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[Sven Issing <sven.issing@physik.uni-wuerzburg.de>]

Dear all,

I have a question concerning the symmetry analysis of phonons in LaMnO3.
When using HGH pseudopotentials you get relatively good phonon
frequencies, but if you check the symmetry characters with anaddb
you see numbers between -1.0 and 1.0 where you would
expect only -1 and +1:

Analysis of degeneracies and characters (maximum tolerance=2.00E-05 a.u.)
Symmetry characters of vibration mode #   1
 1.0 -1.0 -0.8  0.8 -0.9  0.9  1.0 -0.9
Symmetry characters of vibration mode #   2
 1.0  0.7 -0.7 -0.8 -0.8 -0.6  0.8  0.7
Symmetry characters of vibration mode #   3
 1.0 -0.6  0.5 -0.8 -0.6  0.3 -0.1  0.4
Symmetry characters of vibration mode #   4
       degenerate with vibration mode #   5
 2.0 -0.1 -1.5 -0.3 -1.9  0.2  1.6  0.3
Symmetry characters of vibration mode #   6
 1.0  0.2  0.5  0.1  0.2  0.1  0.6  0.2

and so on.

I did the same calculation with TM pseudopotentials again.
There the symmetry characters are just -1 or +1 just
as you would expect - shown here:

Analysis of degeneracies and characters (maximum tolerance=1.00E-06 a.u.)
Symmetry characters of vibration mode #   1
      degenerate with vibration modes #   2 to    3
 3.0 -1.0 -1.0 -1.0 -3.0  1.0  1.0  1.0
Symmetry characters of vibration mode #   4
 1.0  1.0  1.0  1.0  1.0  1.0  1.0  1.0
Symmetry characters of vibration mode #   5
 1.0  1.0 -1.0 -1.0 -1.0 -1.0  1.0  1.0
Symmetry characters of vibration mode #   6
 1.0 -1.0 -1.0  1.0 -1.0  1.0  1.0 -1.0
Symmetry characters of vibration mode #   7
 1.0 -1.0  1.0 -1.0  1.0 -1.0  1.0 -1.0
Symmetry characters of vibration mode #   8
 1.0 -1.0 -1.0  1.0  1.0 -1.0 -1.0  1.0

and so on.

Is this an effect intrinsic to the used pseudopotentials
or is my first calculation simply not very good converged?
Or something completely different...

For clarity I attached my input files for the
response function calculation and the anaddb
input-file.

Thank you for any suggestions!

Sven


--
Sven Issing
Experimentelle Physik III
Physikalisches Institut der Universität Würzburg
Am Hubland
97074 Würzburg

Tel.: +49 (0)931 8885777
Fax:  +49 (0)931 8885142
Email: sven.issing@physik.uni-wuerzburg.de

!Input file for the anaddb code. Analysis of the LaMnO3 DDB

!Wavevector grid number 1 (coarse grid, from DDB)
  ngqpt   4  4  4   ! Monkhorst-Pack indices
  nqshft  1         ! number of q-points in repeated basic q-cell
  q1shft  3*0.5

!Wavevector = gamma point
  nph1l 1

  qph1l 0.000 0.000 0.000 1.0

!Output of phonon eigenvectors and eigendisplacements
  eivec 1

# This line added when defaults were changed (v5.3) to keep the previous, old 
behaviour
  symdynmat 0
# Crystalline LaMnO3 : computation of the response to homogeneous
# electric field and atomic displacements, at q=0

ndtset  3

#Ground state calculation
  kptopt1   1             # Automatic generation of k points, taking
                          # into account the symmetry
  tolvrs1   1.0d-8        # SCF stopping criterion
    iscf1   7             # Self-consistent calculation, using algorithm 7
   nstep1   100

#Response Function calculation : d/dk
  rfelfd2   2             # Activate the calculation of the d/dk perturbation
   rfdir2   1 1 1         # Need to consider the perturbation in all 
directions (orthorombic crystal)
    nqpt2   1
     qpt2   0.0 0.0 0.0   # This is a calculation at the Gamma point

  getwfk2   -1            # Uses as input the output wf of the previous 
dataset

  kptopt2   2             # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.

