[Pw_forum] Default value of nbnd for GaAs

[Mohammad Abu Raihan Miah]

Hi all,

I am currently doing simulation to calculate the band structure of GaAs. I
use the basic primitive cell to simulate.

In order to calculate the band structure I need to specify the number of
bands, nbnd parameter. Now as far as I understand, For GaAs there are 4
valence electrons per atom. So for a 2 atom primitive cell, the default
value of nbnd should be 4. But instead I get the default value of nbnd as 9
(I checked the value from output file as for each k, 9 eigen energy value
is calculated)

My input file as follows:


&CONTROL
  calculation='scf',
  outdir='out_bulk',
  prefix='GaAs_2',
  pseudo_dir='.',
  verbosity='low',
  tstress=.false.,
  tprnfor=.false.,
/

&SYSTEM
  ibrav=2,
  celldm(1)=10.6839445905d0,
  nat=2,
  ntyp=2,
  ecutwfc=50.0d0,
  ecutrho=400.0d0,
  input_dft='PBE',
/

&ELECTRONS
  diagonalization='david',
  conv_thr=1d-06,
  mixing_mode='plain',
  mixing_beta=0.700d0,
/

ATOMIC_SPECIES
  As 74.921600d0 As.pbe-n-rrkjus_psl.0.2.UPF
  Ga 69.723000d0 Ga.pbe-dn-rrkjus_psl.0.2.UPF

ATOMIC_POSITIONS {alat}
  Ga   0.0000000000d0   0.0000000000d0   0.0000000000d0
  As   0.2500000000d0   0.2500000000d0   0.2500000000d0

K_POINTS {automatic}
  8 8 8 0 0 0


Could anyone please explain that to me?

Thank you very much.

Best,
-- 
Mohammad Abu Raihan Miah
PhD Student
Department of Electrical and Computer Engineering (ECE)
<http://www.ece.ucsd.edu/>
University of California, San Diego <http://www.ucsd.edu/>
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