Hi Rudolf,
> The kwant documentation on kwant.solvers.common.GreensFunction() states > that calling this method will return the retarded Green's function. Does > this method evaluate the equilibrium or non-equilibrium retarded Green's > function? I am interested in the time-dependent non-equilibrium density > matrix, which can be written as the kinetic lesser NE Green's function > G_<(t,t') > > rho_neq (t) = -iG_<(t,t')|t=t'. 'kwant.greens_function' essentially gives you a few matrix elements of the following quantity: Gᴿ(E) = (H + Σ(E))⁻¹ where Σ is the self-energy of the leads at energy E. Specifically it gives you the matrix elements that connect the interface sites of the different leads; these are the matrix elements needed to calculate transport quantities (like conductance). In order to calculate the lesser Green's function for the time-independent, nonequilibrium case (i.e. different chemical potentials / temperatures in different leads) you would need to take a different approach I think. One way to do so would be to apply eq. 22 of https://arxiv.org/abs/1307.6419 to the special case where Ψ_αE(t) has trivial time dependence: Ψ_αE(t) = exp(-iEt) Ψ_αE where Ψ_αE is the scattering state corresponding to incoming mode α at energy E (i.e. what kwant.wave_function gives you). If your system is *time-dependent* then you will need to calculate the time-evolved scattering states, which Kwant cannot give you directly. Indeed I did some work on calculating such quantities during my PhD., and one of the outputs was a code "tkwant", which is essentially a solver for working with Kwant systems that include time-dependence. It essentially does the time evolution and energy integration for you. tkwant is still actively developed, but I am no longer directly involved; you can check it out here: https://gitlab.kwant-project.org/kwant/tkwant/ there's also links to the documentation which includes some examples which should help you get started if this is the direction you want to go. Happy (t)kwanting, Joe
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