<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div><span></span><br></div> <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>I did the band structure of BN (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.<br>Normally if we change (nat = 2, ibrav = 2) to (nat = 8, ibrav = 1),we find the same nature of gap.<br>If such we have the composition B0.25Ga0.75N how we can determine the nature of gap?<br><br> Why such a problem occurs?<br><br> My input files is as following:<br><br> *With TWO ATOMS:<br><br> cat > bn.band.in << 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 < bn.band.in > bn.band.out<br> check_failure $?<br> $ECHO " done"<br><br><br><br> *and WITH 8 ATOMS:<br><br> cat > bn.band.in << EOF<br> &control<br> calculation='bands'<br> pseudo_dir = '$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 < bn.band.in > bn.band.out<br> check_failure $?<br> $ECHO " done"<br><br> Any help would be appreciated.<br> Best regards,<br> Said Asma<br><br><br><br>bests<br><br>Said Asma<br><br><br><br>________________________________<br> <br> </div> </div> </div></body></html>