[Pw_forum] something strange in rutile and anatase calculation

[vega]

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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