    iscf2  -3             # The d/dk perturbation must be treated 
                          # in a non-self-consistent way
  tolwfr2   1.0d-3        # Must use tolwfr for non-self-consistent 
calculations
                          # Here, the value of tolwfr is very low.
   nstep2   100

#Response Function calculation : phonons
  rfphon3   1             # Activate the calculation of the atomic 
dispacement perturbations
 rfatpol3   1 20          # All the atoms will be displaced
   rfdir3   1 1 1         # Need to calculate perturbations in all directions 
(orthorombic lattice)
    nqpt3   1
     qpt3   0.0 0.0 0.0   # This is a calculation at the Gamma point

  getwfk3   -2            # Uses as input wfs the output wfs of the dataset 1
  getddk3   -1            # Uses as input ddk wfs the output of the dataset 2

  kptopt3   2             # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs3   1.0d-2
    iscf3   7             # Self-consistent calculation, using algorithm 7
   nstep3   75

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


ecut 70

acell 1.0043195597E+01  1.4194782360E+01  1.0087746005E+01 Bohr

rprim 1 0 0
      0 1 0
      0 0 1

spgroup 62
spgaxor 1
spgorig 1
brvltt 1
natrd 4

ntypat 3
znucl 57 25 8

natom 20
typat 1 2 3 3
xred
      0.5246   0.25    0.0093
      0        0       0
     -0.0057   0.25   -0.0621
      0.2787   0.0349  0.2292

nband 70

ixc 1             # LDA HGH parametrization

kptopt   1             # Automatic generation of k points, taking

nshiftk 1
shiftk  0.5 0.5 0.5

ngkpt  4 4 4

diemac 20

nline   12
nnsclo  3

# Crystalline LaMnO3 : computation of the response to homogeneous
# electric field and atomic displacements, at q=0

ndtset  3

#Ground state calculation
  kptopt1   1             # Automatic generation of k points, taking
                          # into account the symmetry
  tolvrs1   5.0d-6        # SCF stopping criterion
    iscf1   7             # Self-consistent calculation, using algorithm 7
   nstep1   100

#Response Function calculation : d/dk
  rfelfd2   2             # Activate the calculation of the d/dk perturbation
   rfdir2   1 1 1         # Need to consider the perturbation in all 
directions (orthorombic crystal)
    nqpt2   1
     qpt2   0.0 0.0 0.0   # This is a calculation at the Gamma point

  getwfk2   -1            # Uses as input the output wf of the previous 
dataset

  kptopt2   2             # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.

    iscf2  -3             # The d/dk perturbation must be treated 
                          # in a non-self-consistent way
  tolwfr2   3.5d-3        # Must use tolwfr for non-self-consistent 
calculations
                          # Here, the value of tolwfr is very low.
   nstep2   50

#Response Function calculation : electric field perturbation and phonons
  rfphon3   1             # Activate the calculation of the atomic 
dispacement perturbations
 rfatpol3   1 20          # All the atoms will be displaced
  rfelfd3   3             # Activate the calculation of the electric field 
perturbation
   rfdir3   1 1 1         # Need to consider the perturbation in all 
directions (orthorombic crystal)

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

  getwfk3   -2            # Uses as input wfs the output wfs of the dataset 1
  getddk3   -1            # Uses as input ddk wfs the output of the dataset 2

  kptopt3   2             # Automatic generation of k points,
                          # using only the time-reversal symmetry to decrease
                          # the size of the k point set.
  tolvrs3   1.0d3
    iscf3   7             # Self-consistent calculation, using algorithm 7
   nstep3   75

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


ecut 70

acell 10.024781561 14.168756457 10.069797033

rprim 1 0 0
      0 1 0
      0 0 1

spgroup 62
spgaxor 1
spgorig 1
brvltt 1
natrd 4

ntypat 3
znucl 57 25 8

natom 20
typat 1 2 3 3
xred
      0.5246   0.25    0.0093
      0        0       0
     -0.0057   0.25   -0.0621
      0.2787   0.0349  0.2292

nband 90

ixc 1             # LDA HGH parametrization

kptopt   1             # Automatic generation of k points, taking

nshiftk 1
shiftk  0.5 0.5 0.5

ngkpt  4 4 4

diemac 20

nline   12
nnsclo  3