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Dear Abinit Users we are trying to get Phonon dispersion for NiAs type structure having space group 194.
we are getting the frequency at gamma points as below.


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Phonon wavevector (reduced coordinates) : 0.00000 0.00000 0.00000
Phonon energies in Hartree :
-9.145779E-04 -1.524835E-05 -1.502503E-05 1.588411E-05 2.956834E-04
2.956834E-04 9.120017E-04 1.707131E-03 1.707183E-03 1.931110E-03
1.931151E-03 2.327343E-03
Phonon frequencies in cm-1 :
- -2.007266E+02 -3.346626E+00 -3.297612E+00 3.486160E+00 6.489500E+01
- 6.489500E+01 2.001612E+02 3.746719E+02 3.746833E+02 4.238296E+02
- 4.238386E+02 5.107928E+02

Phonon at Gamma, with non-analyticity in the
direction (cartesian coordinates) 1.00000 0.00000 0.00000
Phonon energies in Hartree :
-9.145779E-04 -1.523278E-05 1.588355E-05 4.021682E-05 2.956834E-04
2.956834E-04 9.120017E-04 1.707131E-03 1.794461E-03 1.931110E-03
1.931151E-03 2.327343E-03
Phonon frequencies in cm-1 :
- -2.007266E+02 -3.343209E+00 3.486036E+00 8.826573E+00 6.489500E+01
- 6.489500E+01 2.001612E+02 3.746720E+02 3.938387E+02 4.238296E+02
- 4.238386E+02 5.107928E+02

Phonon at Gamma, with non-analyticity in the
direction (cartesian coordinates) 0.00000 1.00000 0.00000
Phonon energies in Hartree :
-9.145779E-04 -1.504092E-05 1.588393E-05 4.015162E-05 2.956834E-04
2.956834E-04 9.120017E-04 1.707183E-03 1.794412E-03 1.931110E-03
1.931151E-03 2.327343E-03
Phonon frequencies in cm-1 :
- -2.007266E+02 -3.301100E+00 3.486119E+00 8.812262E+00 6.489500E+01
- 6.489500E+01 2.001612E+02 3.746833E+02 3.938279E+02 4.238296E+02
- 4.238386E+02 5.107928E+02

Phonon at Gamma, with non-analyticity in the
direction (cartesian coordinates) 0.00000 0.00000 1.00000
Phonon energies in Hartree :
-8.752769E-04 -1.524809E-05 -1.502477E-05 6.247984E-05 2.956834E-04
2.956834E-04 9.120017E-04 1.707131E-03 1.707183E-03 1.931110E-03
1.931151E-03 2.327343E-03
Phonon frequencies in cm-1 :
- -1.921011E+02 -3.346569E+00 -3.297556E+00 1.371274E+01 6.489500E+01
- 6.489500E+01 2.001612E+02 3.746719E+02 3.746833E+02 4.238296E+02
- 4.238386E+02 5.107928E+02

================================================================================
== DATASET 4 ==================================================================
##################################################################################
The Problem is that
The first three frequencies should be equal but here the first frequency of the acoustic part among three is largely differ in values.
Need yours valuable suggestions.
Hoping with Positive reply

SANJAY D GUPTA
Junior Research Fellow
and PhD candidate
Department of Physics
Bhavanagar University
Bhavnagar -364022

*******************************************8

the input file for Phonon calculation is as below..
#######################################################
# Crystalline Palladium Carbide : computation of the phonon spectrum
ndtset 52
#Set 1 : ground state self-consistency

getwfk1 0 # Cancel default
kptopt1 1 # Automatic generation of k points, taking

nqpt1 0 # Cancel default
tolvrs1 1.0d-22 # 1.0d-18 # SCF stopping criterion (modify default)
rfphon1 0 # Cancel default
prtwf1 1
prtden1 1


