Tamm-Dancoff Approximation

[Daniele Varsano]

Dear Haseeb,
#WehCpl means eh-interaction for the coupling part, this it has no effect unless you activate the coupling.
The eh interaction in the resonant block is automatically included in the sex kernel.
From your report:

Code: Select all

#      |Exchange           [res]: yes
#      |Correlation        [res]: yes
#      |Kernel`s coupling       : no
#      |Exchange           [cpl]: no
#      |Correlation        [cpl]: no

eh interaction=correlation

Daniele

[haseebphysics1]

Dear Daniele,

From your kind answers and doing a little bit search over the internet, I have understood the following about BSEmod, kindly correct, if I am wrong!

BSEmod options:

Resonant: TDA (resonant only part)
Retarded: TDA, but anti-resonant also was taken into account, and this is the default for the BSEmod
Coupling: full BSE (coupling between resonant and anti-resonant), and off-diagonal elements of the BS matrix are taken into the account

Am I correct?

And the one-minute question is:
I know now how to activate the full BSE by going to the coupling in the BSEmod (exchange only) and using the WehCpl (for correlation also), but what is the difference between these two kinds of exchanges and couplings?

Exchange [res]: yes
Correlation [res]: yes

Exchange [cpl]: yes
Correlation [cpl]: yes

By the name I can recognize, this is for resonant and coupling parts, but can you please say something about their physical significance.

Thanks,

[Daniele Varsano]

Dear Haseeb,

resonant: ok
retarted: ok
Coupling:full BSE (coupling between resonant and anti-resonant). I do not know what you mean by off-diagonal element. Off diagonal are also present in the TDA. In the coupling you have also <cv|H|v'c'> elements besides the <cv|H|c'v'>.

but what is the difference between these two kinds of exchanges and couplings?

Exactly the same, the first are the terms for the kernel in the resonant block, the cpl terms in the coupling block.

The coupling terms are usually small and can be neglected (TDA).

About the physics, I invite you to look for textbooks, phD thesis etc.. and discuss with your colleagues and supervisors.

Best,
Daniele