Band structure vs DOS bandgap

[andrei]

Hi,

I am trying to calculate band structure of certain III-V and II-VI compounds. Starting from the example of GaAs, I get a strange result that the band structure bandgap is very different from the DOS bandgap (<0.5 vs ~1.14 eV). Also, in the band structure plot zero energy (the Fermi level) falls in the conduction band. Other than that, the bands look similar to published data. It seems that I am doing something very wrong, but I just can't figure out what the problem is. The elk.in file (v 1.2.20) follows.

Thanks in advance for any hint.

andrei

tasks
  0
  10
  20

xctype
  20

avec
  1.0000 1.0000 0.0000
  1.0000 0.0000 1.0000
  0.0000 1.0000 1.0000

scale
  5.3435

sppath
  '../'

atoms
  2                                   : nspecies
  'Ga.in'                             : spfname
  1                                   : natoms
  0.00 0.00 0.00  0.0 0.0 0.0         : atposl, bfcmt
  'As.in'                             : spfname
  1                                   : natoms
  0.25 0.25 0.25  0.0 0.0 0.0         : atposl, bfcmt

ngridk
  6  6  6

vkloff
  0.5  0.5  0.5

plot1d
  3 200                                 : nvp1d, npp1d
  0.5   0.0   0.0                       : vlvp1d
  0.0   0.0   0.0
  0.5   0.5   0.0

[J. K. Dewhurst]

Hi Andrei,

The band gap for GaAs is very small at the Gamma point (I measure about 0.175 eV):

So you have to zoom into the DOS quite closely, here it is on a log scale and you can make out the spike corresponding to the dip in the band structure at Gamma:

GaAs is a tricky case because of this dip.

Cheers,
Kay.

My elk.in:

tasks
  0
  10
  20
dos
 2000 150 0
 -0.5 0.5
swidth
 0.001
xctype
  20
mixtype
  3
avec
  1.0000 1.0000 0.0000
  1.0000 0.0000 1.0000
  0.0000 1.0000 1.0000
scale
  5.3435
atoms
  2                                   : nspecies
  'Ga.in'                             : spfname
  1                                   : natoms
  0.00 0.00 0.00  0.0 0.0 0.0         : atposl, bfcmt
  'As.in'                             : spfname
  1                                   : natoms
  0.25 0.25 0.25  0.0 0.0 0.0         : atposl, bfcmt
ngridk
  16 16 16
plot1d
  3 200                                 : nvp1d, npp1d
  0.5   0.0   0.0                       : vlvp1d
  0.0   0.0   0.0
  0.5   0.5   0.0

[S. David]

Oops, didn't mean to post that last one anonymously.

[S. David]

In case it doesn't go through:
Why is the bandgap only 0.175 eV? Usually GaAs is 1.4 eV at the gamma point? Sorry for commenting on a very old thread...