The ABINIT Users Mailing List ( CLOSED )

[matthieu verstraete <matthieu.jean.verstraete@gmail.com>]

at first sight your number of bands in the kss file should be >= those
used in the following dtsets. ABINIT should even complain...

in general you can expect 0.1eV accuracy, not better (and not always
0.06 like in GSS)

have you converged all your parameters, or are you just using those from 
Godby?

And have you checked that in GSS they are doing strict GW, with no
vertex corrections, model screening functions, and are they using the
same plasmon pole as you?

GaAs can be quite delicate: there are spin orbit splittings at Gamma,
and a bunch of bands lying around. Check the precision of your LDA
band structure wrt the literature first.

Matthieu

On Fri, Sep 25, 2009 at 10:33 PM, sankeerth rajalingam
<sankeerth.rajalingam@gmail.com> wrote:
>
> 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
>
>
>



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. Matthieu Verstraete

NEW PHONE NUMBER

Universite de Liège
Institut de Physique, Bat. B5, 3/7
Allée du 6 aout, 17
B- 4000 Sart Tilman, Liège
Belgium

Phone : +32 4 366 90 17
Fax   : +32 4 366 36 29

Mail : matthieu.jean.verstraete@gmail.com