Master equation based steady-state cluster perturbation theory

A simple and efficient approximation scheme to study electronic transport characteristics of strongly correlated nano devices, molecular junctions or heterostructures out of equilibrium is provided by steady-state cluster perturbation theory. In this work, we improve the starting point of this perturbative, nonequilibrium Green's function based method. Specifically, we employ an improved unperturbed (so-called reference) state $\hat{\rho}^S$, constructed as the steady-state of a quantum master equation within the Born-Markov approximation. This resulting hybrid method inherits beneficial aspects of both, the quantum master equation as well as the nonequilibrium Green's function technique. We benchmark the new scheme on two experimentally relevant systems in the single-electron transistor regime: An electron-electron interaction based quantum diode and a triple quantum dot ring junction, which both feature negative differential conductance. The results of the new method improve significantly with respect to the plain quantum maste equation treatment at modest additional computational cost.