Dear siesta user, I am doing phonon calculation of carbon nanotube using siesta. But I am getting negative frequencies for more than half of the calculated frequencies. I wanted to know reason for getting negative frequencies of my calculation.
I have optimized the structure using MD.MaxForceTol 0.001 eV/Ang And condition for scf are as follows DM.Tolerance 0.5d-4 DM.Require.Energy.Convergence true DM.Energy.Tolerance .5d-4 eV My input file for type of run- FC ---- SystemName Phonon calculation # Descriptive name of the system SystemLabel Phonon_fc # Short name for naming files # Output options LongOutput false # Species and atoms %block ChemicalSpeciesLabel 1 6 C %endblock ChemicalSpeciesLabel NumberOfSpecies 1 WriteKpoints true PAO.Basis<basis.fdf LatticeConstant 1 Ang Messcutoff 150 Ry Kgridcutoff 10.0 Ang xc.functional GGA xc.authors PBE DM.UseSaveDM true MaxSCFIterations 500 DM.MixingWeight 0.25 DM.NumberPulay 4 DM.Tolerance 0.4d-4 DM.Require.Energy.Convergence true DM.Energy.Tolerance .5d-4 eV #Atomic coordinates %include PhononFC.fdf AtomicCoordinatesFormat Fractional Thanking You. __________________ Saikat Paik IIT Kanpur UP,India
