Dear Paolo,

Thanks very much for your help. But this does'nt solve my problem. I know there 
are

-Murnagham EOS
-Second order Birch-Murnagham EOS
-Third order Birch-Murnagham EOS

Please I would like you to have a look at the ev. f90 file in pwtools folder 
and from the way the EOS are? written, to identify the meaning of the following 
EOS in this file:

-Birch 1
-Birch 2

Do they mean:

-Second order Birch-Murnagham 
-Third order Birch-Murnagham? ?

In which case we should not lead to a value of B' for second order(usally equal 
to 4 for this EOS).

Does the Murnagham in this file has the same meaning as in the page 
?http://en.wikipedia.org/wiki/Birch?Murnaghan_equation_of_state? ?


Your answer is of great help for me. Thanks in advance.

*******************************
Bertrand SITAMTZE YOUMBI
Laboratory of material sciences
Department of Physics
University of Yaound? I-Cameroon
*****************************

--- En date de?: Lun 15.2.10, Paolo Giannozzi <giannozz at democritos.it> a 
?crit?:

De: Paolo Giannozzi <giannozz at democritos.it>
Objet: Re: [Pw_forum] Fw : Help on ev.x procedures!!!
?: "PWSCF Forum" <pw_forum at pwscf.org>
Date: Lundi 15 f?vrier 2010, 15h49

Bertrand SITAMTZE wrote:

>? Please can somebody help in giving the four EOS use in this file?

most of what you need is here:
???http://en.wikipedia.org/wiki/Birch?Murnaghan_equation_of_state

> What is the unit of the fitting pressure in this file?

I think it is KBar

> Is it correct to have negative pressure?

for expanded systems (V > V_0), it is

P.
-- 
Paolo Giannozzi, Democritos and University of Udine, Italy
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