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["Matteo Giantomassi" <Matteo.Giantomassi@uclouvain.be>]

> Dear all,
>
> I encounter a problem in GW "band structure" calculations (abinit5.5.4,
> parallel).
>
> When I calculate GW correction values for titanium nitride, I cannot
> calculate
> the corrections at my own choice of k-points.
>
> Is it possible to chose for explicit k-points in GW?

Directly from the tutorial that, for sure, you read carefully ;-)

nkptgw tells the number of k-points for which the GW corrections must be
computed. The k-points coordinates are given in kptgw. At present, they
MUST belong to the k-point grid chosen to generate the KSS file. Hence if
you wish the GW correction in a particular k-point, you should choose a
grid containing it. Usually this is done by taking the k-point grid where
the convergence is achieved and shifting it such as at least one k-point
is placed on the wished position in the Brillouin zone. bdgw gives the
minimum/maximum band whose energies are calculated for the given k-point.









> I am especially interested in the excluded kptgw's in the input file
> below.
>
> The output -if one of the excluded kptgw's is taken - exits with
>
>  findk : check if the k-points for sigma are in the set of BZ
>
>  findk : ERROR -
>  k-point  0.500  0.750        0.250  not in the set of kbz
> -P-0000
> -P-0000  leave_new : decision taken to exit ...
>
> Many thanks in advance
> Rolf Oettking
>
> Attachment: The input file reads
>
> # Crystalline Titanium Nitride :
> # calculation of the quasi-particle Fermi energy
>
> #Parameters for the GW calculation
> optdriver    4
> nband     30
> ecutsigx    6.5
> ecutwfn     6.5
>
> gwcalctyp   12
>
> nkptgw             4
> kptgw
>   0.000  0.000        0.000 # Gamma point
>   0.500  0.500        0.000 # X point
> #  0.500  0.750  0.250 # W point
>   0.375  0.750        0.375 # K point
>   0.000  0.000        0.000 # Gamma point
> #  0.500  0.500  0.500 # L point
> #  0.500  0.750  0.250 # W point
> #  1.000  1.000  0.000 # Gamma'
>
> bdgw
>   5 10
>   5 10
>   5 10
>   5 10
>   5 10
>   5 10
>   5 10
> #  5 10
>
> #Definition of occupation numbers
> occopt 3
> tsmear 0.05
>
> #Definition of the unit cell
> acell  8.3641814936E+00  8.3641814936E+00  8.3641814936E+00 Bohr
>
> 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
> znucl 22 7
>
> #Definition of the atoms
> natom 1
> typat 1 2
> xred
>    0.0        0.0  0.0
>    1/2        1/2  1/2
>
> #Definition of the planewave basis set
> ecut  8.0
>
> #Definition of the k-point grid
> kptopt              3
> ngkpt       8 8 8
> nshiftk       1
> shiftk              0.  0.  0.
> istwfk              512*1
>
> #Definition of the SCF procedure
> nstep 50
>
> toldfe 1.0d-8
>
> prtvol           5
> enunit           1
>