[Pw_forum] phonon at Gamma point
Eyvaz Isaev
eyvaz_isaev at yahoo.com
Thu Aug 24 16:05:48 CEST 2006
Hi,
> I just relaxed Anatase TiO2 with *ibrav= 7 , *
> then output gave that Only 8 symmetry Operations are
> found.
Because of that your setup is not consistent.
Your lattice parameter is
7.1356*0.529177=3.7759954012, but 2 Oxygen atoms have
X-component (in units of alat) of 0.5.
You put 1.888, but, 1.888 is not equal
3.7759954012/2=1.8879977. So, they could not be
considered the same within 10^{-6} which is a default
mismatch (please correct me if I am wrong). For sure
you have to use 7 digits (after point) in such a kind
specific cases, as c/a, b/a (and cosines, presumably).
Besides, your atomic positions are completely
different of these specified in
http://cst-www.nrl.navy.mil/lattice/struk.xmol/c5.pos
Please use lattice parameters and atomic coordinates
(in Angstrom) as they are in the link, and report what
happens.
I am not sure that it is a good idea to relax a well
known structure if you have a problem with its
symmetry.
Bests,
Eyvaz.
> According to your mail, this structure should have
> 16 Symmetry Operations,
> so
> how can i obtain correct symmetry operations ?
>
> Input file is below , thank you in advance !
>
>
> *&CONTROL
> title = 'TiO2' ,
> calculation = 'relax',
> verbosity = 'default',
> tprnfor = .true.,
> outdir = '/home/haiping/tmp/',
> prefix = 'tio2-1',
> disk_io = 'default',
> nstep = 200,
> pseudo_dir =
> '/home/haiping/espresso/pseudo/',
> /*
>
> *&SYSTEM
> ibrav= 7,
> celldm(1)=7.1356,celldm(3)=2.51218,
> nat = 6 ,
> ntyp = 2 ,
> nbnd = 30 ,
> ecutwfc = 30.0000000000,
> occupations = 'fixed' ,
> *
>
> *&ELECTRONS
> electron_maxstep = 100,
> conv_thr = 1.0e-09,
> mixing_mode = 'plain' ,
> startingpot = 'atomic' ,
> startingwfc = 'atomic' ,
> mixing_beta = 0.300000000,
> mixing_ndim = 8,
> diagonalization = 'david_overlap' ,
> diago_david_ndim = 8,
> /*
>
> *&IONS
> ion_dynamics = 'bfgs',
> pot_extrapolation = 'first_order',
> wfc_extrapolation = 'first_order',*
>
> */*
>
> *O 15.999 O.pw91-van_ak.UPF
> Ti 47.867 Ti.pw91-nsp-van.UPF
> ATOMIC_POSITIONS angstrom
> Ti 0.000000000 0.000000000 0.000000000
> Ti 0.000000000 1.888000000 2.371500000
> O 0.000000000 0.000000000 -1.983097630
> O 0.000000000 0.000000000 1.983097630
> O 0.000000000 1.888000000 0.387796645
> O 0.000000000 1.888000000 4.355203355
> K_POINTS automatic
> 6 6 7 0 0 0
> *
> *
>
> * On 8/20/06, Eyvaz Isaev <eyvaz_isaev at yahoo.com>
> wrote:
> >
> > OK, let me hint more.
> >
> > Anatase has a Pearson symbol tI12 or space group
> > I4_1/amd. So, ibrav should be 7, but you have
> chosen a
> > monoclinic lattice, i.e. ibrav=14. The space group
> has
> > 16 symmetry elements, but your choice after
> correcting
> > ecutrho gives only 4 symmetry elements .
> >
> > Imagine FCC lattice and its conventional basis
> > vectors now. According to you now we have to put
> > ibrav=4 or 5. But ibrav=2 for FCC lattice.
> >
> > In addition, I also checked your input file via
> > XCrysDen before I replied previously. Yes, there
> is no
> > problem with it, but a figure does not look like
> > anatase though you used nonzero ibrav. XcrysDen
> > usually replicates atomic positions if
> ibrav.neq.0.
> > For example, if you put ibrav=0 for FCC cell and
> > specify conventional CELL_PARAMETERS you will find
> a
> > rhombohedron, but using ibrav=2 and default basis
> > vectors you find a cubic cell.
> >
> > Bests,
> > Eyvaz.
> >
> >
> > --- lan haiping <lanhaiping at gmail.com> wrote:
> >
> > > Dear Eyvaz,
> > > Thank you.
> > > I checked the strcuture again using XCRYSDEN,
> > > and found no problems related to the lattices.
> > >
> > > Regards,
> > >
> > > Hai-Ping
> > >
> > >
> > >
> > > On 8/20/06, Eyvaz Isaev <eyvaz_isaev at yahoo.com>
> > > wrote:
> > > >
> > > > Hi,
> > > >
> > > > It seems your lattice choice is not correct.
> > > Please
> > > > have a look at
> > > >
> http://cst-www.nrl.navy.mil/lattice/struk/c5.html
> > > >
> > > > Bests,
> > > > Eyvaz.
> > > >
> > > > --- lan haiping <lanhaiping at gmail.com> wrote:
> > > >
> > > > > Dear All,
> > > > > I also have calculated gamma phonon
> frequencies
> > > of
> > > > > anatase TiO2 .
> > > > > I run ph.x caculation after relaxing the
> > > structure,
> > > > > but 9 of 18 frequencies
> > > > > are minus.
> > > > >
> > > > > Would you please give me some hints and
> help?
> > > > >
> > > > > input settings are below, thank you in
> advance !
> > > > >
> > > > > *phonons of TiO2 at Gamma
> > > > > &inputph
> > > > > tr2_ph=1.0d-14,
> > > > > recover=.true.,
> > > > > epsil=.true.,
> > > > > prefix='tio2',
> > > > > fildyn='TiO2-gamma.dyn',
> > > > > outdir='/home/haiping/tmp/'
> > > > > /
> > > > > 0.0 0.0 0.0*
> > > > > **
> > > > > *Relaxing calculation input :*
> > > > > *&CONTROL
> > > > > title = 'TiO2' ,
> > > > > calculation = 'relax',
> > > > > verbosity = 'default',
> > > > > tprnfor = .true.,
> > > > > outdir = '/home/haiping/tmp/',
> > > > > prefix = 'tio2',
> > > > > disk_io = 'default',
> > > > > nstep = 200,
> > > > > pseudo_dir =
> > > > > '/home/haiping/espresso/pseudo/',
> > > > > /
> > > > > &SYSTEM
> > > > > ibrav= 14,
> > > > >
> > > > >
> celldm(1)=10.2856,celldm(2)=1.0,celldm(3)=1.0,
> > > > >
> > > > > celldm(4)=-0.759357,celldm(5)=-0.759357,
> > > > > celldm(6)=0.518714
> > > > > nat = 6 ,
> > > > > ntyp = 2 ,
> > > > > nbnd = 30 ,
> > > > > ecutwfc = 30.0000000000,
> > > > > ecutrho = 160.000,
> > > > > occupations = 'fixed' ,
> > > > > /
> > > > >
> > > > >
> > > > > &ELECTRONS
> > > > > electron_maxstep = 100,
> > > > > conv_thr = 1.0e-07,
> > > > > mixing_mode = 'plain' ,
> > > > > startingpot = 'atomic' ,
> > > > > startingwfc = 'atomic' ,
> > > > > mixing_beta = 0.300000000,
> > > > > mixing_ndim = 8,
> > > > > diagonalization = 'david_overlap' ,
> > > > > diago_david_ndim = 8,
> > > > > /
>
=== message truncated ===
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