## triplets calculation in BSE

Various technical topics such as parallelism and efficiency, netCDF problems, the Yambo code structure itself, are posted here.

### triplets calculation in BSE

Hello all,

The BSE in the TDA is H = E + cV - W, where V and W are the bare Coulomb interactions and the statically screened Coulomb interactions, respectively. Therefore, in principle, we can calculate the singlets exciton energy by setting c = 2, and the triplets exciton energy by setting c = 0. In the manual of Yambo, I don't find how to set the parameter c. So, Yambo calculate the singlet exicton energy in default. Thereby, my question is can I calculate the triplet exciton energy by dropping V (V=0)? and which subroutines should I modified? Although it is interesting to find out the way by myself, asking question is the fastest way to get the answer.

Thanks you,
arlonne
arlonne
Department of Physics and Astronomy
Northwestern University, IL 60208
arlonne

Posts: 26
Joined: Thu Apr 18, 2013 4:50 pm

### Re: triplets calculation in BSE

Dear arlonne,
you can:
1) Perform a ground state calculation with spin and then run yambo. In this case the code will take care of the diagonalization in spin space and you should obtain both signlets and triplets poles.
2) set BSENGexx=1 (http://www.yambo-code.org/input_file/vars/var_BSENGexx.php) in the input file. Indeed this means to use only the g=0 vector for the V term, which is zero by definition as yambo is using the "overlined" V. In this case I'm not sure the oscillator strenghts are properly defined.

In any case pay attention that in the BSE approach the dielectric function is computed via the "overlined" polarization, thus you get the poles of this quantity. Check if this is what you need. (http://www.yambo-code.org/theory/docs/doc_BSS.php).

Best regards,
Davide
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
http://www.ism.cnr.it/en/davide-sangalli-cv/
http://www.max-centre.eu/

Davide Sangalli

Posts: 316
Joined: Tue May 29, 2012 4:49 pm
Location: Via Salaria Km 29.3, CP 10, 00016, Monterotondo Stazione, Italy

### Re: triplets calculation in BSE

Dear Davide,

Thanks,
arlonne
arlonne
Department of Physics and Astronomy
Northwestern University, IL 60208
arlonne

Posts: 26
Joined: Thu Apr 18, 2013 4:50 pm