How to relate the number of G vectors with cutoff energies

[ljzhou86]

How to relate the number of G vectors for the exchange and for the correlation part of self-energy with cutoff energies?

I mean, the quantitative relationship between the numbers of G vectors and cutoff energies. In PRL 108, 226805 (2012) (Opto electronic Properties in Monol ayers of Hybridized Graphene and Hexagonal Boron Nitride), the author describe the caculation detail "35 and 5 Ry were used, respectively, for the exchange and correlation
part of the self-energy"; while in (Coupling of excitons and defect states in boron-nitride nanostructures,PHYSICAL REVIEW B 83, 144115 (2011)), the ref 43 state "40 000 G vectors for the exchange and 35 000 for the correlation part of the self-energy" in another way.

yambo -x, Exchnage: EXXRLvcs and NGsBlkXp define the number of exchange and correlation part, respectively. How to know, for example, the corresponding eutoff energies of 40000 and 35000 G vectors are ?

[Daniele Varsano]

Dear Zhou,
As in all plane wave codes, the relation is that the number of Gvec is such that |G^2/2|< E_cut.
If you give a number of Gvec then yambo ad Gvec to close shells. In the report you find the number of Gvecs for the first and last shells considering all the Gvec of the ground state. The number of Gvec given in energy will depend on the cell size. In the input file you can either give a number of Gvec in RL units or a cutoff in energy mHa.
Best,
Daniele