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 > ?????????? ??????-??????????? ???????? (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 > *>* ?????????? ??????-??????????? ???????? (MIPT) > *>* Moscow, Russia > *> > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20131214/0d6ce303/attachment.html
