[Pw_forum] something strange in rutile and anatase calculation

Eyvaz Isaev eyvaz_isaev at yahoo.com
Fri Aug 29 17:23:30 CEST 2008 

Dear Vega,

--- On Fri, 8/29/08, vega <vegalew at hotmail.com> wrote:

> How could you get the relationship between the free 
> energy and volume? Do you mean that you changed the
> cell volume sequentially and make a scf 
> calculation to gain the free energies for the certain
> volume? the cell volume was grown bit by bit as 
> your will, then the scf calculation did accordingly?
> 

We calculated total energy and phonons (then free energy) for a given set of volumes.

> and how could you get the volume as a function of > pressure as fig.2 shown? 
> what kind of QE calculation could deal with it?
> 
If you set up tstress=.true. you can find what is a stress (and pressure) in your system. Again, for a given set of the unit cell volumes. Sometime only a SCF calculation is enough, but sometime, especially for non-cubic systems, you can fix pressure and relax your system. 

Bests,
Eyvaz.

> vega
> 
> --------------------------------------------------
> From: "Eyvaz Isaev" <eyvaz_isaev at yahoo.com>
> Sent: Friday, August 29, 2008 9:00 PM
> To: "PWSCF Forum" <pw_forum at pwscf.org>
> Subject: Re: [Pw_forum] something strange in rutile and
> anatase calculation
> 
> > Dear Vega,
> >
> 
> > On the left side (under pressure) first DHCP has the
> lowest energy, then 
> > hcp, and finally, FCC phase is the lowest in energy.
> So, we stated, there 
> > are DHCP --> HCP and HCP --> FCC phase
> transitons
> >
> > Hope this helps.
> >
> > Bests,
> > Eyvaz
> >
> >
> -------------------------------------------------------------------
> > Prof. Eyvaz Isaev,
> > Theoretical Physics Department, Moscow State Institute
> of Steel & Alloys, 
> > Russia,
> > Department of Physics, Chemistry, and Biology (IFM),
> Linkoping University, 
> > Sweden
> > Condensed Matter Theory Group, Uppsala University,
> Sweden
> > Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se,
> eyvaz_isaev at yahoo.com
> >
> >
> > --- On Thu, 8/28/08, vega <vegalew at hotmail.com>
> wrote:
> >
> >> From: vega <vegalew at hotmail.com>
> >> Subject: Re: [Pw_forum] something strange in
> rutile and anatase 
> >> calculation
> >> To: eyvaz_isaev at yahoo.com, "PWSCF Forum"
> <pw_forum at pwscf.org>
> >> Date: Thursday, August 28, 2008, 6:05 PM
> >> Dear Eyvaz,
> >>
> >> I have read your PNAS paper just now. I'm very
> >> interesting about the phase
> >> transition mentioned in your paper. But because of
> lack of
> >> experience in
> >> your scopes, I'm not very clear about the
> detail of the
> >> calculations of
> >> phase transitions.
> >> In the second paragraph of Results and Discussion
> section,
> >> you said
> >> 'According to
> >> our free-energy calculations, there exist two
> phase
> >> transitions in the FeH
> >> system...'. How did you simulated the two
> phase
> >> transitions? How could you
> >> calculate the Volume as a function of Pressure as
> shown in
> >> Fig. 2? The line
> >> in Fig. 2 went quite smoothly, so you may not plot
> it point
> >> by point. How
> >> could you get the line?
> >>
> >> thank you for reading
> >>
> >> vega
> >>
> >>
> >> --------------------------------------------------
> >> From: "Eyvaz Isaev"
> <eyvaz_isaev at yahoo.com>
> >> Sent: Thursday, August 28, 2008 9:25 PM
> >> To: "PWSCF Forum"
> <pw_forum at pwscf.org>
> >> Subject: Re: [Pw_forum] something strange in
> rutile and
> >> anatase calculation
> >>
> >> > Dear Vega,
> >> >
> >> > Please be not so official. I add
> (automatically) my
> >> affiliation due to our
> >> > accepted Netetiquette.
> >> >
> >> > Bests,
> >> > Eyvaz.
> >> >
> >> >
> >>
> -------------------------------------------------------------------
> >> > Prof. Eyvaz Isaev,
> >> > Theoretical Physics Department, Moscow State
> Institute
> >> of Steel & Alloys,
> >> > Russia,
> >> > Department of Physics, Chemistry, and Biology
> (IFM),
> >> Linkoping University,
> >> > Sweden
> >> > Condensed Matter Theory Group, Uppsala
> University,
> >> Sweden
> >> > Eyvaz.Isaev at fysik.uu.se, isaev at ifm.liu.se,
> >> eyvaz_isaev at yahoo.com
> >> >
> >> >
> >> > --- On Thu, 8/28/08, vega
> <vegalew at hotmail.com>
> >> wrote:
> >> >
> >> >> From: vega <vegalew at hotmail.com>
