Dear Sitangshu,

the first variable

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`DbGdQsize`

is active when you compute the response function using

the double-grid technique either in G-space or with the inversion solver in BSE:

http://www.yambo-code.org/input_file/ypp/ypp_rim.phpIn the past the technique was called "RIM" since the second grid was meant to be a random grid.

We renamed it "Double Grid" since the second grid in principle can be anything.

You can ignore it if you are not using a double grid.

The value of "DbGdQsize" goes from 0 to 1, where 1 corresponds to the most accurate calculation, i.e. yambo fully uses the double grid.

Lowering its value only a part of the double grid is used.

The second variable

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`BSSPertWidth`

refers to the perturbative approach to BSE when quasi-particles lifetimes are used.

The equations are the same as the ones for perturbative SOC used in the supplementary of this PRL:

https://journals.aps.org/prl/abstract/1 ... 111.216805However now the perturbation is not the SOC.

Thus, if a BSE calculations loading the QP lifetimes is performed (as in this PRL:

https://journals.aps.org/prl/abstract/1 ... 101.106405), yambo can

(a) solve the BSE for the non hermitian hamiltonian

(b) solve the hermitian problem without the QP lifetimes and then add a width to each pole with a perturbative approach

Case (a) is the default, case (b) is activated by the flag BSSPertWidth