Dear Iyad
The main matter is that it is almost impossible or quite expensive to calculate
entire phonon dispersion for a very large system that has about 160 atoms. So
I would like to know whether it is possible to calculate Thermodynamic
properties by QHA avoiding such expensive step or do it only at the Gamma
point.
-------------------------------------------------Alex Granov??????????
??????-??????????? ???????? (MIPT)Moscow, Russia
Hi Alex,
Thermodynamical quantities depend strongly on low energy phonons ( mainly
the acoustic phonons, or the low energy part of the phonon density of
states; the Debye part). And to less extent on the high energy modes.
It also depends on how much precise you want to go in your calculations.
The more q-vectors you use in your calculations the better convergence of
quantities of interests.
I think the best thing to do is to sample for once the phonon density of
states using a fine mesh of q-vectors, and then to use it to calculate all
your quantities for all temperatures of interests.
Kindest Regards,
__________________________________
Iyad Al-Qasir, PhD
Assistant Professor
Department of Nuclear Engineering
University of Sharjah
Sharjah, UAE
On Sat, Dec 14, 2013 at 3:04 AM, Alex Granov <alex.granov at outlook.com>wrote:
> Hi
>
> As I understand from Phonon and QHA examples calculation of entire phonon
> dispersion is necessary to calculate and prepare fc file then
> Thermodynamic properties like Gibbs energy. I wonder if it is possible to
> avoid calculating entire phonon dispersion for a very large system say 160
> atoms to calculate its Gibbs energy or not. I appreciate any help in
> advance.
>
>
> -------------------------------------------------
> Alex Granov
> ?????????? ??????-??????????? ???????? (MIPT)
> Moscow, Russia
>
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