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[Igor Lukacevic <ilukacevic@fizika.unios.hr>]

Dear colleagues,

I am having problems in reproducing the phonon dispersions in the rocksalt phase of ZrO2 wrt the results obtained in F. Detraux et al., prl 81, 3297 (1998):

1] I obtain many imaginary frequencies.
2] Acoustic mode(s) go imaginary, while the optical mode is the unstable one.

They have been using ecut 30 Ha and ngkpt 3*4, while I used ecut 60 Ha and ngkpt 3*6. Both psuedos have the same number of valence electrons.

I'm using abinit 5.8.4p, and I correct the output of mrgdbb (acell and rprim) to be able to use brav=2 option in anaddb. My calcs converge without warnings. I'm sending the inputs and the plot bellow.

Could anyone give me a clue why this happens and how to improve my calcs?

Thank you all in advance!

Yours,

Igor Lukacevic



==================================
RF phonon input

# Crystalline ZrO2 - fluorite - cubic fcc - Fm-3m #225 : computation of the phonon spectrum

   ndtset   18
#Set 1 : ground state self-consistency

  getwfk1   0            # Cancel default
  kptopt1   1            # Automatic generation of k points, taking
                         # into account the symmetry
    nqpt1   0            # Cancel default
  tolvrs1   1.0d-18      # SCF stopping criterion (modify default)
  rfphon1   0            # Cancel default

#Q vectors for all datasets

#Complete set of symmetry-inequivalent qpt chosen to be commensurate
# with kpt mesh so that only one set of GS wave functions is needed.
#Generated automatically by running GS calculation with kptopt=1,
# nshift=0, shiftk=0 0 0 (to include gamma) and taking output kpt set
# file as qpt set. Set nstep=1 so only one iteration runs.

     nqpt   1            # One qpt for each dataset (only 0 or 1 allowed)
                         # This is the default for all datasets and must
                         #  be explicitly turned off for dataset 1.

     qpt2   0.00000000E+00  0.00000000E+00  0.00000000E+00
     qpt3   0.00000000E+00  0.00000000E+00  0.00000000E+00
     qpt4   1.66666667E-01  0.00000000E+00  0.00000000E+00
     qpt5   3.33333333E-01  0.00000000E+00  0.00000000E+00
     qpt6   5.00000000E-01  0.00000000E+00  0.00000000E+00
     qpt7   1.66666667E-01  1.66666667E-01  0.00000000E+00
     qpt8   3.33333333E-01  1.66666667E-01  0.00000000E+00
     qpt9   5.00000000E-01  1.66666667E-01  0.00000000E+00
     qpt10 -3.33333333E-01  1.66666667E-01  0.00000000E+00
     qpt11 -1.66666667E-01  1.66666667E-01  0.00000000E+00
     qpt12  3.33333333E-01  3.33333333E-01  0.00000000E+00
     qpt13  5.00000000E-01  3.33333333E-01  0.00000000E+00
     qpt14 -3.33333333E-01  3.33333333E-01  0.00000000E+00
     qpt15  5.00000000E-01  5.00000000E-01  0.00000000E+00
     qpt16  5.00000000E-01  3.33333333E-01  1.66666667E-01
     qpt17 -3.33333333E-01  3.33333333E-01  1.66666667E-01
     qpt18 -3.33333333E-01  5.00000000E-01  1.66666667E-01

#Set 2 : Response function calculation of d/dk wave function

    iscf2   -3         # Need this non-self-consistent option for d/dk
  kptopt2   2          # Modify default to use time-reversal symmetry
  rfphon2   0          # Cancel default
  rfelfd2   2          # Calculate d/dk wave function only
  tolvrs2   0.0        # Cancel default for d/dk
  tolwfr2   1.0d-22    # Use wave function residual criterion instead

#Set 3 : Response function calculation of Q=0 phonons and electric field pert.

  getddk3   2          # d/dk wave functions from last dataset
  kptopt3   2          # Modify default to use time-reversal symmetry
  rfelfd3   3          # Electric-field perturbation response only

#Sets 4-17 : Finite-wave-vector phonon calculations (defaults for all datasets)

   getwfk   1          # Use GS wave functions from dataset1
   kptopt   3          # Need full k-point set for finite-Q response
   rfphon   1          # Do phonon response
  rfatpol   1 3        # Treat displacements of all atoms
    rfdir   1 1 1      # Do all directions (symmetry will be used)
   tolvrs   1.0d-8     # This default is active for sets 3-10

#######################################################################
#Common input variables

#Definition of the unit cell
    acell   3*9.46
   angdeg   90  90  90
   brvltt  -1
  spgroup   225

#Definition of the atom types
   ntypat   2
    znucl   40 8 8

#Definition of the atoms
    natom   3
    typat   1 2 2

     xred   0.00  0.00  0.00
            0.25  0.25  0.25
            0.75  0.75  0.75

#Gives the number of band, explicitely (do not take the default)
    nband   14

#Exchange-correlation functional

      ixc   3

#Definition of the planewave basis set

     ecut   60

#Definition of the k-point grid
  nshiftk   4
  shiftk    0.5  0.5  0.5
            0.5  0.0  0.0
            0.0  0.5  0.0
            0.0  0.0  0.5
  ngkpt     3*6

