The ABINIT Users Mailing List ( CLOSED )

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

> Dear All
>
> I've tried to perform the GW corrections for GaP band structue. My
> platform is Fedora 8.0 running on an Intel Core 2 Quad CPU with 4 Gb
> of RAM. I firstly calculated the ground state density and the KSS file,
> by using the parallelized Abinit 5.4.4(MPI version, prepared for a
> x86_64_linux) and the Abinit 5.4.4(sequential version, prepared for a
> x86_64_
> linux), respectively. Both calculations were successfully completed.
>
> However, when I carried out the screening calculation using the
> parallelized
> Abinit 5.4.4 with the pre-calculated KSS file, the program seemed to
> terminate
> within the screening main loop at the start of the "cchi0" calculation of
> the
> q point number 2. The error message at the end of the log file is as
> follows.
> The
> complete input and log files are listed below. (sorry if it's very
> lengthy)
>
> ....................................................................
> cchi0 : enter
>
>   use symmetries    =          0
>   use time reversal =  F
>   spectral method   =          0
>  calculating chi0(q,omega,G,G")
>
>
>  cchi0 : reading wavefunctions from file
>   trying to allocate wavefunctions in real space
>   allocated
>  cchi0 : real space wavefunctions are now in memory
>
>  calculation status (  865 to be completed) :
>  cchi0 : ik =    1 /    865   is =  1  done by processor      0
>  cchi0 : ik =    2 /    865   is =  1  done by processor      0
>
>  cchi0 : ERROR -
>   kp=k-q-G0 not found
>  ik =  3 k =     0.166667    0.166667    0.083333
>  k-q =                 0.250000    0.333333    0.083333
> -P-0000
> -P-0000  leave_new : decision taken to exit ...
> ......................................................................
>


 Dear Thanusit Burinprakhon

 The difference between k-q and k should be a reciprocal lattice vector.
 In your case the first two reduced components of k and k-q
 do not cancel each other. I think the problem is in the k-mesh
 used to generate the KSS file.

 Can you check if the errors shows up also if the k-mesh is specified
 using the "standard" procedure, namely using ngkpt and nshiftk and shiftk.
 You might try the values used in the GW tutorial for silicon:

# Dataset2: calculation of kss file
# Definition of k-points

 ngkpt2  4 4 4 (or 6 6 6)
 nshiftk2  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

 You have to run these tests only to check if abinit finds
 all the points it needs, so you can safely decrease
 ecutwfn, ecuteps and .nbands during the tests.

>
> I also have another question on the screening issue. Does Abinit need the
> k-point
> grid for screening calculations?

 Of course, the k-grid is the same as the mesh used to generate the KSS file.
 The dielectric matrix is calculated for a set of q-points that are given
 by all the possible difference between two k-points (taking into account
symmetries)

 Hope this helps
 Regards
 Matteo Giantomassi