[Pw_forum] Fw: band structure issue

[Tariq Sami]

     On Thursday, January 14, 2016 3:49 PM, Tariq Sami <tariq.sami72 at yahoo.com> wrote:
 

 
Hello dear QE users,  I'm using Quantum espresso-5.2.0 for the calculation of band structure of rutile TiO2. While doing my calculations for single cell using


&control
 calculation = 'scf',
 prefix = 'tio',
 verbosity = 'default',
 outdir = './' ,
 pseudo_dir = '/home/sami_QU/espresso-5.2.0/pseudo',

 /
 &system
 ibrav = 6,
 celldm(1) = 8.680890966,
 celldm(3) = 0.64394729330137,
 nat = 6,
 ntyp = 2,
 ecutwfc = 40,
 ecutrho = 300,
 occupations = 'tetrahedra',
 smearing ='mp',
 degauss= 0.02 ,
 /
 &electrons
 conv_thr = 1.0e-09,
 electron_maxstep = 100,
 mixing_beta = 0.3,
 conv_thr = 1.0e-08,
 mixing_mode = 'plain',
 /

 ATOMIC_SPECIES
 O 15.999 O.pz-nc.UPF
 Ti 47.867 Ti.pz-n-nc.UPF
 ATOMIC_POSITIONS (alat)
 Ti 0.00000000 0.00000000 0.00000000
Ti 0.50000000 0.50000000 0.32197370
 O 0.30530000 0.30530000 0.00000000
 O -0.30530000 -0.30530000 0.00000000
 O 0.80530010 0.19470000 0.32197370
 O 0.19470000 0.80530010 0.32192370
 K_POINTS (automatic)
 3 3 6 1 1 1
my results are some what consistent with the previous studies ,but when i do the same calculations for 2x2x2 supercell using 
 / 
&system
 ibrav = 6,
 celldm(1) = 17.36178193,
 celldm(3) = 0.64394729330137,
 nat = 48,
 ntyp = 2,
 ecutwfc = 40,
 ecutrho = 300,
 occupations = 'tetrahedra',
 smearing ='mp',
 degauss= 0.02 ,
 /
 &electrons
 conv_thr = 1.0e-09,
 electron_maxstep = 100,
 mixing_beta = 0.3,
 conv_thr = 1.0e-08,
 mixing_mode = 'plain',
 /

 ATOMIC_SPECIES
 O 15.999 O.pz-nc.UPF
 Ti 47.867 Ti.pz-n-nc.UPF
 ATOMIC_POSITIONS (alat)
 Ti 0.00000000 0.00000000 0.00000000
 Ti 0.25000000 0.25000000 0.16098685
 O 0.15265000 0.15265000 0.00000000
 O -0.15265000 -0.15265000 0.00000000
 O 0.40265005 0.09735000 0.16986850
 O 0.09735000 0.40265005 0.16986850
 Ti 0.50000000 0.00000000 0.00000000
 Ti 0.75000000 0.25000000 0.16098685
 O 0.65265000 0.15265000 0.00000000
 O 0.34735000 -0.15265000 0.00000000
 O 0.90265005 0.09735000 0.16986850
 O 0.59735000 0.40265005 0.16986850
 Ti 0.00000000 0.50000000 0.00000000
 Ti 0.25000000 0.75000000 0.16098685
 O 0.15265000 0.65265000 0.00000000
 O -0.15265000 0.34735000 0.00000000
 O 0.40265005 0.59735000 0.16986850
 O 0.09735000 0.90265005 0.16986850
 Ti 0.50000000 0.50000000 0.00000000
 Ti 0.75000000 0.75000000 0.16098685
 O 0.65265000 0.65265000 0.00000000
 O 0.34735000 0.34735000 0.00000000
 O 0.90265005 0.59735000 0.16986850
 O 0.59735000 0.90265005 0.16986850
 Ti 0.00000000 0.00000000 0.32197370
 Ti 0.25000000 0.25000000 0.48296055
 O 0.15265000 0.15265000 0.32197370
 O -0.15265000 -0.15265000 0.32197370
 O 0.40265005 0.09735000 0.48296055
 O 0.09735000 0.40265005 0.48296055
 Ti 0.50000000 0.00000000 0.32197370
 Ti 0.75000000 0.25000000 0.48296055
 O 0.65265000 0.15265000 0.32197370
 O 0.34735000 -0.15265000 0.32197370
 O 0.90265005 0.09735000 0.48296055
 O 0.59735000 0.40265005 0.48296055
 Ti 0.00000000 0.50000000 0.32197370
 Ti 0.25000000 0.75000000 0.48296055
 O 0.15265000 0.65265000 0.32197370
 O -0.15265000 0.34735000 0.32197370
 O 0.40265005 0.59735000 0.48296055
 O 0.09735000 0.90265005 0.48296055
 Ti 0.50000000 0.50000000 0.32197370
 Ti 0.75000000 0.75000000 0.48296055
 O 0.65265000 0.65265000 0.32197370
 O 0.34735000 0.34735000 0.32197370
 O 0.90265005 0.59735000 0.48296055
 O 0.59735000 0.90265005 0.48296055

 K_POINTS (automatic)
 3 3 6 1 1 1
 

there are some extra states , as in Fig[1]. The same test calculations when done using siesta gives accurate results Fig. [2].A comparison of Dos of the cell and supercell using siesta and Qe respectively is shown in the Fig[3]. Actually i'm a new QE user , so can anyone please help me out in this regardI look forward to your suggestion! Thank you! 
SAMI TARIQ 
MPHILL CANDIDATE
DEPARTMENT OF PHYSICS
QUAID E AZAM UNIVERSITY, ISLAMABAD
PAKISTAN 


   
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