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[cheti ouarda <cheti2010@gmail.com>]

    

Dear aldo

Merci beaucoup de votre réponse:

CaS crystallize in the NaCl structure at 0 temperature and 0pressure(B1phase) and at 40GPa (good agreement with expt) crystallize in the CsCl structure.

1-The total energy of the b1-type phase and b2-type has been calculated at different primitive cell volume and fitted to the murnaghan equation of state, on the other hand, from (Murnaghan-EOS) the calculated enthalpy as function of pressure  for CaS in b1 and b2 phase induced transition pressure is 40GPa.from b2 phase the volume corresponding the transition pressure is 220 b³    → (a(pt)=6.04 b)

2-in order to calculated the specter phonon at transition pressure in b2 phase , I used  trf2-1.in from the input variable of the lattice constant is 6.04 , so in trf2_1. out  the pressure is not 40 GPa. On the other hand ,for other lattice constant the pressure obtained from (m-eos) different to the imprinted in trf2_1.out.

What I do for example in order to plot frequency vs pressure .what pressure chosen.  

Best regards

2009/12/24 Aldo Humberto Romero <aromero@qro.cinvestav.mx>

Dear Cheti

please, next time provide more info about the calculation you have performed.
Is CaS a Zb? is a Wz? is there any inner coordinates? did you relax the
system
with the same parameters ? did you check the forces and
stresses after relaxation? is there anything different? please provide
more details such
we can try to find out where your problem is.

Best regards

-aldo.

-> I new user with abinitio method :

->
-> 1-I studied the effect of pressure of lattice dynamic  of  CaS, so  I
-> calculated the lattice constant and bulk modulus  used  Murnaghan equation
->  of
-> state. when I calculated the specter of the phonon at  equilibrium lattice
-> ,
-> in trf2_1 the pressure is -4.8 GPa.
->
-> Why the pressure not  0GPa.
->
-> 2- in order to calculated the  frequency vs pressure. from  eos-fit  for
-> example the volume at transition pressure  (40GPa) is (b0) , so when I
-> calculated the specter phonon  in trf2_1.out  the pressure  is 25 GPa.
-> What
-> I do ?
->
-> And what pressure I used to plot the phonon vs pressure.
->
->
->
-> Best regards.

->


--

Prof. Aldo Humberto Romero
CINVESTAV-Unidad Queretaro
Libramiento Norponiente 2000
CP 76230, Queretaro, QRO, Mexico
tel: 442 211 9909
fax: 442 211 9938

email: aromero@qro.cinvestav.mx
       aldorome@gmail.com
www: qro.cinvestav.mx/~aromero