[Pw_forum] phonon at Gamma point
lan haiping
lanhaiping at gmail.com
Sat Aug 26 22:02:32 CEST 2006
Dear stefano,
Thank you. I think i catch this indication..
regards,
Hai-Ping
On 8/27/06, Stefano Baroni <baroni at sissa.it> wrote:
>
> Hai-Ping: forgive my poor understanding of you progresses, but let me
> just you a very simple hint. In order for the program to be able to detect a
> symmetry operation, it is necessary that the fractional translation
> associated with it can be represented on the discrete FFT grid. As simple as
> that. Best wishes - Stefano
>
> On Aug 26, 2006, at 6:57 PM, lan haiping wrote:
>
> Dear Eyvaz,
>
> Thank you for this instructions!
>
> I just tried the coordinates from NRL-weblink, and didnot find any
> problems as before.
>
> But i have another problem want to ask you , which is just a result that
> i wanna finish
> Stefano's exercise assigned last mail.
>
> I just found that inversion symmetry would not found by pw.x code when the
> FFT grds are not compatable with fractional translation. Then, I tried to
> mannually set fft grid by nr1,nr2,nr3 .
> Take$(espresso) /examples/example02/si.scf.in for example, when *ecutwfc*is
> 18.0Ry, the pw.x would found all Sym Ops, with smallest FFT grids
> (20,20,20). But when *ecutwfc* is set to 30.0Ry with (30,30,30) fft grids
> default, the code gave ""warning: symmetry operation # N not allowed".
> According to mannual, this warning is mostly related to fractional
> translation incompatable with the fft grids. So, i tried to reset fft grid
> respectly with (36,36,36), (40,40,40),(60,60,60) and (54,54,54) , no such
> warning messages are given for the first 3 situation but same occurs for the
> last fft grids. I cannot understand this test results, since the userguide
> states that this warning is due to" *FFT grid dimension along that
> direction is not divisible respectively by 2 or by 3, the symmetry operation
> will not transform the FFT grid into itself*" . Obviously, all grids
> dimension along x/y/z direction can be divided by 2 or 3.
> My understanding is correct or not ?
>
>
>
> Regards,
> Hai-Ping
>
>
>
>
>
>
>
>
> On 8/24/06, Eyvaz Isaev <eyvaz_isaev at yahoo.com > wrote:
> >
> > 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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>
> ---
> Stefano Baroni - SISSA & DEMOCRITOS National Simulation Center - Trieste
> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)
>
> Please, if possible, don't send me MS Word or PowerPoint attachments
> Why? See: http://www.gnu.org/philosophy/no-word-attachments.html
>
>
>
>
>
>
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