  Although several impurity solvers in the dynamical mean field theory (DMFT)
have been proposed, especially in multi-band systems, there are practical
difficulties arising from a trade-off between numerical costs and reliability.
In this study, we re-interpret the iterative perturbation theory (IPT) as an
approximation which captures the strong correlation effects by mimicking the
particular frequency structures of the exact full vertex, and extend it such
that it can have efficiency and reliability simultaneously by modifying IPT
vertex using the parquet equations. We apply this method to several models to
evaluate their validity. We confirm that our method shows good agreements with
the numerically exact continuous-time quantum Monte Carlo method in the
single-site DMFT calculation.
