From: Prasad Matukumilli <prasadchoudary@gm...>  20130419 09:21:06
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Dear Dr.Togo, I am trying to generate phonon frequencies and eigen vectors for carbon nanotubes. First by using VASP, optimizing the cnt unitcell *INCAR:: (for optmization)* PREC = Accurate ENCUT = 500 IBRION = 2 ISIF = 3 NSW = 20 NELMIN = 5 EDIFF = 1E08 EDIFFG = 1E08 IALGO = 38 ISMEAR = 0 SIGMA = 0.1 LREAL = .FALSE. ADDGRID = .TRUE. LWAVE = .FALSE. LCHARG = .FALSE. *KPOINTS::* Automatic mesh 0 Gamma 1 1 6 0. 0. 0. *POSCAR::* 1.00000000000000 26.7709663712382984 0.0000003049491385 0.0000000000000000 0.0000003049491385 26.7709663712382984 0.0000000000000000 0.0000000000000000 0.0000000000000000 2.4705311793567239 C 40 Selective dynamics Direct 0.7546485467780638 0.5000534686391198 0.0000000000000000 T T T ...... 0.7532642559871684 0.4733338632097980 0.5000000000000000 T T T *POTCAR::* PAW_PBE C 08Apr2002 (potcar from vasp database for element C) this optimization repeated for several times around 10 times by mv CONTCAR POSCAR then the optimized geometry is used to run vasp with ibrion 5 or 6 where *INCAR is* System = cnt1010 NWRITE = 1 LWAVE = .TRUE. LCHARG = .FALSE. LVTOT = .FALSE. ALGO = Fast ISMEAR = 0 SIGMA = 0.1 PREC = Accurate ENCUT = 500 ISTART = 0 EDIFF = 1E8 ISPIN = 1 NSW = 10 ISIF = 2 IBRION = 5 NFREE = 2 POTIM = 0.015 *KPOINTS *and *POTCAR* are same old files in optimization run As IBRION=5 or 6 writes the frequencies and eigen vectors (at gamma point) in OUTCAR, the last 4 frequencies are printing out as imaginary. 197 f/i 0.000433 198 f/i 0.011354 199 f/i 0.011354 120 f/i 0.065003 I need to avoid this imaginary frequencies. I am aware of your scarce time but I would be grateful if u can help me on this. ********************************** Prasad Matukumilli Research Scholar, Advanced Technology Development Centre, Indian Institute of Technology (IIT) Kharagpur  721302, India ********************************** 
From: Atsushi Togo <atz.togo@gm...>  20130422 08:25:45

Hi, This looks like a VASP question and it is difficult for me to answer. What I can say is only that your crystal structure may be dynamically unstable. Togo On Fri, Apr 19, 2013 at 6:20 PM, Prasad Matukumilli <prasadchoudary@...> wrote: > Dear Dr.Togo, > > > I am trying to generate phonon frequencies and eigen vectors for carbon > nanotubes. First by using VASP, optimizing the cnt unitcell > > INCAR:: (for optmization) > PREC = Accurate > ENCUT = 500 > IBRION = 2 > ISIF = 3 > NSW = 20 > NELMIN = 5 > EDIFF = 1E08 > EDIFFG = 1E08 > IALGO = 38 > ISMEAR = 0 > SIGMA = 0.1 > LREAL = .FALSE. > ADDGRID = .TRUE. > LWAVE = .FALSE. > LCHARG = .FALSE. > > KPOINTS:: > Automatic mesh > 0 > Gamma > 1 1 6 > 0. 0. 0. > > POSCAR:: > 1.00000000000000 > 26.7709663712382984 0.0000003049491385 0.0000000000000000 > 0.0000003049491385 26.7709663712382984 0.0000000000000000 > 0.0000000000000000 0.0000000000000000 2.4705311793567239 > C > 40 > Selective dynamics > Direct > 0.7546485467780638 0.5000534686391198 0.0000000000000000 T T T > ...... > 0.7532642559871684 0.4733338632097980 0.5000000000000000 T T T > > POTCAR:: > PAW_PBE C 08Apr2002 (potcar from vasp database for element C) > > this optimization repeated for several times around 10 times by mv CONTCAR > POSCAR > > then the optimized geometry is used to run vasp with ibrion 5 or 6 > > where INCAR is > System = cnt1010 > NWRITE = 1 > LWAVE = .TRUE. > LCHARG = .FALSE. > LVTOT = .FALSE. > > ALGO = Fast > ISMEAR = 0 > SIGMA = 0.1 > PREC = Accurate > ENCUT = 500 > ISTART = 0 > EDIFF = 1E8 > ISPIN = 1 > > NSW = 10 > ISIF = 2 > IBRION = 5 > NFREE = 2 > POTIM = 0.015 > > KPOINTS and POTCAR are same old files in optimization run > > As IBRION=5 or 6 writes the frequencies and eigen vectors (at gamma point) > in OUTCAR, > the last 4 frequencies are printing out as imaginary. > > 197 f/i 0.000433 > 198 f/i 0.011354 > 199 f/i 0.011354 > 120 f/i 0.065003 > > I need to avoid this imaginary frequencies. > > I am aware of your scarce time but I would be grateful if u can help me on > this. > > > ********************************** > Prasad Matukumilli > Research Scholar, > Advanced Technology Development Centre, > Indian Institute of Technology (IIT) > Kharagpur  721302, India > ********************************** > >  > Precog is a nextgeneration analytics platform capable of advanced > analytics on semistructured data. The platform includes APIs for building > apps and a phenomenal toolset for data science. Developers can use > our toolset for easy data analysis & visualization. Get a free account! > http://www2.precog.com/precogplatform/slashdotnewsletter > _______________________________________________ > Phonopyusers mailing list > Phonopyusers@... > https://lists.sourceforge.net/lists/listinfo/phonopyusers >  Atsushi Togo http://atztogo.github.com/ atz.togo@... 