Tamm-Dancoff approximation

[zchen]

Hi, everyone:
In GPL version of Yambo Bethe-Sapeter equation can only be solved by Tammm-Dancoff approximation. My calculation of absorption for ce@C82 disagrees with the experiment. How can I solve BSE without TDA?
If I am only interested in the excitation from the bands near HOMO and final states are near LOMO what should I do?
Third question is how can I calculate the photoionization (electron goes to the continuum state) using Yambo?

Zhifan Chen
Dept of Physics
Clark Atlanta University
Atlanta GA 30314

[Daniele Varsano]

Dear Zchen,
the solution of the Bethe Salpeter equation beyond the Tamm-Dancoff approximation, unfortunately even if implemented
in Yambo, at the moment it is still not present in the GPL version. We hope to include it soon as GPL
in the next release of the code.

Regards,

Daniele

[andrea marini]

My calculation of absorption for ce@C82 disagrees with the experiment. How can I solve BSE without TDA?

Dear Zhifan Chen,

why do you think that the problem is related to the TDA ? What do you mean as disagreement ?

Third question is how can I calculate the photoionization (electron goes to the continuum state) using Yambo?

You cannot calculate directly photoemission (PE) as you do not know the shape of the outgoing electron wavefunction. With Yambo, however, you can calculate the peaks of the PE spectra and you can try to code yourself an expression for the intensities assuming some expression for the outgoing states (plane waves, for example). The Peaks of the PE are simply the quasiparticle energies.

[zchen]

Thanks. If I am only interested in the excitation from near HOMO states what should I do? This will save lots of computing time.

[andrea marini]

Thanks. If I am only interested in the excitation from near HOMO states what should I do? This will save lots of computing time.

What observable are you referring to ? Photemission, absorption ? And what are you exactly asking help for ? Please provide as more informations as possible so that we can try to help you.

[zchen]

I try to use Bethe-Sapeter equation to calculate the absorption of the Ce@C82. The calculation needs to include 177 occupied bands and some empty bands. Acturely I am only interested in the excitation between bands 175-177 to 178-180 etc.

Thanks

[andrea marini]

I try to use Bethe-Sapeter equation to calculate the absorption of the Ce@C82. The calculation needs to include 177 occupied bands and some empty bands. Acturely I am only interested in the excitation between bands 175-177 to 178-180 etc.

Dear zchen,

please edit your signature to include your complete affiliation and name so that it will appear in all your posts.

Regarding your question, can you post the input file of your calculation and any report file you already have so that we can understand what exactly you're running ? Without some more informations it is really difficult for us to give you any help.

From the report file we will se home electron, G-vectors, k-points you are using. The BSE hamiltonian size depends on many factors.