Strong Coupling Solver for the Quantum Impurity Model

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.Comment: 5 pages, 5 figures. to be published in Physical Review

Phase diagram, energy scales and nonlocal correlations in the Anderson lattice model

We study the Anderson lattice model with one f-orbital per lattice site as the simplest model which describes generic features of heavy fermion materials. The resistivity and magnetic susceptibility results obtained within dynamical mean field theory (DMFT) for a nearly half-filled conduction band show the existence of a single energy scale $T^*$ which is similar to the single ion Kondo temperature $T_K^o$. To determine the importance of inter-site correlations, we have also solved the model within cellular DMFT (CDMFT) with two sites in a unit cell. The antiferromagnetic region on the phase diagram is much narrower than in the single-site solution, having a smaller critical hybridization $V_c$ and N\'eel temperature $T_N$. At temperatures above $T_N$ the nonlocal correlations are small, and the DMFT paramagnetic solution is in this case practically exact, which justifies the ab initio LDA+DMFT approach in theoretical studies of heavy fermions. Strong inter-site correlations in the CDMFT solution for $T<T_N$, however, indicate that they have to be properly treated in order to unravel the physical properties near the quantum critical point.Comment: 10 page