Fast impurity solver based on Gutzwiller variational approach

A fast impurity solver for the dynamical mean-field theory (DMFT) named two-mode approximation is proposed based on the Gutzwiller variational approach, which captures the main features of both the coherent and incoherent motion of the electrons. The solver works with real frequency at zero temperature and it provides directly the spectral function of the electrons. It can be easily generalized to multiorbital impurity problems with general on-site interactions, which makes it very useful in local-density approximation plus DMFT. Benchmarks on one- and two-band Hubbard models are presented, and the results agree well with those of exact diagonalization. Lastly a few cartoonlike five-band results are presented, showing that the present solver is really capable of dealing with multiband systems.