[Pw_forum] Thermodynamic properties

[Iyad AL-QASIR]

I am a ware of what you are trying to do.  The maximum number of atoms I
dealt with was 64 atoms ( almost one third of your number) and I did it
using the supercell direct method. On the other hand Gamma point is not
enough.

Thank you

__________________________________
Iyad Al-Qasir, PhD
Assistant Professor

Department of Nuclear Engineering
University of Sharjah
Sharjah, UAE


On Sat, Dec 14, 2013 at 1:35 PM, Alex Granov <alex.granov at outlook.com>wrote:

>
> 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
> Московский 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 <http://pwscf.org/mailman/listinfo/pw_forum>>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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