Hi everybody,
I am trying to relax & then calculate the phonon frequencies of
different carbon systems using siesta & fcbuild & vibra.
For diamond structure- at Gamma point:
my results-> phonon freq= 0.3, 2042 cm-1. (only Gamma point calculation)
& phonon freq= 0.50, 2163 cm-1 (Gamma to L-direction, 20
points),
while expt result -> 1333 cm-1.
For graphite structure, at Gamma point,
my results-> phonon freq.= 0.0, 1121.27 & 2305.7 cm-1, (only Gamma point
calculation)
while expt result- > 0.0, 900 & 1600 cm-1.
Can anybody please suggest me, why are these discrepancies in
phonon frequencies? What should I do now to get rid of this
huge error?
Here is my sample relaxation input file(that creats .FC file,
used to get phonon freq. through vibrator) for graphite -- >
best regards, mousumi
***********************************************************************
SystemName Carbon in graphite # Descriptive name of the system
SystemLabel graphite # Short name for naming files
NumberOfAtoms 4 # Number of atoms
NumberOfSpecies 1 # Number of species
%block Chemical_Species_Label
1 6 C
%endblock Chemical_Species_Label
PAO.BasisSize SZ
# Lattice, coordinates, k-sampling
%block kgrid_Monkhorst_Pack
7 0 0 0.0
0 7 0 0.0
0 0 5 0.0
%endblock kgrid_Monkhorst_Pack
AtomicCoordinatesFormat Fractional # Format for coordinates
AtomicCoorFormatOut Ang
%block AtomicCoordinatesAndAtomicSpecies
0.33333334326744 0.33333334326744 0.00000000000000 1
0.66666668653488 0.66666668653488 0.00000000000000 1
0.00000000000000 0.00000000000000 0.50000000000000 1
0.33333334326744 0.33333334326744 0.50000000000000 1
%endblock AtomicCoordinatesAndAtomicSpecies
%block LatticeVectors
1.0000000000000000 0.00000000000000000000 0.000000000000000000
0.5000000000000000 0.86602540378443864676 0.000000000000000000
0.0000000000 0.0000000000 2.1200000000000000000
%endblock LatticeVectors
LatticeConstant 2.5100000 Ang
#kgrid_cutoff 7. Ang
XC.functional LDA # Exchange-correlation functional type
XC.authors CA # Particular parametrization of xc func
SpinPolarized .false. # Spin unpolarized calculation
MeshCutoff 200. Ry # Equivalent planewave cutoff for the
grid
MaxSCFIterations 100 # Maximum number of SCF iterations per
step
DM.MixingWeight 0.3 # New DM amount for next SCF cycle
DM.Tolerance 1.d-4 # Tolerance in maximum difference
# between input and output DM
DM.NumberPulay 3 # Number of SCF steps between pulay
mixing
# Eigenvalue problem: order-N or diagonalization
SolutionMethod diagon # OrderN or Diagon
ElectronicTemperature 5 K # Temp. for Fermi smearing
# Molecular dynamics and relaxations
MD.TypeOfRun FC # Type of dynamics:
#ElectronicTemperature 30 K # Temp. for Fermi smearing
#MD.NumCGsteps 40
# Output options
WriteCoorInitial
WriteCoorStep
WriteForces
WriteKpoints .true.
WriteEigenvalues .false.
WriteKbands .true.
WriteBands .true.
WriteMullikenPop 1 # Write Mulliken Population Analysis
WriteCoorXmol .false.
WriteMDCoorXmol .false.
WriteMDhistory .false.
WriteCoorXmol .false.
# Options for saving/reading information
DM.UseSaveDM # Use DM Continuation files
MD.UseSaveXV .false. # Use stored positions and velocities
MD.UseSaveCG .false. # Use stored positions and velocities
SaveRho # Write valence pseudocharge at the mesh
SaveDeltaRho # Write RHOscf-RHOatm at the mesh
SaveElectrostaticPotential .false. # Write the total elect. pot. at the
#mesh
SaveTotalPotential .false. # Write the total pot. at the mesh
WriteSiestaDim .false. # Write minimum dim to siesta.h and stop
WriteDenchar # Write information for DENCHAR
*
*************************************************************************
