PHONON

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nulakani · #1 Post by **nulakani** » Thu Apr 17, 2014 8:49 am

Dear Vasp Users

Here anybody familier with phonon band dispersion of graphene, I am trying to plot it from the last one month but it always giving -ve freq near Gamma point. which tags will affect the results more ?

I did optimization with following incar with a 64x64x1 KPOINT set

PREC = High
ENCUT = 520
IBRION = 2
NSW = 100
ISIF = 3
ALGO = Normal (blocked Davidson)
NELM = 60
NELMIN = 5
EDIFF = 1.0e-010
EDIFFG = -0.0001
VOSKOWN = 1
NBLOCK = 1
ISPIN = 1
INIWAV = 1
ISTART = 0
ICHARG = 2
LWAVE = .FALSE.
LCHARG = .FALSE.
ADDGRID = .TRUE.
ISMEAR = 1
SIGMA = 2.000000e-01
LREAL = .FALSE.
RWIGS = 0.77
NPAR = 1

and I used phonopy code and generate 6x6x1 supercell and run a singlepoint calculation for generated poscar

Still iam getting -ve freq . can any one plz help me in this case how can i proceed furthur to resolve this PROB

?

#2 Post by **admin** » Wed Apr 23, 2014 9:06 am

-ve freq is not an output of the standard version of VASP, please contact the MaterialsDesign support

kmkumar · #3 Post by **kmkumar** » Thu Jun 05, 2014 1:54 pm

I have a similar problem. Structure optimized to the difference of e-10 and calculated the phonon frequencies. But still end up with the feeble imaginary frequencies and it is reflected also in the Phonon dos. Any help would be appreciated.