number of plane wave used in response function

Deals with issues related to computation of optical spectra, in RPA (-o c) or by solving the Bethe-Salpeter equation (-o b). Includes local field effects, excitons, etc.

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Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

number of plane wave used in response function

Post by Weiqing Zhou » Wed Jul 03, 2019 3:44 am

Hi all,

I want to know the total number of plane-wave used in response function.
Q1 : Does FFTGvecs control this number ?

I use cutoff = 80 Ry in PWscf. If I don't specialize FFTGvecs and use its default value.
Q2 : what is the default value of FFTGvecs ? Does it mean that the same cutoff 80Ry is used in the calculations of response functions ?

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072

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Daniele Varsano
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Joined: Tue Mar 17, 2009 2:23 pm
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Re: number of plane wave used in response function

Post by Daniele Varsano » Wed Jul 03, 2019 9:27 am

Dear Weiqing,
the number of pw used in the response function is given by

Code: Select all

NGsBlkXd
for the dynamical screening or

Code: Select all

NGsBlkXs
for the static one.
You can assign the number in RL (reciprocal lattice vector) or as cutoff energy. If you give in RL then yambo chooses the closest number to fill a shell of G vector.

Code: Select all

FFTGvecs
controls the number of G-vectors or energy cut off for expanding the wavefunctions used in the FFT transforms.
The default value for FFTGvecs is given by the cutoff of the wavefunctions, so the one you used in the QE run (80Ry).

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

Re: number of plane wave used in response function

Post by Weiqing Zhou » Wed Jul 03, 2019 10:54 am

Dear Daniele,

Thanks!

For independent-particle RPA, NGsBlkXd =1 RL. Does it mean that there is only 1 pw used in the response function when local field effect is excluded. If not, how many pw used when NGsBlkXd =1 RL ?

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072

User avatar
Daniele Varsano
Posts: 2660
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

Re: number of plane wave used in response function

Post by Daniele Varsano » Wed Jul 03, 2019 10:57 am

Dear Weiqing,
if you exclude LF (independent particle) only the macroscopic component (G=0) of the response function is needed.

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

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