Re: [Phonopy-users] Calculating force sets to get force constants vs calculating force constants directly using DFPT

[Martin B. <mar...@tu...>]

Yes, there wil be some (usually minor) differences - the vasp DFPT uses
perturbation theory whereas the displacement POSCARs use actual finite
displacements. You may also notice that the number of generated
displacements might differ between the two methods.

I have some limited experience with this and found that the results
differ by a few percent.

Hope this helps,
Martin.

On Tue, 15 Oct 2019 17:08:04 +0000
"Appleton, Robert J" <ra...@ca...> wrote:

> Hello,
> 
> I am curious about the similarities and differences of the methods one can use VASP along with phonopy to calculate the force constants. It seems you can either calculate the force sets by doing vasp calculations on each of the displacement poscars and then use the force sets to write a file containing the force constants, or you can calculate the force constants directly using vasp-DFPT on the supercell. I saw that for the Si example there is no difference in the phonon dispersion or density of states using either of these methods. Are they the same or is there slight differences?
> 
> Thanks,
> 
> Robert Appleton


-- 
                   Priv.-Doz. Dr. Martin Bäker
                   Institut für Werkstoffe
                   Technische Universität Braunschweig
                   Langer Kamp 8
                   38106 Braunschweig
                   Germany
                   Tel.: 00-49-531-391-3065  
                   Fax   00-49-531-391-3058
                   e-mail <mar...@tu...> 
		   http://www.tu-braunschweig.de/ifw/institut/mitarbeiter/baeker
              	   http://www.scienceblogs.de/hier-wohnen-drachen
		   Twitter: @Drachenblog