Yambo Community Forum

Dear all,
When calculating the exchange part of the self-energy, i.e., using `yambo -x`, do the input parameters `EXXRLvcs` and `VXCRLvcs` need to be kept equal? I noticed that the tutorial materials on the Yambo official website seem to offer different opinions.

On the webpage (https://enccs.github.io/max-coe-worksho ... onvergence), when inputting `yambo -gw0 p -g n -r -V par -F gw.in`, the webpage states: "`EXXRLvcs` controls the number of Reciprocal Lattice vectors (i.e., G-vectors) used to build the exchange self-energy, while `VXCRLvcs` does the same for the exchange-correlation potential reconstructed from DFT. Since these two quantities are to be subtracted, it is important to keep the same values here (and possibly not change the default maximum value)."

However, on the webpage (https://wiki.yambo-code.eu/wiki/index.p ... rtree_Fock), for the command `yambo -x -F hf.in`, the webpage describes different calculations by changing the value of `EXXRLvcs`, for example, to 10, 20, 30, and 40 Ry, without ensuring that the parameters `EXXRLvcs` and `VXCRLvcs` are equal.

So, in HF and GW calculations, is it necessary to keep the values of `EXXRLvcs` and `VXCRLvcs` equal? And is it generally necessary to modify the default maximum values of these two parameters?

Looking forward to your reply!

Sincerely,
Xiao

Dear Xiao,

in general, they do not need to be equal, as they control different quantities. What it is important is that they are both converged.
Considering that this part of the calculation is not the most cumbersome, unless it is needed by memory consideration, they can be kept fixed to their maximum, as this ensure convergence.

Best,
Daniele