[Pw_forum] Questions about Thermal properties calculation

[Eyvaz Isaev]

Dear Bob, 

--- On Sun, 8/9/09, john Bob <bobjohn.lzu at gmail.com> wrote:
 
> Do you mean, physical meaning of thermal properties calculation for
> "meta-stable" phase still need to be explored. The
> method of calculating these is not so simple ?
> 

Well, some metastable phases have no problems with phonons, i.e. they have no imaginary frequences. Diamond is a good example. In this case no problems with thermal property calculations.

When frequences become imaginary, you will mix Real and Imaginary values, which seems to be meaningless.  Omitting  imaginary frequencies and then integrating of thermal properties one implicitly suppose another, dynamically stable phase.

If you have high temperature phase (like bcc Ti, Zr), you can not avoid  
soft modes. In this case anharmonism plays the main role and phonon-phonon interaction corrects the phonon picture. 
  
> as for my third question : the attached picture can  explain.

Take more q-points and you will have better quality picture.

Please, your affiliation.

Bests,
Eyvaz.