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

[Atsushi T. <atz...@gm...>]

Hi,

No. VASP can not calculate third-order force constants by DFPT.

Togo

On Thu, Oct 17, 2019 at 9:04 PM Bohdan Andriyevskyy
<boh...@tu...> wrote:
>
> Hello,
>
> in view of the below discussion I would like to know whether one can use
> the results (files) of the force constants obtained using VASP-DFPT for
> the next calculations of the thermal conductivity coefficients using
> phono3py. If yes, I would be thankful for yours replies and instructions.
>
> Bohdan
>
> W dniu 17.10.2019 o 08:25, Martin Bäker pisze:
> > 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
> >
>
>
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-- 
Atsushi Togo
Elements Strategy Initiative for Structural Materials, Kyoto university
E-mail: atz...@gm...