Dear Ramzi First of all, this question has been posted half a million of times...
ibrav= 2 ibrav= 1 You are changing the lattice symmetry, thus folding X into Gamma... You should be able to unfold the first Brillouin zone of the simple cubic supercell to find again the original AlAs band structure. HTH Giuseppe On Tuesday 19 June 2012 16:04:26 ramzi alaya wrote: > I did the band structure of AlAs (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. > > Why such a problem occurs? > > Thank you for your help > and advice. > > This is the > input file for the "nscf" calculation > > > With TWO ATOMS: > > > &control > > > calculation='nscf' > > > restart_mode='from_scratch', > > tstress = > .true. > > tprnfor = > .true. > > > prefix='820-28', > > pseudo_dir = > '/home/test/pseudo/', > > > outdir='/home/test/tp/' > > / > > &system > > ibrav= 2, celldm(1) =10.64, nat= 2, ntyp= 2, > > ecutwfc > =50.0, ecutrho = 200.0, nbnd =8, > > / > > &electrons > > > diagonalization='david' > > conv_thr = > 1.0e-7 > > mixing_beta > = 0.7 > > / > > ATOMIC_SPECIES > > al 26.9815 al_pz.upf > > as 74.9216 as_pz.upf > > ATOMIC_POSITIONS > > al 0.00 0.00 0.00 > > as 0.250 0.250 0.250 > > K_POINTS > > 20 > > 0.0000 0.5000 > 1.0000 1 > > 0.1000 0.5000 > 0.9000 2 > > 0.2000 > 0.5000 0.8000 3 > > 0.3000 > 0.5000 0.7000 4 > > 0.4000 > 0.5000 0.6000 5 > > 0.5000 > 0.5000 0.5000 6 > > 0.4000 > 0.4000 0.4000 7 > > 0.3000 0.3000 > 0.3000 8 > > 0.1000 > 0.1000 0.1000 9 0.0000 0.0000 > 0.0000 10 > > 0.0000 > 0.0000 0.1000 11 > > 0.0000 > 0.0000 0.2000 12 > > 0.0000 > 0.0000 0.3000 13 > > 0.0000 > 0.0000 0.4000 14 > > 0.0000 > 0.0000 0.5000 15 > > 0.0000 0.0000 0.6000 > 16 > > 0.0000 > 0.0000 0.7000 17 > > 0.0000 > 0.0000 0.8000 18 > > 0.0000 > 0.0000 0.9000 19 > > 0.0000 > 0.0000 1.0000 20 > > > > and WITH 8 ATOMS: > > > &control > > > calculation='nscf' > > > restart_mode='from_scratch', > > tstress = > .true. > > tprnfor = .true. > > prefix='820-28', > > pseudo_dir = '/home/test/pseudo/', > > outdir='/home/test/tp/' > > / > > &system > > ibrav= > 1, celldm(1) =10.64, nat= 8, > ntyp= 2, > > ecutwfc =50.0, ecutrho = 200.0, nbnd =32, > > / > > &electrons > > diagonalization='david' > > conv_thr = 1.0e-7 > > mixing_beta = 0.7 > > / > > ATOMIC_SPECIES > > al 26.9815 > al_pz.upf > > as 74.9216 > as_pz.upf > > ATOMIC_POSITIONS > > > al 0.00000000 > 0.00000000 0.00000000 > > al 0.50000000 > 0.50000000 0.00000000 > > al 0.50000000 > 0.00000000 0.50000000 > > al 0.00000000 0.50000000 > 0.50000000 > > as 0.25000000 > 0.25000000 0.25000000 > > as 0.75000000 > 0.75000000 0.25000000 > > as 0.75000000 > 0.25000000 0.75000000 > > as 0.25000000 > 0.75000000 0.75000000 > > K_POINTS > > 16 > > 0.5000 > 0.5000 0.5000 1 > > 0.4000 0.4000 > 0.4000 2 > > 0.3000 0.3000 > 0.3000 3 > > 0.2000 0.2000 > 0.2000 4 > > > > 0.1000 > 0.1000 0.1000 5 > > 0.0000 0.0000 > 0.0000 6 > > 0.0000 0.0000 > 0.1000 7 > > 0.0000 0.0000 > 0.2000 8 > > 0.0000 0.0000 > 0.3000 9 > > 0.0000 0.0000 > 0.4000 10 > > 0.0000 0.0000 > 0.5000 11 > > 0.0000 0.1000 > 0.5000 12 > > 0.0000 0.2000 > 0.5000 13 > > 0.0000 0.3000 > 0.5000 14 > > 0.0000 0.4000 > 0.5000 15 > > 0.0000 0.5000 > 0.5000 16 > > > > *********************************************************** > > Ramzi Alaya > > E-mail : ramzialaya at hotmail.fr > > Facult? des Sciences de Gab?s, Cit? Erriadh 6072 Gab?s- Tunisie > > Unit? de Recherche sur les H?t?ro-Epitaxies et Applications -- ******************************************************** - Article premier - Les hommes naissent et demeurent libres et ?gaux en droits. Les distinctions sociales ne peuvent ?tre fond?es que sur l'utilit? commune - Article 2 - Le but de toute association politique est la conservation des droits naturels et imprescriptibles de l'homme. Ces droits sont la libert?, la propri?t?, la s?ret? et la r?sistance ? l'oppression. ******************************************************** Giuseppe Mattioli CNR - ISTITUTO DI STRUTTURA DELLA MATERIA v. Salaria Km 29,300 - C.P. 10 I 00015 - Monterotondo Stazione (RM) Tel + 39 06 90672836 - Fax +39 06 90672316 E-mail: <giuseppe.mattioli at ism.cnr.it>
