[Pw_forum] Thermodynamic properties

Alex Granov alex.granov at outlook.com
Sat Dec 14 10:35:36 CET 2013

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 GranovМосковский физико-технический институт (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
> Московский физико-технический институт (MIPT)
> Moscow, Russia

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