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[sankeerth rajalingam <sankeerth.rajalingam@gmail.com>]

Dear ABINIT users,

            I am a new ABINIT user. I am learning to do GW calculations to achieve correct bandgap. I have worked on basic tutorials and also band structures.
I have performed GW correction for GaAs bandstructure at the gamma point, in a way similar to the one specified in the tutorial, using Troullier-Martins pseudopotentials.

The output of the calculation, the corrected bandgap was 1.203 eV, which is significantly different from the following values:

1.58 eV, in Godby RW, Schluter M and Sham LJ, "Self-energy operators and exchange-correlation potentials in semiconductors", Phys. Rev. B. 37, 10159 (1988).

1.52eV (experimental value from TABLE 1), in Remediakis IN and Kaxiras E, “Band-structure calculations for semiconductors within generalized-density-functional theory”, Phys. Rev. B. 59, 5536 (1999).

 

Can someone please specify the reasons for the difference in the output, when compared to the value in the reference?

Also, please suggest me if I need to make any changes in the input file.

 

-------------------------INPUT FILE BEGINS---------------------------

The input file used for the calculation is shown below.

ndtset      4

 shiftk2  0.0 0.0 0.0  # This grid contains the Gamma point
             0.0 0.5 0.5
             0.5 0.0 0.5
             0.5 0.5 0.0
istwfk2  19*1                    # Option needed for Gamma
iscf2    -2             # Non self-consistent calculation
getden2  -1             # Read previous density file
nband2   9
nbandkss2 100        # Number of bands to store in KSS file

# Dataset3: Calculation of the screening (epsilon^-1 matrix)
optdriver3  3        # Screening calculation
getkss3     -1       # Obtain KSS file from previous dataset
nband3       150      # Bands to be used in the screening calculation
ecutwfn3     5     # Planewaves to be used to represent the wavefunctions
ecuteps3     7     # Dimension of the screening matrix
ppmfrq3    16.7 eV  # Imaginary frequency where to calculate the screening

# Dataset4: Calculation of the Self-Energy matrix elements (GW corrections)
optdriver4  4        # Self-Energy calculation
getkss4     -2       # Obtain KSS file from dataset 1
getscr4     -1       # Obtain SCR file from previous dataset
nband4      200      # Bands to be used in the Self-Energy calculation
ecutwfn4    6      # Planewaves to be used to represent the wavefunctions
ecutsigx4   7      # Dimension of the G sum in Sigma_x
                     # (the dimension in Sigma_c is controlled by npweps)
nkptgw4      1                # number of k-point where to calculate the GW correction
kptgw4                       # k-points
  0.000    0.000    0.000    # (Gamma)
bdgw4       4  5             # calculate GW corrections for bands from 4 to 5


# Definition of the unit cell: fcc
acell  3*10.683187931        # This is equivalent to   10.217 10.217 10.217
rprim  0.0  0.5  0.5   # FCC primitive vectors (to be scaled by acell)
          0.5  0.0  0.5
          0.5  0.5  0.0

# Definition of the atom types
ntypat 2          # There is only one type of atom
znucl 31 33          # The keyword "znucl" refers to the atomic number of the
                  # possible type(s) of atom. The pseudopotential(s)
                  # mentioned in the "files" file must correspond
                  # to the type(s) of atom. Here, the only type is Silicon.

# Definition of the atoms
natom 2           # There are two atoms
typat  1 2        # They both are of type 1, that is, Silicon.
xred              # Reduced coordinate of atoms
      0.0  0.0  0.0
      0.25 0.25 0.25

# Definition of the planewave basis set (at convergence 16 Rydberg 8 Hartree)
ecut 8.0          # Maximal kinetic energy cut-off, in Hartree

# Use only symmorphic operations
symmorphi 0

# Definition of the SCF procedure
nstep   10        # Maximal number of SCF cycles
diemac  12.0      # Although this is not mandatory, it is worth to
                  # precondition the SCF cycle. The model dielectric
                  # function used as the standard preconditioner
                  # is described in the "dielng" input variable section.
                  # Here, we follow the prescription for bulk silicon.
tolwfr  1.0d-10

# This line added when defaults were changed (v5.3) to keep the previous, old behaviour
  iscf 5

------------------------------INPUT FILE ENDS--------------------------

 

 

----------------------------OUTPUT FILE BEGINS-----------------------

The output of the calculation is shown below.

 k =    0.000   0.000   0.000

  Band   E0   <VxcLDA>  SigX  SigC(E0)   Z    dSigC/dE  Sig(E)  E-E0       E
    4  -0.428 -11.190 -12.443   0.749   0.771  -0.298 -11.578  -0.389  -0.816
    5   0.216 -10.251  -7.238  -2.794   0.784  -0.275 -10.080   0.171   0.387

 E^0_gap          0.643
 E^GW_gap         1.203
 DeltaE^GW_gap    0.560

--------------------------------OUTPUT FILE ENDS-------------------------

 

 Thank you.

 Regards,
 Sankeerth Rajalingam
 Graduate Research Assistant