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[digest <trp6@case.edu>]

Dear all, 

I am trying to calculate the phonon modes of ScN using LDA.fhi and pspnc 
pseudo
potential. But the result is quite different. 

Here are the parts form my output obtained with pspnc and fhi only
respectively.  
-  2.989980E+00  2.989980E+00  2.989980E+00  2.729446E+02  2.729446E+02
-  2.729446E+02
 
 Phonon frequencies in cm-1    :
-  2.989980E+00  2.989980E+00  2.989980E+00  2.729446E+02  2.729446E+02
-  2.729446E+02

Similar order of difference persist in other q points also. 

I am surprised to see that much difference after all both being  LDA 
Troullier-Martins psp.
Any suggestion, why ?, and which to trust. I earlier did calculation with fhi
psp they give the resonable phonon in AlN, GaN. But  In this case since
experiment is not so clear, I am not sure what to trust. 

Further I obtained the similar result with LuN. 

One more question, might be related with it. Why there is use of fhi and pspnc
psp for Al and As in tutorial of AlAs in Response function. Seems like don't
made much difference but any particular reason ?

I used ixc 1 with pspnc and ixc 7 with fhi. 

And here is my input file.

# Crystalline Scn  : 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-22      # 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 4-10 : 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 2        # 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*8.49525   # is equivalent to   3*8.50
    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   21 7    # 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   2         # There are two atoms
    typat   1 2       # The first is of type 1 (Al), the second is of type 2
(As).
                                                                              
 

     xred   0.0  0.0  0.0
            0.5 0.5 0.5
                                                                              
 

#Gives the number of band, explicitely (do not take the default)
    nband   4
                                                                              
 

#Exchange-correlation functional
                                                                              
 

      ixc   1            
                                                                              
 

#Definition of the planewave basis set
                                                                              
 

     ecut   40.0           # Maximal kinetic energy cut-off, in
Hartree#Definition of the k-point grid
      ngkpt 6 6 6
  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   5          # Self-consistent calculation, using algorithm 5
    nstep   100         # Maximal number of SCF cycles

Thanks.