[Pw_forum] fqha.x

[Katalin Gaal-Nagy]

Dear Shriram,

the difference at T=0 between E_tot and F is due to the inclusion of the 
zero-point motion. I just studied bulk silicon some years ago and I found 
the same behavior for higher temperature (See Comp. Mat. Sci 22, 49 
(2001)). So it is not completely unexpected. But maybe you get some 
further hints here in the forum.

Best wishes,
Katalin


On Wed, 4 Apr 2007, Shriram Shivaraman wrote:

> Thanks a lot, Eyvaz. I found the fqha.f90 code on the forum and compiled it 
> with mpif77 to get the executable. I am not a physics major, so I don't 
> understand the code completely. 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?
>
> 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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