Dear Jusar, The equilibrium lattice and positions that i sent to you was obtained by LDA. You should do some lattice-relaxation if you want to use GGA. Also you should pay attention to the significant figures. For example you should use 0.33333333333 instead of 0.333. MeshCutoff is also important. Try 300-400.
On Mon, Jul 26, 2010 at 1:41 PM, Juzar Thingna <juza...@gmail.com> wrote: > 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. > -- Mehmet Topsakal (Ph.D. Student) UNAM-Institute of Materials Science and Nanotechnology. Bilkent University. 06800 Bilkent, Ankara/Türkiye Tel: 0090 312 290 3527 ; Fax: 0090 312 266 4365 UNAM-web : www.nano.org.tr
