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[Shaorui Sun <sunsr@ihep.ac.cn>]

Dear all:
     When I calculate the phonon mode of Ge,my result is different from the 
experimental result which is shown in the follow table.
                experimental(cm-1)    computational(cm-1)
Gamma(TO)         304                    289
Gamma(LO)         304                    289
X(TA)              80                     78
X(LA)             241                    226
X(TO)             276                    251
X(LO)             241                    226
L(TA)              63                     62
L(LA)             222                    215
L(TO)             290                    271
L(LO)             245                    220
--------------------------------------------------------
It also looks like that the difference is more obvious with higher 
frequency.My inout is shown as follows:
-----------------------------------------------------------------------
ndtset 6

#Definition of the k-point grids
kptopt 1          # Option for the automatic generation of k points, taking
                  # into account the symmetry
nshiftk 4
shiftk  0.5 0.5 0.5  # These shifts will be the same for all grids
        0.5 0.0 0.0
        0.0 0.5 0.0
        0.0 0.0 0.5

ngkpt  8 8 8     # Definition of the different grids

#Ground state calculation                               
  kptopt1   1             # Automatic generation of k po
                          # into account the symmetry   
  tolvrs1   1.0d-18       # SCF stopping criterion      
    iscf1   5             # Self-consistent calculation,
  prtden1   1             # Will be needed for dataset 4

#Response Function calculation : phonon at X                              
  rfphon2   1             # Activate the calculation of the atomic dispace
 rfatpol2   1 1           # All the atoms will be displaced               
   rfdir2   1 1 1         # Need to consider the perturbation in the x-dir
                                                                          
    nqpt2   1                                                             
     qpt2   0.0 0.5 0.5   # This is a calculation at the X point          
                                                                          
  getwfk2   1             # Uses as input wfs the output wfs of the datase
                                                                          
  kptopt2   3             # Automatic generation of k points,             
                          # no use of symmetries to decrease              
                          # the size of the k point set.                  
  tolvrs2   1.0d-8                                                        
    iscf2   5             # Self-consistent calculation, using algorithm 5
 
#Response Function calculation : phonon at L                              
  rfphon3   1             # Activate the calculation of the atomic dispace
 rfatpol3   1 1           # All the atoms will be displaced               
   rfdir3   1 1 1         # Need to consider the perturbation in the x-dir
                                                                          
    nqpt3   1                                                             
     qpt3   0.5 0.0 0.0   # This is a calculation at the L point          
                                                                          
  getwfk3   1             # Uses as input wfs the output wfs of the datase
                                                                          
  kptopt3   3             # Automatic generation of k points,             
                          # no use of symmetries to decrease              
                          # the size of the k point set.                  
  tolvrs3   1.0d-8                                                        
    iscf3   5             # Self-consistent calculation, using algorithm 5

#Response Function calculation : phonon at Gamma
  rfphon4   1             # Activate the calculation of the atomic 
dispacement p
erturbations
 rfatpol4   1 1           # All the atoms will be displaced
   rfdir4   1 1 1         # Need to consider the perturbation in the 
x-direction
 only

    nqpt4   1
     qpt4   0.0 0.0 0.0   # This is a calculation at the Gamma point

  getwfk4   1            # Uses as input wfs the output wfs of the dataset 1

  kptopt4   2            # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs4   1.0d-8
    iscf4   5             # Self-consistent calculation, using algorithm 

#Response Function calculation : phonon at K
  rfphon5   1             # Activate the calculation of the atomic 
dispacement p
erturbations
 rfatpol5   1 1           # All the atoms will be displaced
   rfdir5   1 1 1         # Need to consider the perturbation in the 
x-direction
 only

    nqpt5   1
     qpt5   3/8 3/8 1/2   # This is a calculation at the Gamma point
       
  getwfk5   1            # Uses as input wfs the output wfs of the dataset 1

  kptopt5   3            # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs5   1.0d-8
    iscf5   5             # Self-consistent calculation, using algorithm

#Response Function calculation : phonon at W
  rfphon6   1             # Activate the calculation of the atomic 
dispacement p
erturbations
 rfatpol6   1 1           # All the atoms will be displaced
   rfdir6   1 1 1         # Need to consider the perturbation in the 
x-direction
 only

    nqpt6   1
     qpt6   0.25 0.25 0.75   # This is a calculation at the Gamma point

  getwfk6   1            # Uses as input wfs the output wfs of the dataset 1

  kptopt6   3            # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs6   1.0d-8
    iscf6   5             # Self-consistent calculation, using algorithm




#Definition of the unit cell
acell 3*10.68          # This is equivalent to   10.18 10.18 10.18
rprim  0.0  0.5  0.5   # FCC primitive vectors (to be scaled by acell)
       0.5  0.0  0.5   
       0.5  0.5  0.0

#Definition of the atom types
ntypat 1          # There is only one type of atom
znucl 32          # 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, the only type is Silicon.
                         

#Definition of the atoms
natom 2           # There are two atoms
typat 1 1         # They both are of type 1, that is, Silicon.
xred              # This keyword indicate that the location of the atoms
                  # 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.

