about RPA-QP calculation

[yping]

Hi,
I want to ask whether we can use the GW 's quasiparticle energy to do the Random Phase Approximation calculation instead of using a scissor operator which simply opens rigidly the LDA gap as the self energy correction in yambo.
Thank you very much!
yuan ping
University of California, Davis

[andrea marini]

I want to ask whether we can use the GW 's quasiparticle energy to do the Random Phase Approximation calculation instead of using a scissor operator which simply opens rigidly the LDA gap as the self energy correction in yambo.

Dear Yuan Ping,

yambo can read the QP database created in a GW run to correct the energies in a subsequent RPA/BSE calculation. However, we switched off this option in the GPL release because of stability reasons. I am thinking to reintroduce it in one of the next revisions.

With the current revision you can, however, use the variables XfnQP_E to pass the code the parameters of the QP corrections.

Andrea

[hplan]

Dear Yuan Ping,

yambo can read the QP database created in a GW run to correct the energies in a subsequent RPA/BSE calculation. However, we switched off this option in the GPL release because of stability reasons. I am thinking to reintroduce it in one of the next revisions.

With the current revision you can, however, use the variables XfnQP_E to pass the code the parameters of the QP corrections.

Andrea

Dear Andrea,
A question about bands' scissor correction and stretching.
When we apply scissor correction, does it just move up all conduction bands for some value ? But what is the detail of bands' stretching ? I read the doc ,it doesnot give me much impression.

Regards
Hai-Ping

[myrta gruning]

Dear Hai-Ping,

regarding XfnQP_E has the form:

scissor | cond. stretching | val. stretching

The resulting correction to the energies:

Ev = val. stretching x Evo
Ec = cond. stretching x Eco + scissor

implies that the GW corrections depends (with good approximation) linearly on the energy so that GW not only opens the gap, but changes the form of (=stretches) the bands.
So If you have calculated the GW corrections for (several) bands/ and k-points of your sampling you can derive these values by fitting the GW energies Ev, Ec versus the input LDA energies Evo, Eco.
Quite often the linear fit describes quite well the QP energies (at least for the bands around the gap), with the values for both the stretching very close to 1.

I hope this answers your question
m

[hplan]

Dear Myrta,

Thanks for this detailed instruction.


Best Wishes,

Hai-Ping