[Pw_forum] Fw : ev.x procedures

[Ngoc Linh Nguyen]

Bertrand SITAMTZE wrote:
>
>
>     As I know, scf and nscf in pw.x are with zero pressure (please
>     correct me if I am wrong).
>
May be the external pressure (like pressures of experimental conditions) 
is zero, but the internal pressure that is reduced by the force field in 
system is not zero at all.

The basic formula for pressure can be referred in the book Molecule 
Simulation of Daan Frenkel and Smit Berend.
 
>
>     Thus, when evaluating the EOS parameters with ev.x, the code uses
>     the E vs VOLUME data to evaluate the bulk modulus throught the
>     second derivative. But, how does the code proceed in order to
>     evaluate the pressure derivative of the bulk modulus K', without
>     varing the pressure? If otherwise, can somebody tell me the range
>     of pressure used to evaluate K'?
>
>     Please, note that K' is defined as K'=(dK/dP) at P=0.
>
The values of pressures will be fitted with Equation of State (EOS) and 
we can have first and second derivatives easily

Linh
>
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