Dear siesta user
I am a beginner in siesta and to quantum mechanics simulation.I want to
calculate phonon frequency of (8,0) CNT.In a trial run I followed the
following steps.
a> Structural relaxation with MD.Typeofrun CG with variablecell true.
b> After I used the coordinates output of first step to calculate
MD.typeofrun FC.
my .fdf code is given below.
SystemName Phonon calculation # Descriptive name of the system
SystemLabel 8_0 # Short name for naming files
# Output options
# Species and atoms
%block ChemicalSpeciesLabel
1 6 C
%endblock ChemicalSpeciesLabel
NumberOfSpecies 1
NumberOfAtoms 32
WriteKpoints true
%block kgrid_Monkhorst_Pack
1 0 0 0.5
0 1 0 0.5
0 0 9 0.5
%endblock kgrid_Monkhorst_Pack
LatticeConstant 1 Ang
%block LatticeVectors
99.726332691 -0.002757406 0.000570988
-0.002757317 99.746420222 0.000133496
0.000023914 0.000005308 4.342493175
%endblock LatticeVectors
Messcutoff 200 Ry
xc.functional GGA # Exchange-correlation functional
xc.authors PBE
MaxSCFIterations 500 # Maximum number of SCF iter
MD.TypeOfRun FC # Type of dynamics:
#Atomic coordinates
AtomicCoordinatesFormat Fractional
AtomicCoordinatesAndAtomicSpecies < coord.fdf
After that I have used .FC file in vibrator program to generate
frequency and eigenvector.
input file for vibrator program is--
SystemName Carbon Nanotube 32 atom 8_0
SystemLabel Phonon
NumberOfatoms 32
%block ChemicalSpeciesLabel
1 6 C
%endblock ChemicalSpeciesLabel
%block BandLines
1 0.000000 0.000000 0.0000 \Gamma
5 0.000000 0.000000 1.0000 X
%endblock BandLines
LatticeConstant 1 Ang
%block LatticeVectors
99.726332691 -0.002757406 0.000570988
-0.002757317 99.746420222 0.000133496
0.000023914 0.000005308 4.342493175
%endblock LatticeVectors
Eigenvectors true
AtomicCoordinatesAndAtomicSpecies <coord.fdf
AtomicCoordinatesFormat Fractional
But I am getting negative eigenvalues and even imaginary eigenvectors .
Please help me where I am doing wrong. And suggest me which extra
parameters I should use for the same.
Thanking you.
