Dear Said, It is not an error. When you enlarge the primitive cell, the brillouin zone gets smaller. Moreover, some high symmetric points might be overlapped with Gamma, for the symmetry is changed (ibrav changes). This effect is called brillouin zone folding.
Plato Tao -----Original Messages----- From: "Said Asma" <[email protected]> Sent Time: Thursday, April 26, 2012 To: "giannozz at democritos.it" <giannozz at democritos.it>, "pw_forum at pwscf.org" <pw_forum at pwscf.org> Cc: Subject: [Pw_forum] Error band structure Dear Giannozzi , 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. Normally if we change (nat = 2, ibrav = 2) to (nat = 8, ibrav = 1),we find the same nature of gap (the unit cell has changedtosimplecubic). If such we have the composition B0.25Ga0.75N how we can determine the nature of gap? 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 bests Said Asma ________________________________ -- ------------------------------------------------------------------- PH.D. candidate Peng Tao Magnetism and Magnetic Materials Division National Laboratory for Material Science Institute of Metal Research, Chinese Academy of Sciences Phone +86-024-83978751 ------------------------------------------------------------------- -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20120428/c83c78eb/attachment.htm
