Hello Everyone, I'm trying to calculate the phonon dispersion relation of graphene sheet. In this calculation I get negative frequencies. Please could someone guide me where I'm going wrong?
These are my input files: 1) C2.fdf SystemName graphene SystemLabel C2 NumberOfAtoms 2 LatticeConstant 2.46 Ang %block LatticeVectors 0.86 -0.5 0.0 0.86 0.5 0.0 0.0 0.0 20.0 %endblock LatticeVectors AtomicCoordinatesFormat NotScaledCartesianAng %block AtomicCoordinatesAndAtomicSpecies 0.0 0.0 0.0 1 12.0 1.42 0.0 0.0 1 12.0 %endblock AtomicCoordinatesAndAtomicSpecies SuperCell_1 3 SuperCell_2 3 AtomicDispl 0.04 Bohr BandLinesScale ReciprocalLatticeVectors %block BandLines 1 0.000 0.000 0.000 \Gamma 20 0.500 0.000 0.000 M 20 0.333 -0.333 0.000 K 20 0.000 0.000 0.000 \Gamma %endblock BandLines 2) C2-siesta.fdf # graphene, 2 C in each unit cell # optimize structure(15/06/10/Tue) # cal. FC(16/06/10/Wed) # use ./vibrator to calculate phonon(16/06/10/Wed) SystemName graphene SystemLabel C2 NumberOfSpecies 1 %block ChemicalSpeciesLabel 1 6 C %endblock ChemicalSpeciesLabel PAO.BasisSize DZP XC.functional GGA XC.authors PBE MeshCutoff 200.0 Ry DM.MixingWeight 0.3 DM.NumberPulay 3 DM.Tolerance 1.0d-5 %include FC.fdf First I run the utility fcbuild followed by siesta and then the utility vibrator to get the spectrum. Regards, Juzar Thingna Department of Physics, Center for Computation Science and Engineering, National University of Singapore.
