[Pw_forum] something strange in rutile and anatase calculation

vega vegalew at hotmail.com
Fri Aug 29 15:22:27 CEST 2008 

Dear sir,

thank you for your so kindly explanation. I also have some questions about 
your article.

> As you can see we considered three FeH phases (FCC, HCP, and DHCP) and 
> plotted their free energies including phonon contribution with respect to 
> the unit cell volume.

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?

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?

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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