While doing the analysis of mono layer h-BN we found that it is an indirect band gap semiconductor
Well, may be you need to check your ground state, here a paper you may have a look for reference (Fig.4) but surely you can find 2D-HBN in literature to compare with:
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Also, Is Bethe Salpeter analysis able to capture indirect transitions? If not then how can we calculate transition probability for indirect transition?
Yes, in line of principle it is possible, but the q-finite BSE although implemented in Yambo it has not been yet released in the GPL version, we plan to make it public soon.
Can you help me to find out the position of k point 19 and 16 in my band structure?
In any report file, including the setup, you can find the K vector corresponding to each K index, e.g.
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*X* K  : 0.000000 -0.769211 0.000000 ( cc) * Comp.s 2736 * weight 0.08333
0.000000 -0.500000 0.000000 (rlu)
Index 4 that correspond to the wave vector report in cartesian coordinate (cc) and reciprocal lattice unit (rlu).
And at k point 16 it is showing transition from band 8 to band 4. What does this means?
In the BSE you have both the resonant part, transition v-> c and anti resonant c -> v. In the resonant approximation (Tamm Dancoff) the two blocks are decoupled, when introducing coupling the two are mixed.
Are you adding the coupling term in your BSE?
Can you please help me to extract the transition matrix elements from this?
The transition matrix elements are calculated here:
you can follow this thread
on how to write them. Please note that if you have the ./SAVE/ndb.dipoles these are not re-calculated.
Other option is here:
and write on a txt fie BSS_dipoles
in the loop around line 75 they are assigned, at the beginning of the loop you have the corresponding index of valence, conduction bands and k point, but here I'm afraid that the BZ
referes to the entire BZ and not the irreducible.
Last option (may the easiest) is to use yambo-py to extract them from the database:
Hope it helps,