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Dear admin,
I want to ask that when I do a BSE calculation for an AFM system, if I don't set the LTRIPLET = T, all the exciton states I got are singlet only ? Can I obtain the transitions between different spin channels?
Thanks a lot.

Dear user,

If you start from an antiferromagnetic ground state, and perform standard BSE calculations (LHARTREE=.TRUE.; LTRIPLET = .FALSE), you will obtain one set of singlet solutions and one set of triplet solutions. If you set LTRIPLET=.TRUE., which does the same as setting LHARTREE=.FALSE., you will obtain the remaining two sets of triplet solutions, with many (or maybe even all) transition probabilities being zero (i.e. these correspond to dark, potentially long lived triplet excitons).

In order to obtain non-zero transition probabilities for the triplets, you have to perform BSE calculations using LSORBIT = .TRUE. (of course you also need to perform the groundstate calculations using LSORBIT = .TRUE.).

Georg

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