[Pw_forum] Phase Transition Pressures

[Stefano Baroni]

Dear Huolin: as explained in my previous post, I beg to differ. Phonons have nothing to do with the question asked by Cecil, as long as the temperature is low enough. Even less, the electronic entropy, as long as the the system insulating (even in metals, the electronic entropy play a very little role, below the Farmi temperature which is typically several thousands degrees ...). Even considering temperature effects, it is not the "free energy" that has to be made equal (usually, one indicates with this term the Helmholts free energy, E-TS), but the "Gibbs free energy" (E-TS+PV). Hope this clarifies a bit ... SB

On Apr 18, 2010, at 3:04 PM, Huolin Xin wrote:

> You'll need phonon entropy and electronic entropy as well. Free energy is E-TS. The transition pressure is where the free energy of the two structures are the same. 
> 
> On Sun, Apr 18, 2010 at 5:39 AM, naphtaly moro <moronaphtaly84 at gmail.com> wrote:
> Dear all,
> 
> I am working on the pressure induced phase transitions of GaAs, I have
> already obtained, the respective EV data for the structures and want
> to get the transition pressures for the structures, Any advice on how
> this can be done in Espresso?
> 
> Thanks
> Cecil Naphtaly Moro,
> Mphil. Student,
> Department of Physics,
> Moi University, Chepkoilel Campus,
> Kenya
> 
> --
> Cecil Naphtaly Moro
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
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