> >> >> Subject: Re: [Pw_forum] something strange
> in
> >> rutile and anatase
> >> >> calculation
> >> >> To: eyvaz_isaev at yahoo.com, "PWSCF
> Forum"
> >> <pw_forum at pwscf.org>
> >> >> Date: Thursday, August 28, 2008, 5:08 PM
> >> >> Thank you for Prof. Eyvaz Isaev's
> hints
> >> >> I'll read the excellent article as
> your
> >> suggestion.
> >> >> It's really nice of you.
> >> >>
> >> >> vega
> >> >>
> >> >>
> --------------------------------------------------
> >> >> From: "Eyvaz Isaev"
> >> <eyvaz_isaev at yahoo.com>
> >> >> Sent: Thursday, August 28, 2008 8:58 PM
> >> >> To: "PWSCF Forum"
> >> <pw_forum at pwscf.org>
> >> >> Subject: Re: [Pw_forum] something strange
> in
> >> rutile and
> >> >> anatase calculation
> >> >>
> >> >> > Hi,
> >> >> >
> >> >> > One more suggestion.
> >> >> > As far as I know the same situation
> is for
> >> \alpha
> >> >> and \omega phases of Ti,
> >> >> > as well as HCP and DHCP phases of
> FeH. But
> >> free energy
> >> >> calculations have
> >> >> > shown than \alpha-Ti  and DHCP
> FeH are
> >> stabilized
> >> >> due to the phonon
> >> >> > contribution.
> >> >> > For FeH you can see: Eyvaz I. Isaev
> et al.,
> >> Dynamical
> >> >> stability of Fe-H in
> >> >> > the Earth's mantle and core
> regions,
> >> Proceedings
> >> >> of the National Academy
> >> >> > of Sciences of the USA (PNAS), 104
> (22), 29
> >> May 2007,
> >> >> 9168. PNAS Special
> >> >> > Issue "Geophysics".
> >> >> >
> >> >> > So, you can try follow this way, if
> you like.
> >> >> >
> >> >> > Bests,
> >> >> > Eyvaz.
> >> >> >
> >> >> >
> >> >> >
> >> >>
> >>
> -------------------------------------------------------------------
> >> >> > Prof. Eyvaz Isaev,
> >> >> > Theoretical Physics Department,
> Moscow State
> >> Institute
> >> >> of Steel & Alloys,
> >> >> > Russia,
> >> >> > Department of Physics, Chemistry,
> and Biology
> >> (IFM),
> >> >> Linkoping University,
> >> >> > Sweden
> >> >> > Condensed Matter Theory Group,
> Uppsala
> >> University,
> >> >> Sweden
> >> >> > Eyvaz.Isaev at fysik.uu.se,
> isaev at ifm.liu.se,
> >> >> eyvaz_isaev at yahoo.com
> >> >> >
> >> >> >
> >> >> > --- On Thu, 8/28/08, Nicola Marzari
> >> >> <marzari at MIT.EDU> wrote:
> >> >> >
> >> >> >> From: Nicola Marzari
> >> <marzari at MIT.EDU>
> >> >> >> Subject: Re: [Pw_forum]
> something strange
> >> in
> >> >> rutile and anatase
> >> >> >> calculation
> >> >> >> To: "PWSCF Forum"
> >> >> <pw_forum at pwscf.org>
> >> >> >> Date: Thursday, August 28, 2008,
> 3:01 PM
> >> >> >> vega wrote:
> >> >> >> > Dear all,
> >> >> >> >
> >> >> >> > It is known that the rutile
> is more
> >> stable
> >> >> than
> >> >> >> anatase in
> >> >> >> > thermodynamics.
> Surprisingly, when I
> >> did the
> >> >> vc-relax
> >> >> >> calculation by
> >> >> >> > QE, I found the calculated
> energy of
> >> anatase
> >> >> lower
> >> >> >> than rutile. Both
> >> >> >> > vc-relax calculation for
> rutile and
> >> anatase
> >> >> onverged
> >> >> >> in 6 scf cycles and
> >> >> >> > 3 bfgs steps, giving the
> final
> >> enthalpy =
> >> >> >> -362.7585836890 Ry for rutile
> >> >> >> > and -725.5447425835 Ry for
> antase.
> >> So the
> >> >> average
> >> >> >> energy of [TiO2] unit
> >> >> >> > is -181.3792918445 Ry for
> rutile and
> >> >> -181.386185645875
> >> >> >> Ry for anatase.
> >> >> >> > It looks like anatase is
> more stable
> >> than
> >> >> rutile. Do
> >> >> >> you think it was
> >> >> >> > quite strange?
> >> >> >>
> >> >> >>
> >> >> >> Dear Vega,
> >> >> >>
> >> >> >> your results are probably
> correct.
> >> It's a
> >> >> known failure
> >> >> >> of LDA and GGA
> >> >> >> to stabilize anatase more than
> rutile.
> >> >> >>
> >> >> >> nicola
> >> >> >>
> >> >> >> -- 
> >> >> >>
> >> >>
> >>
> ---------------------------------------------------------------------
> >> >> >> Prof Nicola Marzari   Department
> of
> >> Materials
> >> >> Science and
> >> >> >> Engineering
> >> >> >> 13-5066   MIT   77 Massachusetts
> Avenue
> >> >> Cambridge MA
> >> >> >> 02139-4307 USA
> >> >> >> tel 617.4522758 fax 2586534
> >> marzari at mit.edu
> >> >> >> http://quasiamore.mit.edu
> >> >> >>
> >> _______________________________________________
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> >> >> >
> >> >> >
> >> >> >
> >> >> >
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