Triplet excitations in a non-spin polarized system

[javad]

Dear yambo users and developers

I'm studying a molecular crystal, by means of GW and BSE, that does not present any spin polarization.

However I would like to calculate the position of triplet excitations in this system,

How can I force yambo to perform spin-polarized calculations in this case?

with best regards
Javad

[Daniele Varsano]

Dear Javad,
triplet excitations can be calculated by doing a BSE calculation considering the direct term only in the kernel.
In practice:

Code: Select all

BSENGexx=0 RL

If you want you can also add the coupling part by setting:

Code: Select all

BSEmod="coupling"
WehCpl

Please note that while the triplet excitation energies are meaningful the oscillator strength (intensity) you get are meaningless.


Best,
Daniele

[javad]

Dear Daniele

thank you for the fast reply.

I have some another questions if you have time:
what about the dipole matrix elements? how one can get them right?
and do they have any meaning?
I mean the transitions between the ground state and the triplet states
are forbidden by the spin, so what is the meaning of the dipoles in this case,
also compared with phosphorescence experiments?

regards
Javad

[Daniele Varsano]

Dear Javad,

what about the dipole matrix elements? how one can get them right?
and do they have any meaning?
I mean the transitions between the ground state and the triplet states
are forbidden by the spin, so what is the meaning of the dipoles in this case,
also compared with phosphorescence experiments?

Correct, they are spin forbidden so I would say that they have not any sense. About phosphorescence I see here at least two difficulties:

1) Phosphorescence implies a transition form the minimum of the triplet energy surface and nobody guarantees it considering a vertical excitations.
2) It requires a spin-flip transition which is clearly not included in the present treatment.

Best,

Daniele