FLEX-description of the spectral functions near singlet-triplet transition

In a previous article, we have investigated the non-equilibrium two-level Anderson model with a simple iterative perturbation theory. Here we use here a more sophisticated perturbative method, the fluctuation-exchange (FLEX) approximation. The great advantage of FLEX is its $\mathit{\text{conserving}}$ nature, and that it can describe well the Kondo energy scale, the Kondo-temperature, $T_K$. As it was expected from the results obtained with iterative perturbation theory, the FLEX description can give back also the relevant features of the spectral properties.