[Pw_forum] enthlapy of a system

[Matteo Cococcioni]

Dear Bipul

I think all you need to do is computing the equation of state for both 
phases. In other words you choose a series of lattice parameters (that
may be different for the two phases) and compute the total energy for 
each of them. In this case for B1 (NaCl) and B2 (CsCl) you don't need to 
relax the atomic positions for each lattice parameter as you would do in 
general. Once you get E(V) for each of the phase, you can use the 
program ev.x to fit a Murnaghan or a Birch eq. of state in your data. 
 From the equation of state you have chosen you can compute the 
derivative P=-dE/dV at any V within the interval of your fit. This will 
be the pressure on your system. for every value of P
you will have V and the corresponding E so you will be able to construct 
E+PV (enthalpy) for the values of P you have.

hope this helps,

Matteo




Bipul Rakshit wrote:
> Hello Everyone,
> I want to calculate the enthlapy at different pressures of ScAs in B1 
> and B2 phase, so that i able to find the transition pressure. Can 
> anybody tell me the correct method to do that?
>
>
> -- 
> Bipul Rakshit
> PhD Student,
> Barkatullah University,
> Bhopal 462026,
> MP, India
> ------------------------------------------------------------------------
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
> http://www.democritos.it/mailman/listinfo/pw_forum
>