Good day,

I have a question about how best to obtain the retarded Green’s function for a lead in Kwant.

Kwant already has a way of calculating the retarded self-energy of a lead (the ‘selfenergy’ method of ‘StabilizedModes’ [1]), however there is no equivalent routine for the retarded Green’s function. As far as I am aware one may obtain the self-energy from the Green’s function by sandwiching it between a V (inter-cell hopping) and a V^\dagger, and I was wondering if there is a reason why there is not a routine that returns the Green’s function directly.

One possibility is because the modes, as calculated by Kwant, are (in general) in a weird basis related to the singular value decomposition of V, and only a part of the SVD is stored with the stabilized modes, which makes it impossible to “get out” the modes in the tight-binding basis as required for the Green’s function.

Is my understanding correct, or am I missing something?

Thanks,

Joe

[1]: https://gitlab.kwant-project.org/kwant/kwant/-/blob/master/kwant/physics/leads.py#L185