Approximations to the ground-state energy of the single-impurity Kondo model using variational and connected-moments expansions

Abstract

We have studied the ground-state energy of the single-impurity Kondo model. Results using a strict 4\ifmmode\times\else\texttimes\fi{}4 Lanczos truncation are shown to be equivalent to a relaxed 26\ifmmode\times\else\texttimes\fi{}26 Lanczos basis. An application of the connected-moments expansion to obtain the ground-state energy of this model many-body Hamiltonian is shown to be limited to certain regions of parameter space.