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[BOTTIN Francois <francois.bottin@cea.fr>]

Do you use Ga pseudopotential with semicore states?
Indeed, semicore effects, but also lack of numerical convergence, can be 
responsible for this difference.
See Tiago et al. PHYSICAL REVIEW B 69, 125212 (2004).
Best regards,
Francois

sankeerth rajalingam a écrit :
> 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
>
>  


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Francois Bottin                    tel: 01 69 26 41 73
CEA/DIF                            fax: 01 69 26 70 77
BP 12 Bruyeres-le-Chatel         email: Francois.Bottin@cea.fr
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