Positive frequency at Gamma for cubic BaTiO3
Posted: Tue Jun 17, 2014 2:36 am
I'm trying to compute the phonon frequencies at Gamma for materials such as cubic BaTiO3, which is reported in literature to have a negative frequency of about 200cm-1 at Gamma. However, the calculation results are different from that of the literature (Lattice dynamics of BaTiO3, PbTiO3 and PbZrO3: a comparative first-principles study). The obtained frequencies at Gamma is all positive. Please tell me how to manage this problem.
Here is a part of my input and output files:
Here is a part of my input and output files:
Code: Select all
ndtset 3
#Ground state calculation
kptopt1 1 # Automatic generation of k points, taking
# into account the symmetry
tolvrs1 1.0d-18 # SCF stopping criterion
iscf1 5 # Self-consistent calculation, using algorithm 5
#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 the x-direction only
# This is rather specific, due to the high symmetry of the AlAs crystal
# In general, just use rfdir 1 1 1
# In the present version of ABINIT (v4.6), symmetry cannot be used
# to reduce the number of ddk perturbations
npfft 1
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-18 # Must use tolwfr for non-self-consistent calculations
# Here, the value of tolwfr is very low.
#Response Function calculation : electric field perturbation and phonons
rfphon3 1 # Activate the calculation of the atomic dispacement perturbations
rfatpol3 1 5 # All the atoms will be displaced
rfelfd3 3 # Activate the calculation of the electric field perturbation
rfdir3 1 1 1 # All directions are selected. However, symmetries will be used to decrease
# the number of perturbations, so only the x electric field is needed
# (and this explains why in the second dataset, rfdir was set to 1 0 0).
nqpt3 1
qpt3 0.0 0.0 0.0 # This is a calculation at the Gamma point
getwfk3 1 # Uses as input wfs the output wfs of the dataset 1
getddk3 2 # 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-18
iscf3 5 # Self-consistent calculation, using algorithm 5
#######################################################################
acell 3*1.0
rprim
7.90086702951612E+00 0.000000000000000 0.000000000000000
0.000000000000000 7.90086702951612E+00 0.000000000000000
0.000000000000000 0.000000000000000 7.90086702951612E+00
ntypat 3
znucl 8 56 22
natom 5
typat 3*1 2 3
xred
0.500000000000000 0.500000000000000 0
0.500000000000000 0.0000000000000000 0.5
0.0000000000000000 0.500000000000000 0.5
0.0000000000000000 0.0000000000000000 0
0.500000000000000 0.500000000000000 0.5000000000000000
#Gives the number of band, explicitely (do not take the default)
nband 18 # For an insulator (if described correctly as an insulator
# by DFT), there is no need to include conduction bands
# in response-function calculations
#Exchange-correlation functional
ixc 1 # LDA Teter Pade parametrization
#Definition of the planewave basis set
ecut 40.0 # Maximal kinetic energy cut-off, in Hartree
nshiftk 1
shiftk 0.0 0.0 0.0
ngfft 48 48 48
ngkpt 4 4 4
occopt 7 # Fermi-Dirac
tsmear 0.02 # ~0.2 eV, Default 0.04Ha
#Definition of the SCF procedure
nstep 100 # Maximal number of SCF cycles
diemac 9.0 # 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.
# The dielectric constant of AlAs is smaller that the one of Si (=12).
# add to conserve old < 6.7.2 behavior for calculating forces at each SCF step
optforces 1
Code: Select all
trf1_1.in
trf1_1.out
trf1_1i
trf1_1o
trf1_1
8o.pspnc
56ba.pspnc
22ti.pspnc
Code: Select all
trf1_1.out
Phonon wavevector (reduced coordinates) : 0.00000 0.00000 0.00000
Phonon energies in Hartree :
2.995340E-04 2.995340E-04 2.996006E-04 9.021911E-04 9.021911E-04
9.022290E-04 1.232878E-03 1.232878E-03 1.232878E-03 1.272832E-03
1.272834E-03 1.272834E-03 2.249139E-03 2.249162E-03 2.249162E-03
Phonon frequencies in cm-1 :
- 6.574012E+01 6.574012E+01 6.575473E+01 1.980080E+02 1.980080E+02
- 1.980164E+02 2.705854E+02 2.705854E+02 2.705854E+02 2.793543E+02
- 2.793548E+02 2.793548E+02 4.936290E+02 4.936340E+02 4.936340E+02
Phonon at Gamma, with non-analyticity in the
direction (cartesian coordinates) 1.00000 0.00000 0.00000
Phonon energies in Hartree :
2.995340E-04 2.996006E-04 3.329321E-04 9.021911E-04 9.022290E-04
1.096572E-03 1.232878E-03 1.232878E-03 1.232878E-03 1.272832E-03
1.272834E-03 1.939203E-03 2.249139E-03 2.249162E-03 3.124761E-03
Phonon frequencies in cm-1 :
- 6.574012E+01 6.575473E+01 7.307015E+01 1.980080E+02 1.980164E+02
- 2.406698E+02 2.705854E+02 2.705854E+02 2.705854E+02 2.793543E+02
- 2.793548E+02 4.256059E+02 4.936290E+02 4.936340E+02 6.858057E+02
Phonon at Gamma, with non-analyticity in the
direction (cartesian coordinates) 0.00000 1.00000 0.00000
Phonon energies in Hartree :
2.995340E-04 2.996006E-04 3.329321E-04 9.021911E-04 9.022290E-04
1.096572E-03 1.232878E-03 1.232878E-03 1.232878E-03 1.272832E-03
1.272834E-03 1.939203E-03 2.249139E-03 2.249162E-03 3.124761E-03
Phonon frequencies in cm-1 :
- 6.574012E+01 6.575473E+01 7.307015E+01 1.980080E+02 1.980164E+02
- 2.406698E+02 2.705854E+02 2.705854E+02 2.705854E+02 2.793543E+02
- 2.793548E+02 4.256059E+02 4.936290E+02 4.936340E+02 6.858057E+02
Phonon at Gamma, with non-analyticity in the
direction (cartesian coordinates) 0.00000 0.00000 1.00000
Phonon energies in Hartree :
2.995340E-04 2.995340E-04 3.329789E-04 9.021911E-04 9.021911E-04
1.096644E-03 1.232878E-03 1.232878E-03 1.232878E-03 1.272834E-03
1.272834E-03 1.939211E-03 2.249162E-03 2.249162E-03 3.124751E-03
Phonon frequencies in cm-1 :
- 6.574012E+01 6.574012E+01 7.308042E+01 1.980080E+02 1.980080E+02
- 2.406854E+02 2.705854E+02 2.705854E+02 2.705854E+02 2.793548E+02
- 2.793548E+02 4.256077E+02 4.936340E+02 4.936340E+02 6.858035E+02
== END DATASET(S) ==============================================================
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