[Pw_forum] Fwd: phonon instability

[bhabya sahoo]

---------- Forwarded message ----------
From: Stefano Baroni <baroni at sissa.it>
Date: Tue, Aug 23, 2011 at 12:15 PM
Subject: Re: [Pw_forum] phonon instability
To: PWSCF Forum <pw_forum at pwscf.org>



On Aug 23, 2011, at 8:40 PM, bhabya sahoo wrote:

sir


???

i am calculating the phase transition of some carbides
the transition from B1 to B2 transition occures at 130 gpa by enthalpy
compparison


OK

but i am able to find phonon instability at 130 gpa for B1 structure


you mean, a phonon (which mode?) goes soft at the same pressure at which the
enthalpies of the two phase coincide?
TA branch in the  gamma -X-R  directions for B1 phase

-

but at the same time i am not able to find the dyanamic stability of B2
phase at 130 gpa


???

but it occures high pressure (more than130 gpa )


???

is there any explanation for this ?


explanation for WHAT? why the phonon instability occures at 130 gpa for B2
strcuture in the gamma -x directions for B2 structure although it is
thermodyanamical stable by enthalpy comparison

what are you talking about? may we expect a somewhat more well thought and
articulate question?

is there any relation of thermodyanamical unstability

and dyanamical unstability simultaneously?


???

answers are highly appriceted with some reson


well-thought and well documented questions questions would be even more
appreciAted for any reAson ...

SB

---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni
(skype)

La morale est une logique de l'action comme la logique est une morale de la
pensée - Jean Piaget


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