Extended Recursion in Operator Space (EROS), a new impurity solver for   the single impurity Anderson model
  We have developed a new efficient and accurate impurity solver for the single impurity Anderson model (SIAM), which is based on a non-perturbative recursion technique in a space of operators and involves expanding the self-energy as a continued fraction. The method has no special occupation number or temperature restrictions; the only approximation is the number of levels of the continued fraction retained in the expansion. We also show how this approach can be used as a new approach to Dynamical Mean Field Theory (DMTF) and illustrate this with the Hubbard model. The three lowest orders of recursion give the Hartree-Fock, Hubbard I, and Hubbard III approximations. A higher level of recursion is able to reproduce the expected 3-peak structure in the spectral function and Fermi liquid behavior. 
Jean-Pierre Julien and R. C. Albers