  We propose a fast impurity solver for the general quantum impurity model
based on the perturbation theory around the atomic limit, which can be used in
combination with the local density approximation (LDA) and the dynamical mean
field theory (DMFT). We benchmark the solver in the two band Hubbard model
within DMFT against quantum Monte Carlo (QMC) and numerical renormalization
group (NRG) results. We find that the solver works very well in the
paramagnetic Mott insulator phase. We also apply this impurity solver to the
DMFT study of the anti-ferromagnetic phase transition in the unfrustrated Bethe
lattice. The Neel temperature obtained by the fast impurity solver agrees very
well with the QMC results in the large Hubbard U limit. The method is a
promising tool to be used in combination with the LDA+DMFT to study Mott
insulators starting from first principles.
