Hi Andrea,

Thanks again for your answer. Let me answer and ask more.

How did you judge that differences between LDA and PBE are small ? Can you check the matrix elements of the xc potential, for example ?

I have not, in this specific case. I only know iron as example that LDA predicts a wrong crystalline structure, and in my work I have not found significant differences in band diagrams and other magnitudes when I have used both LDA and PBE. I have never evaluated numerical differences between wavefunnction. Of course, it is not consistent to mix the PBE wave functions with the LDA calculation.

Can you first do a pure LDA calculation and check that the effect of the commutator is small ?

Yes. this is the calculation for silicon. For PBE with nonlocal contributions the order of magnitude is terrible, although the shape is OK.

compara-ld-pbe.jpg

For CdTe, the LDA calculations are here. The NL calculation increases somewhat the values, the shape is not bad. With PBE the shape was absolutely wrong, as seen in a former post.

compara-cdte-lda.jpg

And, regarding doing GW on top of PBE if you are interested in doing it properly drop me an E-mail.

I think it is safer to swith to LDA. I have too many atoms to calculate and the complications with PBE are too much for me. In any case, I have to generate new pseudpotentials for Cd that include 4s and 4p in the valence, and the task for LDA and PBE is the same. For the moment I just want to proof that I can obtain the quasiparticle gap in the known case of CdTe.

Please, let me ask a few more questions about the GW calculations, even if its beyond the title of this post. I am following again the tutorial of Basic concepts of the GW approximation (

http://www.yambo-code.org/tutorials/GW/index.php). Three weeks ago in Lausanne I was primarily worried about compiling yambo with quantum espresso and I miss this part.

In the section of COHSEX, one reads that firsts it is needed the static screened interaction ( I guess, W(r,r',E=0 ) . For that one needs yambo -b and quasiparticle energies with yambo -b -g n. I am confused because it appears in a paragraph and later on, the COHSEX calculation is configured with yambo -g n -p c (without -b ). Then I have a few doubts

1) Does yambo -b -g n makes a SEX calculation, i.e., without the CO part?

2) Is it the same to perform

yambo -b;yambo;yambo -g n;yambo

as

yambo -b -g n;yambo

?

3) Do -b and -x act like adding ingredients to the calculations? If I do a COHSEX calculation without

calculating first the Hartree-Fock self-energy and the static screeing, what happens? Are them calculated on the fly ?

Note: I see that "yambo -p c -g n -F test-cohsex" and "yambo -x -b -p c -g n -F test-cohsex-x-b" produce the same input file but the order of some lines is different, I guess the order does not matter. Also,

"yambo -p p -g n -F test-ppa" and "yambo -x -b -p p -g n -F test-ppa-x-b" produce the same inputs.

but

"yambo -b -o b -y h" (from the CPC yambo article) produce a different input file than "yambo -o b -y h".

So, is there a general rule or a flexibility for BSE?

4) What is the interest in doing the COHSEX with empty bands? Is it to fix the parameter GbndRnge for later use in PPA or real axis calculation?

5) Hi Andrea,

Thanks again for your answer. Let me answer and ask more.

How did you judge that differences between LDA and PBE are small ? Can you check the matrix elements of the xc potential, for example ?

I have not, in this specific case. I only know iron as example that LDA predicts a wrong crystalline structure, and in my work I have not found significant differences in band diagrams and other magnitudes when I have used both LDA and PBE. I have never evaluated numerical differences between wavefunnction. Of course, it is not consistent to mix the PBE wave functions with the LDA calculation.

Can you first do a pure LDA calculation and check that the effect of the commutator is small ?

Yes. this is the calculation for silicon. For PBE with nonlocal contributions the order of magnitude is terrible, although the shape is OK.

compara-ld-pbe.jpg

For CdTe, the LDA calculations are here. The NL calculation increases somewhat the values, the shape is not bad. With PBE the shape was absolutely wrong, as seen in a former post.

compara-cdte-lda.jpg

And, regarding doing GW on top of PBE if you are interested in doing it properly drop me an E-mail.

I think it is safer to swith to LDA. I have too many atoms to calculate and the complications with PBE are too much for me. In any case, I have to generate new pseudpotentials for Cd that include 4s and 4p in the valence, and the task for LDA and PBE is the same. For the moment I just want to proof that I can to obtain the quasiparticle gap in the known case of CdTe.

Please, let me ask a few more questions about the GW calculations, even if its beyond the title of this post. I am following again the tutorial of Basic concepts of the GW approximation (

http://www.yambo-code.org/tutorials/GW/index.php). Three weeks ago in Lausanne I was primarily worried about compiling yambo with quantum espresso and I miss this part.

In the section of COHSEX, one reads that firsts it is needed the static screened interaction ( I guess, W(r,r',E=0 ) . For that one needs yambo -b and quasiparticle energies with yambo -b -g n. I am confused because it appears in a paragraph and later on, the COHSEX calculation is configured with yambo -g n -p c (without -b ). Then I have a few doubts

1) Does yambo -b -g n makes a SEX calculation, i.e., without the CO part?

2) Is it the same to perform

yambo -b;yambo;yambo -g n;yambo

as

yambo -b -g n;yambo

?

3) Do -b and -x act like adding ingredients to the calculations? If I do a COHSEX calculation without

calculating first the Hartree-Fock self-energy and the static screeing, what happens? Are them calculated on the fly ?

Note: I see that "yambo -p c -g n -F test-cohsex" and "yambo -x -b -p c -g n -F test-cohsex-x-b" produce the same input file but the order of some lines is different, I guess the order does not matter. Also,

"yambo -p p -g n -F test-ppa" and "yambo -x -b -p p -g n -F test-ppa-x-b" produce the same inputs.

but

"yambo -b -o b -y h" (from the CPC yambo article) produce a different input file than "yambo -o b -y h".

So, is there a general rule or a flexibility for BSE?

4) What is the interest in doing the COHSEX with empty bands? Is it to fix the parameter GbndRnge for later use in PPA or real axis calculation?

5) And turning back to the Im(eps) calculation. Can I obtain the GW dielectric function using the G0W0 energies, and not with the scissor operator and valence/conduction stretching via %XfnQP_E? How ?

Best regards

Eduardo

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