Dear Martin,

Very quickly, next I will look again in details at your calculations.

1) For finite systems it is needed to insert the coupling part of the Hamiltonian (BSEmod=coupling) and uncomment #WehCpl, check the literature on that (eg

this paper), Tamm-Dancoff approximation most probably it is not valid.

2) In finite systems, being in plane waves, so periodic boundary conditions, you need to cut the coulomb potential in order to avoid

spurious interactions between repeated cells. Not doing that can have important biases, in particular in the GW gap (there is a lot of literature on that, for instance have a look

here). You can activate it in with yambo -r (I suggest you to use a sphere for this case).

3) You are using a real axis integration (very hard to converge!!) try also a Plasmon Pole approximations, even if not well justified, very often it gives the right answers and it is easier to converge than the real axis. Just to have a look on how much they differs, anyway have a look in the literature if you can have some information on the QP gap (both theoretical and experimental), just to individuate the poor calculation if GW or BSE (or may be both).

4) Convergences, check and recheck (eg BSENGBlk it looks me quite low with respect the total G vectors, but it is just an impression, not motivated).

5) BSE and CC are very different level of theory, so it is not guarantee they should give the same results, for instance if double excitation character excited states are present. Anyway I agree with you that the in this case you found a very big discrepancy.

Best,

Daniele