ndtset   3

# Set 1 : Initial self-consistent run

    iscf1   5
  kptopt1   1
  tolvrs1   1.0d-18  #need excellent convergence of GS quantities for RF runs


# Set 2 : Calculate the ddk wf's - needed for piezoelectric tensor and 
#         Born effective charges in dataset 3

  getwfk2  -1
    iscf2  -3        #this option is needed for ddk
  kptopt2   2        #use time-reversal symmetry only for k points
    nqpt2   1        #one wave vector will be specified
     qpt2   0 0 0    #need to specify gamma point
  rfelfd2   2        #set for ddk wf's only
   rfdir2   1 1 1    #full set of directions needed
  tolwfr2   1.0d-20  #only wf convergence can be monitored here

# Set 3 : response-function calculations for all needed perturbations

  getddk3  -1
  getwfk3  -2
    iscf3   5
  kptopt3   2        #use time-reversal symmetry only for k points
    nqpt3   1
     qpt3   0 0 0
  rfphon3   1        #do atomic displacement perturbation
 rfatpol3   1 12      #do for all atoms
  rfstrs3   3        #do strain perturbation
   rfdir3   1 1 1    #the full set of directions is needed
  tolvrs3   1.0d-20  #need reasonable convergence of 1st-order quantities

#Common input data


# acell  COPY RELAXED RESULT FROM PREVIOUS CALCULATION

  acell   9.9744028594E+00  1.0191379600E+01  1.2366315421E+01 

  rprim   1.00000000000  0.0000000000E+00   0.0000000000000
          0.0000000000E+00  1.0000000000E+00  0.0000000000E+00
         -6.7878247352E-01  0.0000000000E+00  7.3433939949E-01
                                 
#definition of the atom types and atoms
 ntypat   2 
  znucl   7 8
  natom   12
  typat   1 1 1 1 2 2 2 2 2 2 2 2 

#Starting approximation for atomic positions in REDUCED coordinates
# xred  COPY RELAXED RESULT FROM PREVIOUS CALCULATION

 xred         1.4920241760E-01  2.5000000000E-01  6.9968113757E-02
             -1.4920241760E-01  7.5000000000E-01 -6.9968113757E-02
              2.3243548986E-01  2.5000000000E-01  4.8723632821E-01
             -2.3243548986E-01  7.5000000000E-01 -4.8723632821E-01
              4.2504482332E-01  2.5000000000E-01  1.6046368452E-01
             -4.2504482332E-01  7.5000000000E-01 -1.6046368452E-01
              3.7655964825E-01  2.5000000000E-01  7.3942107328E-01
             -3.7655964825E-01  7.5000000000E-01 -7.3942107328E-01
              1.5936913332E-01  4.5576430188E-02  3.5213722448E-01
             -1.5936913332E-01 -4.5576430188E-02 -3.5213722448E-01
             -1.5936913332E-01  5.4557643019E-01 -3.5213722448E-01
              1.5936913332E-01  4.5442356981E-01  3.5213722448E-01

#Gives the number of bands, explicitely (do not take the default)
  nband  38              # For an insulator (if described correctly as an 
                         # insulator by DFT), conduction bands should not
                         # be included in response-function calculations

#Definition of the plane wave basis set
   ecut   25.0            # Maximum kinetic energy cutoff (Hartree)
 ecutsm   0.5            # Smoothing energy needed for lattice paramete
                         # optimization.  This will be retained for
                         # consistency throughout.

#Definition of the k-point grid
 kptopt   1              # Use symmetry and treat only inequivalent points
  ngkpt   6 6 6          
 shiftk   0.0 0.0 0.0    # This choice of origin for the k point grid
                         # preserves the hexagonal symmetry of the grid,
                         # which would be broken by the default choice.

#Definition of the self-consistency procedure
 diemac   9.0            # Model dielectric preconditioner
   iscf   5              # Use conjugate-gradient SCF cycle
  nstep   80             # Maxiumum number of SCF iterations