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Dear abinit developers and users,

How can I calculate the vibrational modes of a molecule in the response function calculation?

I calculated the vibrational modes of a water molecule, however the result was not so good compared to the experimental values, which are 3657, 1595, and 3756 cm^-1.
I obtained the following data on the phonon frequencies:

Phonon frequencies in cm-1 :
- -2.900103E+01 -2.152243E+01 2.406617E+01 2.513014E+01 2.999595E+01
- 3.216054E+01 1.545422E+03 3.014001E+03 3.061785E+03

It seems that last three data, 1.545433E+03, 3.014097E+03, and 3.061884E+03, corresponds to the vibrational modes. I think that the remaining data should be zero, however it has a finite value.

The following is my input file. I used the norm conserving potential of the TM type and used the optimized structure of a water molecule with ionmov=3.

# H2O molecule : computation of the response to atomic displacements, at q=0

ndtset 2

#Ground state calculation
kptopt1 1

tolvrs1 1.0d-18
iscf1 7

#Response Function calculation : phonons
rfphon2 1
rfatpol2 1 3
rfdir2 1 1 1

nqpt2 1
qpt2 0.0 0.0 0.0

getwfk2 1
kptopt2 2

tolvrs2 1.0d-8
iscf2 7

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

#Definition of the unit cell
acell 3*20.d0

#Definition of the atom types
ntypat 2
znucl 8 1

#Definition of the atoms
natom 3
typat 1*1 2*2
xangst # Optimized at acell=3*20.d0, ecut=30
-8.7627647649E-03 0.0000000000E+00 -6.8189885013E-03
-1.2439566631E-02 0.0000000000E+00 9.8344879088E-01
9.4928433140E-01 0.0000000000E+00 -2.5738380238E-01

#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 30

#Definition of the k-point grid
ngkpt 1 1 1
nshiftk 1
shiftk 0.0 0.0 0.0

#Definition of the SCF procedure
nstep 100
diemac 2.0d0