[Q-e-developers] Fast Fourier Transform

[Paolo Giannozzi]

On Mon, Nov 6, 2017 at 2:01 PM, Miguel Carvajal <
krvajal.miguelangel at gmail.com> wrote:

>
> CALL fwfft (‘Wave', rhoc(:,ii), dfftt)
>

fft grid (nr1s, nr2s, nr3s) in real space; in G-space, G-vectors for
Kohn-Sham orbitals, up to G^2 < Ecutwfc.
Suitable to compute \psi(r) from \psi(G), or vice versa


> CALL fwfft (’Smooth', rhoc(:,ii), dfftt)
>

fft grid (nr1s, nr2s, nr3s) in real space; in G-space, G-vectors for
Kohn-Sham orbitals squared, up to G^2 < 4*Ecutwfc.
Suitable to compute \rho(r)=\sum_i |\psi_i(r)|^2 and \rho(G)

CALL fwfft (‘Dense', rhoc(:,ii),dfftt)
>

fft grid (nr1, nr2, nr3) in real space; in G-space, G-vectors for charge
density and potentials, up to G^2 < Ecutrho.
Suitable to compute \rho(r) and \rho(G) in the presence of augmentation
charges, requiring a cutoff of Ecutrho >= 4*Ecutwfc

CALL fwfft ('Custom', rhoc(:,ii), dfftt)
>

fft grid (nr1t, nr2t, nr3t) in real space; in G-space, G-vectors quitable
for calculation of exact-exchange integrals, G^2 < Ecutfock.
Ecutwfc <= Ecutfock <= 4*Ecutwfc

when doing FFT on QE; as well as the appropriate grid to be used in each
> instance: *dfft, dfftp or  dffts*.
> I have some ideas but not a full understanding of it.
> Best regards,
>
> Lic. Miguel Carvajal - Instituto Balseiro - Bariloche
> National Atomic Energy Comission
> [+54] 2944782429 <+54%20294%20478-2429> (tel) / krvajal.miguel (skype)
> LinkedIn: in/krvajal <https://www.linkedin.com/in/krvajal/>
>
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>
>


-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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