#Definition of the planewave basis set
ecut  8.0         # Maximal kinetic energy cut-off, in Hartree

#Definition of the SCF procedure
nstep 20          # Maximal number of SCF cycles

diemac 13.0       # 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.
                  # Here, we follow the prescription for bulk silicon.
[wien2k@bsrf-serv temp]$ vi Ge.in
#Crystalline silicon : computation of the total energy
# Convergence with respect to the number of k points.

ndtset 6

#Definition of the k-point grids
kptopt 1          # Option for the automatic generation of k points, taking
                  # into account the symmetry
nshiftk 4
shiftk  0.5 0.5 0.5  # These shifts will be the same for all grids
        0.5 0.0 0.0
        0.0 0.5 0.0
        0.0 0.0 0.5

ngkpt  8 8 8     # Definition of the different grids

#Ground state calculation
  kptopt1   1             # Automatic generation of k po
                          # into account the symmetry
  tolvrs1   1.0d-18       # SCF stopping criterion
    iscf1   5             # Self-consistent calculation,
  prtden1   1             # Will be needed for dataset 4

#Response Function calculation : phonon at X
  rfphon2   1             # Activate the calculation of the atomic dispace
 rfatpol2   1 1           # All the atoms will be displaced
   rfdir2   1 1 1         # Need to consider the perturbation in the x-dir

    nqpt2   1
     qpt2   0.0 0.5 0.5   # This is a calculation at the X point

  getwfk2   1             # Uses as input wfs the output wfs of the datase

  kptopt2   3             # Automatic generation of k points,
                          # no use of symmetries to decrease
                          # the size of the k point set.
  tolvrs2   1.0d-8
    iscf2   5             # Self-consistent calculation, using algorithm 5

#Response Function calculation : phonon at L
  rfphon3   1             # Activate the calculation of the atomic dispace
 rfatpol3   1 1           # All the atoms will be displaced
   rfdir3   1 1 1         # Need to consider the perturbation in the x-dir

    nqpt3   1
     qpt3   0.5 0.0 0.0   # This is a calculation at the L point

  getwfk3   1             # Uses as input wfs the output wfs of the datase

  kptopt3   3             # Automatic generation of k points,
                          # no use of symmetries to decrease
                          # the size of the k point set.
  tolvrs3   1.0d-8
    iscf3   5             # Self-consistent calculation, using algorithm 5

#Response Function calculation : phonon at Gamma
  rfphon4   1             # Activate the calculation of the atomic 
dispacement p
erturbations
 rfatpol4   1 1           # All the atoms will be displaced
   rfdir4   1 1 1         # Need to consider the perturbation in the 
x-direction
 only

    nqpt4   1
     qpt4   0.0 0.0 0.0   # This is a calculation at the Gamma point

  getwfk4   1            # Uses as input wfs the output wfs of the dataset 1

  kptopt4   2            # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs4   1.0d-8
    iscf4   5             # Self-consistent calculation, using algorithm

#Response Function calculation : phonon at K
  rfphon5   1             # Activate the calculation of the atomic 
dispacement p
erturbations
 rfatpol5   1 1           # All the atoms will be displaced
   rfdir5   1 1 1         # Need to consider the perturbation in the 
x-direction
 only

    nqpt5   1
     qpt5   3/8 3/8 1/2   # This is a calculation at the Gamma point

  getwfk5   1            # Uses as input wfs the output wfs of the dataset 1

  kptopt5   3            # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs5   1.0d-8
    iscf5   5             # Self-consistent calculation, using algorithm

#Response Function calculation : phonon at W
  rfphon6   1             # Activate the calculation of the atomic 
dispacement p
erturbations
 rfatpol6   1 1           # All the atoms will be displaced
   rfdir6   1 1 1         # Need to consider the perturbation in the 
x-direction
 only

    nqpt6   1
     qpt6   0.25 0.25 0.75   # This is a calculation at the Gamma point

  getwfk6   1            # Uses as input wfs the output wfs of the dataset 1

  kptopt6   3            # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs6   1.0d-8
    iscf6   5             # Self-consistent calculation, using algorithm




#Definition of the unit cell
acell 3*10.68          
rprim  0.0  0.5  0.5   # FCC primitive vectors (to be scaled by acell)
       0.5  0.0  0.5
       0.5  0.5  0.0

#Definition of the atom types
ntypat 1          # There is only one type of atom
znucl 32          # 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, the only type is Silicon.


#Definition of the atoms
natom 2           # There are two atoms
typat 1 1         # They both are of type 1, that is, Silicon.
xred              # This keyword indicate that the location of the atoms
                  # 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.

#Definition of the planewave basis set
ecut  8.0         # Maximal kinetic energy cut-off, in Hartree

#Definition of the SCF procedure
nstep 20          # Maximal number of SCF cycles

diemac 13.0       # 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.
                  # Here, we follow the prescription for bulk silicon.
----------------------------------------------------------------------
Who could give me some suggestion or direction?
Thanks in advance!


Best Regards!
                        S. R. Sun
---------------------------------------------
Beijing Synchrotron Radiation Facility
Institute of High Energy Physics
Chinese Academy of Sciences
P. O. Box 918, 100049 Beijing
P. R. China
Tel: 0086+10 88236710
email:sunsr@ihep.ac.cn