[Pw_forum] Consideration of Temperature in equilibrium system(T=0, P=0)

[bramha pandey]

Dear Dr. Stefano and Dr. Nicola Marzari thanks for your quick reply.
Actualy i have calculated the Helmholtz free energy (F) which is given as

F(V, T) = E0(V) + Fvib (V, T).

The Fvib(V, T) is calculated by PH/fqha.x utility and E0(V) is the
equilibrium ground state energy which is calculated by pw.x.
it is stated in a research paper>>>>For a given T and V, the equilibrium
state of the crystal
is determined by minimising F with respect to all possible
degrees of freedom. The equation of state (pressure (P) versus
V) of the system is obtained by equating P to minus the
derivative of F with respect to V at constant T, or P = − (∂F/∂V)T <<<<<<

Sir i was tried for QHA package in QE as given paper
http://arxiv.org/abs/1112.4977v1 , it is using the QHA pakage which is not
well understood by me and also this was giving wrong result but  it was ok
with PH/fqha.x.
Please show me the ray of light regarding Helmholtz free energy (F) which
is the base root of all thermodynamics property describe by one paper
http://iopscience.iop.org/0953-8984/24/3/035401 for your kind reference.

Any comment in any form is appreciable.





2012/3/24 Nicola Marzari <nicola.marzari at epfl.ch>

>
> Here it is:
>
> http://arxiv.org/abs/1112.**4977v1 <http://arxiv.org/abs/1112.4977v1>
> Thermal properties of materials from ab-initio quasi-harmonic phonons
> Stefano Baroni, Paolo Giannozzi, Eyvaz Isaev
>
>                        nicola
>
>
>
> On 24/03/2012 05:35, bramha pandey wrote:
>
>> Dear All,
>> I want to incorporate the temperature effect in my calculation. As i
>> know for this purpose firstly i have to compute the free energy and then
>> this free energy is added to the ground state total energy(T=0,P=0).
>> then by the equation of state we have to find out the lattice parameter.
>> But i am wonder if i am trying to fit eos, it will give the equilibrium
>> lattice parameter not the temperature dependent lattice parameter.
>> Please let me know whether i am proceeding wrong way if so then how can
>> i obtained my lattice parameter which is dependent upon temperature?
>> Any type of help is highly appreciable .
>>
>> --
>> Thanks and Regards
>> Bramha Prasad Pandey
>> GLA University, Mathura.
>> INDIA.
>>
>>
>>
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>>
>
>
> --
>
> ------------------------------**------------------------------**----------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
>



-- 
Thanks and Regards
Bramha Prasad Pandey
GLA University, Mathura.
INDIA.
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