[Pw_forum] something strange in rutile and anatase calculation

[Nicola Marzari]

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

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Prof Nicola Marzari   Department of Materials Science and Engineering
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