The Numerical Renormalization Group (2016)

The first one shows the spectral function where you can notice the broadening of the quantum dot energy levels because of interaction with the leads and also the Kondo resonance, the next one shows the renormalization group flow for the same model. I don’t know much about the later, but by looking at the code I can tell that both are capable of using symmetries to speed up the calculations and improve accuracy, they work for non-flat density of states, NRG can be used together with Dynamical mean-field theory, they allow multiple channels, the spectral function can be calculated much better with DM-NRG (at finite temperature, too), they implement z-averaging, they can calculate out from the spectral function the Green function (with Hilbert transform) and more. Very shortly, the spectral function for the d operator in the T=0 limit is:

There is enough information about how to derive it and implement it in the links, the code is in the class.

Source: compphys.go.ro