[Pw_forum] phonon at Gamma point

Stefano Baroni baroni at sissa.it
Sat Aug 26 19:02:36 CEST 2006


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)

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