#Definition of the SCF procedure
    iscf    7              # Use Pulay mixing sheme for SCF cycle
npulayit    10             # Number of Pulay iterations
  nnsclo    4              # Number of non-self consistent loops
   nline    8              # Number of line minimisations

  diemac    4


==================================
anaddb input

!Input file for the anaddb code. Analysis of the SiO2 DDB                      

!Flags
 ifcflag   1     ! Interatomic force constant flag

!Wavevector grid number 1 (coarse grid, from DDB)
  brav    2      ! Bravais Lattice : 1-S.C., 2-F.C., 3-B.C., 4-Hex.)
  ngqpt   3*6    ! Monkhorst-Pack indices
  nqshft  1      ! number of q-points in repeated basic q-cell
  q1shft  3*0.0

!Effective charges
     asr   1     ! Acoustic Sum Rule. 1 => imposed asymetrically
  chneut   1     ! Charge neutrality requirement for effective charges.

!Interatomic force constant info
  dipdip  1      ! Dipole-dipole interaction treatment

!Phonon band structure output for band2eps - See note near end for
! dealing with gamma LO-TO splitting issue.
   eivec  4

!Wavevector list number 1 (Reduced coordinates and normalization factor)        
  nph1l   71     ! number of phonons in list 1                            

  qph1l   0.0000  0.0000  0.0000   1.0    !(gamma point)
          0.0375  0.0375  0.0750   1.0
          0.0750  0.0750  0.1500   1.0
          0.1125  0.1125  0.2250   1.0
          0.1500  0.1500  0.3000   1.0
          0.1875  0.1875  0.3750   1.0
          0.2250  0.2250  0.4500   1.0
          0.2625  0.2625  0.5250   1.0
          0.3000  0.3000  0.6000   1.0
          0.3375  0.3375  0.6750   1.0
          0.3750  0.3750  0.7500   1.0    !(K point)
          0.3875  0.3875  0.7750   1.0
          0.4000  0.4000  0.8000   1.0
          0.4125  0.4125  0.8250   1.0
          0.4250  0.4250  0.8500   1.0
          0.4375  0.4375  0.8750   1.0
          0.4500  0.4500  0.9000   1.0
          0.4625  0.4625  0.9250   1.0
          0.4750  0.4750  0.9500   1.0
          0.4875  0.4875  0.9750   1.0
          0.5000  0.5000  1.0000   1.0    !(X point)
          0.5500  0.5500  1.0000   1.0
          0.6000  0.6000  1.0000   1.0
          0.6500  0.6500  1.0000   1.0
          0.7000  0.7000  1.0000   1.0
          0.7500  0.7500  1.0000   1.0
          0.8000  0.8000  1.0000   1.0
          0.8500  0.8500  1.0000   1.0
          0.9000  0.9000  1.0000   1.0
          0.9500  0.9500  1.0000   1.0
          1.0000  1.0000  1.0000   1.0    !(gamma point)
          0.9500  0.9500  0.9500   1.0
          0.9000  0.9000  0.9000   1.0
          0.8500  0.8500  0.8500   1.0
          0.8000  0.8000  0.8000   1.0
          0.7500  0.7500  0.7500   1.0
          0.7000  0.7000  0.7000   1.0
          0.6500  0.6500  0.6500   1.0
          0.6000  0.6000  0.6000   1.0
          0.5500  0.5500  0.5500   1.0
          0.5000  0.5000  0.5000   1.0    !(L point)
          0.5000  0.4500  0.5000   1.0
          0.5000  0.4000  0.5000   1.0
          0.5000  0.3500  0.5000   1.0
          0.5000  0.3000  0.5000   1.0
          0.5000  0.2500  0.5000   1.0
          0.5000  0.2000  0.5000   1.0
          0.5000  0.1500  0.5000   1.0
          0.5000  0.1000  0.5000   1.0
          0.5000  0.0500  0.5000   1.0
          0.5000  0.0000  0.5000   1.0    !(X point)
          0.5000  0.0250  0.5250   1.0
          0.5000  0.0500  0.5500   1.0
          0.5000  0.0750  0.5750   1.0
          0.5000  0.1000  0.6000   1.0
          0.5000  0.1250  0.6250   1.0
          0.5000  0.1500  0.6500   1.0
          0.5000  0.1750  0.6750   1.0
          0.5000  0.2000  0.7000   1.0
          0.5000  0.2250  0.7250   1.0
          0.5000  0.2500  0.7500   1.0    !(W point)
          0.5000  0.2750  0.7250   1.0
          0.5000  0.3000  0.7000   1.0
          0.5000  0.3250  0.6750   1.0
          0.5000  0.3500  0.6500   1.0
          0.5000  0.3750  0.6250   1.0
          0.5000  0.4000  0.6000   1.0
          0.5000  0.4250  0.5750   1.0
          0.5000  0.4500  0.5500   1.0
          0.5000  0.4750  0.5250   1.0
          0.5000  0.5000  0.5000   1.0    !(L point)

!Wavevector list number 2 (Cartesian directions for non-analytic gamma phonons)

!The output for this calculation must be cut-and-pasted into the
! t59_out.freq file to be used as band2eps input to get proper LO-TO
! splitting at gamma.  Note that gamma occurrs twice.

  nph2l    1       ! number of directions in list 2

  qph2l   1.0  0.0  0.0    0.0
# This line added when defaults were changed (v5.3) to keep the previous, old behaviour
  symdynmat 0