[Pw_forum] something strange in rutile and anatase calculation

[vega]

Dear sir,

thank you for your time. Now I'm more clear about the matter.

best wishes,

vega


=================================================================================
Vega Lew (weijia liu)
PH.D Candidate in Chemical Engineering
State Key Laboratory of Materials-oriented Chemical Engineering
College of Chemistry and Chemical Engineering
Nanjing University of Technology, 210009, Nanjing, Jiangsu, China

--------------------------------------------------
From: "Eyvaz Isaev" <eyvaz_isaev at yahoo.com>
Sent: Friday, August 29, 2008 11:23 PM
To: "PWSCF Forum" <pw_forum at pwscf.org>
Subject: Re: [Pw_forum] something strange in rutile and anatase calculation

> 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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>> >> >
>> >> >
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