# Crystalline BaTiO3: computation of the phonon spectrum

   ndtset   3

#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
 
#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

#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

#Common sttings

   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 5        # 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


#Definition of the k-point grid
ngkpt  8 8 8
nshiftk 1
shiftk 0.5 0.5 0.5

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

#Definition of the unit cell
   acell 3*7.5323692530
   rprim  1 0 0
          0 1 0
          0 0 1

#Definition of the atom types
   ntypat 3
    znucl 56 22 8

#Definition of the atoms
natom 5
typat 1*1 1*2 3*3
xred
  0.0 0.0 0.0
  0.5 0.5 0.5
  0.0 0.5 0.5
  0.5 0.0 0.5
  0.5 0.5 0.0

#Gives the number of band, explicitely (do not take the default)
    nband   20

#Exchange-correlation functional

      ixc 23

#Definition of the planewave basis set

     ecut  60.0        # Maximal kinetic energy cut-off, in Hartree

#Definition of the SCF procedure (dummy)
     iscf   5          # Self-consistent calculation, using algorithm 5
    nstep   75         # Maximal number of SCF cycles
   diemac   9.0        # 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).