Simplified Parquet Equations for the Anderson Impurity Model: Comparison with Numerically Exact Solutions

We use an analytic solver for the single-impurity Anderson model based on simplified parquet equations to describe the Kondo asymptotics. This scheme uses a two-particle self-consistency to control the strong-coupling Kondo critical behavior of this model at half filling. The equations can be written in the real-frequency representation, which gives us direct access to spectral functions unlike numerical schemes in the Matsubara formalism. We compare our results to those obtained by second-order perturbation theory, numerical renormalization group, and continuous-time quantum Monte Carlo in order to assess the reliability of this approximation.