Bandgap of Si in GW

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Revision as of 16:06, 7 June 2012 by Vaspmaster (talk | contribs)

Description: calculation of the bandgap of Si using various flavours of GW.


To do GW calculations we have to follow a 3-step procedure.

Step 1: a DFT groundstate calculation

Everything starts with a standard DFT groundstate calculation (in this case PBE).

  • INCAR
ISMEAR =  0
SIGMA  =  0.05
GGA    = PE
  • KPOINTS
6x6x6
 0
G
 6 6 6
 0 0 0
  • POSCAR
system Si
5.430
0.5 0.5 0.0
0.0 0.5 0.5
0.5 0.0 0.5
2
cart
0.00 0.00 0.00
0.25 0.25 0.25

Step: obtain DFT virtual orbitals

To obtain a WAVECAR file with a reasonable number of virtual orbitals (50-100 per atom) we need to restart from the previous groundstate calculation with ALGO=Exact, and manually set the number of bands by means of the NBANDS-tag. To obtain the corresponding WAVEDAR file we additionally specify LOPTICS=.TRUE.

  • INCAR
ALGO = Exact
NBANDS  = 64
LOPTICS = .TRUE.
NEDOS = 2000
## you might try
#LPEAD = .TRUE.

ISMEAR =  0
SIGMA  =  0.05
GGA    = PE


Step 3:

To quickly find the QP-energy of the highest lying occupied state, try

grep "     4     " OUTCAR | sort -n -k 3 | tail -1 | awk '{print $3}'

and for the lowest lying unoccupied state,

grep "     5     " OUTCAR | sort -n -k 3 | head -1 | awk '{print $3}'

Download

Si_bandgap_GW.tgz


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