/',<br>    outdir='$TMP_DIR/',<br>    prefix='bn'<br>
 /<br> &system<br>    ibrav=  2, celldm(1) = 6.76, nat=  2, ntyp= 2,<br>    ecutwfc = 60.0,<br>    occupations ='smearing',<br>    smearing = 'methfessel-paxton',<br>    degauss= 0.03,<br> /<br> &electrons<br>
                 conv_thr = 1.0d-7 ,<br>                 mixing_mode = 'plain' ,<br>                 mixing_beta = 0.2
 ,<br>                 diagonalization = 'david' ,<br> /<br>ATOMIC_SPECIES<br> B  10.811  B.pz-vbc.UPF<br> N  14.007  N.pz-vbc.UPF<br>ATOMIC_POSITIONS<br>  B 0.00 0.00 0.00<br>  N 0.25 0.25 0.25<br>K_POINTS {crystal_b}<br>
5<br>0.5  0.5  0.5  400<br>0    0    0    400<br>1.0  0    0    400<br>0.75 0.75 0    400<br>0    0    0    400<br>EOF<br>$ECHO "  running the band-structure calculation for bn...\c"<br>$PW_COMMAND < <a href="http://bn.band.in" target="_blank">bn.band.in</a> > bn.band.out<br>
check_failure $?<br>$ECHO " done"<br><br><br><br>*and WITH 8 ATOMS:<br><br>cat > <a href="http://bn.band.in" target="_blank">bn.band.in</a> << EOF<br>
 &control<br>
    calculation='bands'<br>
    pseudo_dir = '$PSEUDO_DIR/',<br>
    outdir='$TMP_DIR/',<br>
    prefix='bn'<br>
 /<br>
 &system<br>
    ibrav= 1, celldm(1) = 6.82, nat=8, ntyp= 2,<br>
    ecutwfc = 40.0, nbnd = 40,<br>
    occupations ='smearing',<br>
    smearing = 'methfessel-paxton',<br>
    degauss= 0.02,<br>
 /<br>
 &electrons<br>
  conv_thr =  1.0d-7,<br>
    mixing_beta = 0.2,<br>
 /<br>
<br>
ATOMIC_SPECIES<br>
 B  10.811  B.pz-vbc.UPF<br>
 N  14.007  N.pz-vbc.UPF<br>
ATOMIC_POSITIONS<br>
 B      0.000     0.000     0.000<br>
 N      0.250     0.250     0.250<br>
 B      0.000     0.500     0.500<br>
 N      0.250     0.750     0.750<br>
 B      0.500     0.500     0.000<br>
 N      0.750     0.250     0.750<br>
 B      0.500     0.000     0.500<br>
 N      0.750     0.750     0.250<br>
<br>
K_POINTS {crystal_b}<br>
4<br>
0    0    0    40<br>
0.5  0    0    40<br>
0.5  0.5  0    40<br>
0    0    0    40<br>
EOF<br>
$ECHO "  running the band-structure calculation for bn...\c"<br>
$PW_COMMAND < <a href="http://bn.band.in" target="_blank">bn.band.in</a> > bn.band.out<br>
check_failure $?<br>
$ECHO " done"<br><br>Any help would be appreciated.<br>Best regards,<br>Said Asma<br><br> </div> </div>  </div></div></div></div></div><br>_______________________________________________<br>
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<br></blockquote></div><br>