[Pw_forum] fqha.x

[Eyvaz Isaev]

Hi again,

I found the fqha.f90 code on the forum and compiled it with mpif77 to get the executable. 

It is not the same I have been talking about, but it does not matter in this particular case. 
Besides, there is no need to compile it using mpif77 or mpif90. Use just a serial version.
 
I am not a physics major, so I don't understand the code completely. 

In this case you will meet lots of troubles. I think it is worth reading some general purpose  textbook  on solid state physics. As example, textbook by Kittel, or Aschroft and Mermin, or  Harrison, or Martin, or Marder  etc.

So, I have a question - please excuse me if it is grossly incorrect. I expect the free energy F to 
equal E at zero temperature. But, the F I obtain from the code is positive at T=0 and becomes negative at larger T. Could you please explain this?

According to quantum-mechanical principles atoms in solid states are not frozen at T=0K, but vibrate due to the uncertinity principle of the quantum mechanics, so there is so called zero vibration energy which is positive by its definition (for a stable structure all frequences are positive). At higher T the phonon contribution to the free energy becomes negative.

Bests,
Eyvaz. 


Thanks,
Shriram

Eyvaz Isaev wrote:
> Hi Shrihram,
>  
>   I'm facing some trouble running this program and hope someone can help 
> me out. I'm using the dos file generated in example 06 to calculate the 
> free energy. But, when I give the input to fqha.x as alas.phdos, for any 
> temperature, the free energy turns out to be zero. I'm not sure what is 
> going wrong here. Can someone please help?
>
> The answer is quite simple: as usual \omega(1) =0, and dos(1)=0, so, you can not 
> calculate  \ln(2sinh(\hbar\omega/2kT)). The starting point has to be 2.
>
> But I think if you find QHA code sent to the forum you will gain much more.
>
> Bests,
> Eyvaz.
>
>
> Thanks,
> Shriram
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