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[jedokim@umich.edu]

Hi all,
I am trying to calculate the phonon band structure using rft. I have  
tried the optimization of the structure and recaculated the phonon  
dispersion and still getting negative values. I am at a loss. It may  
be I'm doing something fundamently wrong. Can anyone find anything  
wrong with the below input file? Caf_2 has an fm2m symitry FCC  
structure where primitive cell has Ca at 000 and F at 0.25 0.25 0.25  
and 0.75 0.75 0.75.


# Crystalline AlAs : computation of the phonon spectrum

   ndtset   5
#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   5.00000000E-01  0.00000000E+00  0.00000000E+00
     qpt5   5.00000000E-01  5.00000000E-01  0.00000000E+00



#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*10.4422        # This is equivalent to   10.61 10.61 10.61
    rprim    0.0  0.5  0.5
             0.5  0.5  0.5
             0.5  0.5  0.5
#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 (Ca), the second is  
of type 2 (F).

     xred   0.0  0.0  0.0
            0.25 0.25 0.25
            0.75 0.75 0.75

#Gives the number of band, explicitely (do not take the default)
#      nband  9

#Exchange-correlation functional

#     ixc   11             # LDA Teter Pade parametrization

#Definition of the planewave basis set

     ecut   100.0           # Maximal kinetic energy cut-off, in Hartree

#Definition of the k-point grid
    ngkpt   2  2  2
  nshiftk   4              # Use one copy of grid only (default)
   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

#Definition of the SCF procedure
     iscf   5          # Self-consistent calculation, using algorithm 5
    nstep   200         # Maximal number of SCF cycles
   diemac   7.0        # Although this is not mandatory, it is worth to
                       # precondition the SCF cycle. The model dielectric
                       # function used as the standard preconditioner
                       # is described in the "dielng" input variable section.
                       # The dielectric constant of AlAs is smaller  
that the one of Si (=12).