## full GW+BSE calculation

Run-time issues concerning Yambo that are not covered in the above forums.

Moderators: andrea marini, Daniele Varsano, myrta gruning, Conor Hogan

Daniele Varsano
Posts: 2723
Joined: Tue Mar 17, 2009 2:23 pm
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### Re: full GW+BSE calculation

Dear Khaled,

1) When you solve the BSE, the meaningful part of the exciton energy is the real part. If you are interested in exciton lifetime you need to do a model for it first.
2) If you want to extract the transition dipole matrix you can write them either looking into ./src/bse/K_diag_compute_epsilon.F, when the epsilon is built after the diagonalization of the dielectric matrix.
Otherwise with the postprocessing ypp, when excitons are sorted out (have a look in ./ypp/exciton_sort_and_report.F), the BS_R are read, normalized and printed out.

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/

Khaled
Posts: 21
Joined: Fri Apr 10, 2015 10:11 am
Location: South Africa

### Re: full GW+BSE calculation

Dear Dr. Daniele Varsano,

Thanks a lot Dr. Daniele for your great help. I was able to extract the transition dipole matrix, but I am not sure a bout the units of the transition dipole matrix $| \sum_{vck} \langle vq-k | e^{-iqr} | ck \rangle A_{\lambda} |^{2}$
because I extracted this term alone (even I couldn't figure out if you used the electric dipole approimation for this term or not). Please, Can you help me for getting this information. Thank you in advance.

Best regards,

Khaled.
Khaled Shehata,
PhD Student,
School of Physics,
Witwatersrand University

Daniele Varsano
Posts: 2723
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

### Re: full GW+BSE calculation

Dear Khaled,
the internal unit in the code is the atomic unit (bohr for length, Hartree for energy etc..).
The electric dipole approximation it is used for the q=0 term.

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/

Flex
Posts: 37
Joined: Fri Mar 25, 2016 4:21 pm

### Re: full GW+BSE calculation

What is exactly the unit of the matrix elements ?

A transition dipole has SI units of Coulomb.meters, so here, should it be electron charge.bohr ?
Thierry Clette
Student at Université Libre de Bruxelles, Belgium

Daniele Varsano
Posts: 2723
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

### Re: full GW+BSE calculation

Dear Thierry,
yes, it should be as you wrote.

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/

haseebphysics1
Posts: 148
Joined: Sat Aug 17, 2019 2:48 pm

### Re: full GW+BSE calculation

Dear Yambors,

I have a pretty simple question.

In the BSE input file, one of the important parameter is BSSmod:

BSSmod= "d" # [BSS] (h)aydock/(d)iagonalization/(i)nversion/(t)ddft`

I was curious about the last option (t), here t represetns TDDFT? since it is just the method to solve BSE equation, so what does TDDFT means here. I have done TDDFT using LRCs approx. already.

Thanks,
MS - Physics,
LUMS - Pakistan

Daniele Varsano
Posts: 2723
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

### Re: full GW+BSE calculation

Dear Haseeb,
this variable was meant for a tddft kernel derived from the BSE equation: see e.g. Phys. Rev. Lett. 91, 256402 (2003). This feature is not present anymore in the code.
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/