[Pw_forum] Phase Transition Pressures

[Huolin Xin]

Stefano, thanks a lot for pointing my mistake out. In the entropy term,
besides phonon and electronic entropy, how to calculate the structural
entropy?

On Sun, Apr 18, 2010 at 9:25 AM, Stefano Baroni <baroni at sissa.it> wrote:

> 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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