[Pw_forum] About the method to obtain the common tangent for determing the phase transition pressure.

[Stefano Baroni]

On Dec 20, 2010, at 2:07 PM, 红生 赵 wrote:

> Dear all,

Dear Hongsheng,

>  
> For the first-order phase transitions, the following criteria should be met: Pressures of the two phases are equal, i.e.,
> P_{eq} = - \frac{{d{E_1}}}{{d{V_1}}} = - \frac{{d{E_2}}}{{d{V_2}}}
>  
> In other words, the P_{eq} is gradient of common tangent of the two phases E-V curves obtained from EOS fitting.
> This is a mathematical problem, but for the plot of this common tangent, can someone please give me some hints? What tools/softwares should I use for this purpose? Thanks in advance.

1) plot the curves and find the tangent by hand
2) solve the equation E1(V1(p))+pV1(p)=E2(V2(p))+pV2(p), as a function of the pressure p. V12 is here the volume of the two phases as a function of the pressure.

hope this helps
Stefano

PS: in the future, please do not forget to include your affiliation with your signature

>  
> Best regards.
> Hongsheng Zhao
> 
>  _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum

---
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

Please, if possible, don't  send me MS Word or PowerPoint attachments
Why? See:  http://www.gnu.org/philosophy/no-word-attachments.html







-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.democritos.it/pipermail/pw_forum/attachments/20101220/859343d9/attachment.htm