Hi,
Now I am stuck with the vlead_interface part. According to the documentation it is a sequence of Site instances, which as much I understand would be a list of the position and SiteFamily, but I don't know how to define them.
`Site` objects are returned by lattice objects in Kwant. whenever you do: lat = kwant.lattice.square() site = lat(0, 1) then `site` is an instance of a `Site` with `lat` as its family and a tag of `(0, 1)`. You need to provide the interface sites so that Kwant knows how you have ordered the degrees of freedom in your self energy matrix. Given that you are creating a virtual lead and want to get the Green's function everywhere in the system, you could do something like: syst = kwant.Builder() ... # build the system greens_function_sites = syst.sites() mount_vlead(syst, greens_function_sites, 1) fsyst = syst.finalized() The only caveat is that when you obtain the Green's function at the interface with the virtual lead (i.e. on all the sites) the degrees of freedom will be ordered like the `greens_function_sites` sequence, and *not* in the same way as `fsyst.sites`. Hope that helps, Joe