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Dear all,
I have a question that when I do a BSE calculation including the SOC effect, if I want to get the spin-triplet exciton, should I uncomment the "LTRIPLET = T" tag?
I check my results and it seems that when I consider the soc in a non-polarized system, the lowest exciton is spin-triplet directly.
But I'm not so sure
Thank you so much !

Best,
Yuanchang Li

Dear Yuanchang Li,

If you include spin-orbit coupling in your BSE calculation, you should not set LTRIPLET = .TRUE. as, in principle, there is no more distinction between spin channels and the singlet and triplet configurations are mixed. You get the full set of solutions by running the calculation with LHARTREE = .TRUE. and LTRIPLET = .FALSE..

I check my results and it seems that when I consider the soc in a non-polarized system, the lowest exciton is spin-triplet directly.

The lowest exciton should be a triplet state as the repulsive exchange interaction in singlet configurations reduces the binding energy of excitons compared to the triplet states.