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[<gaotaoscu@hotmail.com>]

Dear All,
 
When I try to reproduce the TO-LO splitting for CaF2 (original paper: PHYSICAL
REVIEW B vol68, 195123,2003),I got no LO-TO splitting in my calculation.
According to the experiments and the theoretical calculation, there should 
have
a TO-LO splitting in Gamma point for CaF2, but my input file is not able to 
let
these kind of slitting. my version is abinit-5.4.4p, and pseudopotential is
'20ca.pspnc' and '9f.pspnc'. Below is my setting for the DDB and phonon parts,
and the related output, any comments or suggestion is appreciated.

1,Generation of the derivative databases,
# Crystalline CaF2 : computation of the phonon spectrum

   ndtset   10
  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

     nqpt   1            # One qpt for each dataset (only 0 or 1 allowed)

     qpt2   0.00000000E+00  0.00000000E+00  0.00000000E+00
     qpt3   0.00000000E+00  0.00000000E+00  0.00000000E+00
     qpt4   2.50000000E-01  0.00000000E+00  0.00000000E+00
     qpt5   5.00000000E-01  0.00000000E+00  0.00000000E+00
     qpt6   2.50000000E-01  2.50000000E-01  0.00000000E+00
     qpt7   5.00000000E-01  2.50000000E-01  0.00000000E+00
     qpt8  -2.50000000E-01  2.50000000E-01  0.00000000E+00
     qpt9   5.00000000E-01  5.00000000E-01  0.00000000E+00
     qpt10 -2.50000000E-01  5.00000000E-01  2.50000000E-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 4-10 : 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*10.3232         # This is equivalent to   10.61 10.61 10.61
    rprim   0.0  0.5  0.5   # In lessons 1 and 2, these primitive vectors 
            0.5  0.0  0.5   # (to be scaled by acell) were 1 0 0  0 1 0  0 0 
1 
            0.5  0.5  0.0   # that is, the default.

#Definition of the atom types
   ntypat   2         # There are two types of atom
    znucl   20 9     # 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, type 1 is the Aluminum,
                      # type 2 is the Arsenic.

#Definition of the atoms
    natom   3         # There are two atoms
    typat   1 2 2       # The first is of type 1 (Al), the second is of type 2
(As).
    xred                      # will follow, one triplet of number for each
atom
         0.0  0.0  0.0      # Triplet giving the REDUCED coordinate of atom 1.
         1/4  1/4  1/4      # Triplet giving the REDUCED coordinate of atom 2.
         3/4  3/4  3/4               # Note the use of fractions (remember the
limited 
 
#Gives the number of band, explicitely (do not take the default)
    nband   11         
    occopt  3
#Exchange-correlation functional

      ixc   1             # LDA Teter Pade parametrization

#Definition of the planewave basis set

     ecut   26.0           # Maximal kinetic energy cut-off, in Hartree

#Definition of the k-point grid
    ngkpt   4  4  4          
  nshiftk   4              # Use one copy of grid only (default)
   shiftk   0.0 0.0 0.5    # This gives the usual fcc Monkhorst-Pack grid
            0.0 0.5 0.0
            0.5 0.0 0.0
            0.5 0.5 0.5

#Definition of the SCF procedure
    iscf     7        # Self-consistent calculation, using algorithm 5
    nstep   1500      # Maximal number of SCF cycles
    diemac   9.0      # Although this is not mandatory, it is worth to
                      # precondition the SCF cycle. The model dielectric

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
2,computation of phonon band structures 

!Input file for the ifc code. Analysis of the CaF2 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   4  4  4   ! 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    80      ! number of phonons in list 1                             

  qph1l       0.00000000E+00  0.00000000E+00  0.00000000E+00  1.0
              5.00000000E-02  2.50000000E-02  2.50000000E-02  1.0
              1.00000000E-01  5.00000000E-02  5.00000000E-02  1.0
                  .........................................
              5.00000000E-01  4.50000000E-01  5.50000000E-01  1.0 
              5.00000000E-01  4.75000000E-01  5.25000000E-01  1.0
              5.00000000E-01  5.00000000E-01  5.00000000E-01  1.0

!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
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
3, output of LO-TO splitting.
     ........................................................
 Treat the second list of vectors
-begin at tcpu      0.470  and twall      0.957 sec
  Phonon at Gamma, with non-analyticity in the
  direction (cartesian coordinates)  1.00000  0.00000  0.00000
 Phonon energies in Hartree :
   0.000000E+00  0.000000E+00  0.000000E+00  1.634493E-03  1.634494E-03
   1.634498E-03  1.962988E-03  1.962988E-03  1.962990E-03
 Phonon frequencies in cm-1    :
-  0.000000E+00  0.000000E+00  0.000000E+00  3.587298E+02  3.587300E+02
-  3.587309E+02  4.308260E+02  4.308260E+02  4.308265E+02
+Total cpu time      0.470  and wall time      0.959 sec
 anaddb : the run completed succesfully.

Regards,

Tao