Yambo Community Forum

Dear Luca,
once the supercell volume and RC are choose in a proper way, ie that all the interaction in your molecule is taken into account and interaction with periodic cell is truncated, than the qp energy value should not change anymore. When setting Rc you should consider some space for the spill out of the charge. You can see inset it in the inset of Fig.6 of the paper you mentioned. So you can fix Rc such that Rc > system_size+spillo out (some au), next your cell should be large enough that system-system distance is larger than Rc. You can try to consider an even bigger volume to check that the QP energies does not vary too much.
Yes, as you say, when increasing the supercell size the parameter should be consistent, both G vectors and bands included. G-vectors are automatically accounted if you fix a cutoff in energy instead that in number of reciprocal lattice vectors.

Unfortunately i see no where in the paper explicitly which one is more important, i assume QP convergence with respect to super-cell volume is much more important, but i would like to be sure of this fact.

In the same paper you can see that volume effects in the binding energies passing from the smallest volume to the larger, varies of about 0.5eV (FIg.7), and with the bigger volume it is more or less converged, while in the QP gap the variation is ~2eV.

Best,
Daniele