[Pw_forum] something strange in rutile and anatase calculation

[vega]

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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