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["Erik Ylvisaker" <eylvisaker@physics.ucdavis.edu>]

I think this happens because you are using shiftk 0 0 0.  Time reversal symmetry allows half the Brillouin zone to not be calculated.  But without a shift, you end up picking points like Gamma, which has no time reversed point, and points at the zone surface, whose time reversed point is separated by a reciprocal lattice vector, so it can't be eliminated by time reversal symmetry because the choice of grid didn't include it.  I think if you set shiftk to 0.5 0.5 0.5 you will see the results you expect.

 

----- Original Message -----

From: zhangtingPKU

To: forum@abinit.org

Sent: Tuesday, May 09, 2006 2:17 AM

Subject: [abinit-forum] Question about the k-point sampling in phonon calculation

Dear everyone:

     When I use ABINIT to calculate phonons,using the configurations just like the trf2_1.in, there is a mis-matching between the number of k-points in different datasets.

In the DS3(phonon at Gamma), because the keyword kptopt=2(use time-reversal symmetry), there are 112 k-points(see the attachment DS3), but in the DS4(phonon at other q point),which kptopt=3

(means no symmetry imposed), the k-points is not just the twice, but 216(also see the attachment DS4). This fact is a puzzle to me. And as a result, when I use MRGDDB code to create a uniform DDB file,

an error messege appears:

--------------------------------------------------------

   read the input derivative database number     2
   compare the current and input DDB information
   chki8 : ERROR -
    Comparing integers for variable  nkpt.
    Value from input DDB is       112 and      <----
          from transfer DDB is       216.           <----- not just twice
    Action : check your DDBs.

   leave_new : decision taken to exit ...

-------------------------------------------------------

    I'm puzzled why it happens ?