Triplet excitations in a non-spin polarized system

Questions and doubts about the spin-dependent version of Yambo.

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Triplet excitations in a non-spin polarized system

Postby javad » Fri Jun 05, 2015 8:34 am

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
Javad Exirifard
IPM - Institute for Research in Fundamental Sciences
P. O. Box 19395-5746
Niavaran Square
Tehran, Iran
javad
 
Posts: 30
Joined: Fri Feb 28, 2014 10:23 pm

Re: Triplet excitations in a non-spin polarized system

Postby Daniele Varsano » Fri Jun 05, 2015 8:45 am

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
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/
User avatar
Daniele Varsano
 
Posts: 1950
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Re: Triplet excitations in a non-spin polarized system

Postby javad » Mon Jun 08, 2015 9:46 am

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
Javad Exirifard
IPM - Institute for Research in Fundamental Sciences
P. O. Box 19395-5746
Niavaran Square
Tehran, Iran
javad
 
Posts: 30
Joined: Fri Feb 28, 2014 10:23 pm

Re: Triplet excitations in a non-spin polarized system

Postby Daniele Varsano » Mon Jun 08, 2015 3:32 pm

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
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/
User avatar
Daniele Varsano
 
Posts: 1950
Joined: Tue Mar 17, 2009 2:23 pm


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