nqpt 1
qpt2 0.00000000E+00 0.00000000E+00 0.00000000E+00
qpt3 0.00000000E+00 0.00000000E+00 0.00000000E+00
qpt4 1.25000000E-01 0.00000000E+00 0.00000000E+00
qpt5 2.50000000E-01 0.00000000E+00 0.00000000E+00
qpt6 3.75000000E-01 0.00000000E+00 0.00000000E+00
qpt7 5.00000000E-01 0.00000000E+00 0.00000000E+00
qpt8 1.25000000E-01 1.25000000E-01 0.00000000E+00
qpt9 2.50000000E-01 1.25000000E-01 0.00000000E+00
qpt10 3.75000000E-01 1.25000000E-01 0.00000000E+00
qpt11 2.50000000E-01 2.50000000E-01 0.00000000E+00
qpt12 3.75000000E-01 2.50000000E-01 0.00000000E+00
qpt13 0.00000000E+00 0.00000000E+00 1.25000000E-01
qpt14 1.25000000E-01 0.00000000E+00 1.25000000E-01
qpt15 2.50000000E-01 0.00000000E+00 1.25000000E-01
qpt16 3.75000000E-01 0.00000000E+00 1.25000000E-01
qpt17 5.00000000E-01 0.00000000E+00 1.25000000E-01
qpt18 1.25000000E-01 1.25000000E-01 1.25000000E-01
qpt19 2.50000000E-01 1.25000000E-01 1.25000000E-01
qpt20 3.75000000E-01 1.25000000E-01 1.25000000E-01
qpt21 2.50000000E-01 2.50000000E-01 1.25000000E-01
qpt22 3.75000000E-01 2.50000000E-01 1.25000000E-01
qpt23 0.00000000E+00 0.00000000E+00 2.50000000E-01
qpt24 1.25000000E-01 0.00000000E+00 2.50000000E-01
qpt25 2.50000000E-01 0.00000000E+00 2.50000000E-01
qpt26 3.75000000E-01 0.00000000E+00 2.50000000E-01
qpt27 5.00000000E-01 0.00000000E+00 2.50000000E-01
qpt28 1.25000000E-01 1.25000000E-01 2.50000000E-01
qpt29 2.50000000E-01 1.25000000E-01 2.50000000E-01
qpt30 3.75000000E-01 1.25000000E-01 2.50000000E-01
qpt31 2.50000000E-01 2.50000000E-01 2.50000000E-01
qpt32 3.75000000E-01 2.50000000E-01 2.50000000E-01
qpt33 0.00000000E+00 0.00000000E+00 3.75000000E-01
qpt34 1.25000000E-01 0.00000000E+00 3.75000000E-01
qpt35 2.50000000E-01 0.00000000E+00 3.75000000E-01
qpt36 3.75000000E-01 0.00000000E+00 3.75000000E-01
qpt37 5.00000000E-01 0.00000000E+00 3.75000000E-01
qpt38 1.25000000E-01 1.25000000E-01 3.75000000E-01
qpt39 2.50000000E-01 1.25000000E-01 3.75000000E-01
qpt40 3.75000000E-01 1.25000000E-01 3.75000000E-01
qpt41 2.50000000E-01 2.50000000E-01 3.75000000E-01
qpt42 3.75000000E-01 2.50000000E-01 3.75000000E-01
qpt43 0.00000000E+00 0.00000000E+00 5.00000000E-01
qpt44 1.25000000E-01 0.00000000E+00 5.00000000E-01
qpt45 2.50000000E-01 0.00000000E+00 5.00000000E-01
qpt46 3.75000000E-01 0.00000000E+00 5.00000000E-01
qpt47 5.00000000E-01 0.00000000E+00 5.00000000E-01
qpt48 1.25000000E-01 1.25000000E-01 5.00000000E-01
qpt49 2.50000000E-01 1.25000000E-01 5.00000000E-01
qpt50 3.75000000E-01 1.25000000E-01 5.00000000E-01
qpt51 2.50000000E-01 2.50000000E-01 5.00000000E-01
qpt52 3.75000000E-01 2.50000000E-01 5.00000000E-01

#Set 2 : Response function calculation of d/dk wave function

iscf2 -3
kptopt2 2
rfphon2 0 # Cancel default
rfelfd2 2 # Calculate d/dk wave function only
# tolvrs2 0.0 # Cancel default for d/dk
tolwfr2 1.0d-20 # 1.0d-16 # Use wave function residual criterion instead
prtwf2 2
prtden2 2
#Set 3 : Response function calculation of Q=0 phonons and electric field pert.
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 4 # Treat displacements of all atoms
rfdir 1 1 1 # Do all directions (symmetry will be used)
tolvrs 1.0d-10 #6 # This default is active for sets 3-10

##Common input variables
#Definition of the unit cell
acell 5.7149227270E+00 5.7149227270E+00 1.0279242564E+01
spgroup 194
angdeg 90 90 120
brvltt -1
#Definition of the atom types
ntypat 2
znucl 46 6

#Definition of the atoms
natom 4
typat 1 1 2 2 #

xred 0.0 0.0 0.0
0.0 0.0 0.5
0.33333333 0.66666666 0.25
0.66666666 0.33333333 0.75

#Definition of bands and occupation
nband 32
occopt 3
tsmear 0.01

#Exchange-correlation functional
ixc 1

#Definition of the planewave basis set
ecut 40 # Maximal kinetic energy cut-off, in Hartree
ecutsm 0.5
dilatmx 1.2

#Definition of the k-point grid
diemac 50.0
iscf 7
ngkpt 3*8
nshiftk 1
shiftk 0.0 0.0 0.5
nstep 100

##############################################
typat 1 1 2 2 #

xred 0.0 0.0 0.0
0.0 0.0 0.5
0.33333333 0.66666666 0.25
0.66666666 0.33333333 0.75

#Definition of bands and occupation
nband 32
occopt 3
tsmear 0.01

#Exchange-correlation functional
ixc 1

#Definition of the planewave basis set
ecut 40 # Maximal kinetic energy cut-off, in Hartree
ecutsm 0.5
dilatmx 1.2

#Definition of the k-point grid
diemac 50.0
iscf 7
ngkpt 3*8
nshiftk 1
shiftk 0.0 0.0 0.5
nstep 100

##############################################

Dear Sanjay,

not only are they different, but one of them is very large for an acoustic phonon mode.It could be a convergence problem. Have you checked the convergence of the phonon frequencies wrt ecut?

Igor Lukacevic