[Pw_forum] something strange in rutile and anatase calculation

[Eyvaz Isaev]

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
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum