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### number of plane wave used in response function

Posted: **Wed Jul 03, 2019 3:44 am**

by **Weiqing Zhou**

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

### Re: number of plane wave used in response function

Posted: **Wed Jul 03, 2019 9:27 am**

by **Daniele Varsano**

Dear Weiqing,

the number of pw used in the response function is given by

for the dynamical screening or

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.

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

### Re: number of plane wave used in response function

Posted: **Wed Jul 03, 2019 10:54 am**

by **Weiqing Zhou**

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

### Re: number of plane wave used in response function

Posted: **Wed Jul 03, 2019 10:57 am**

by **Daniele Varsano**

Dear Weiqing,

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

Best,

Daniele