NUMERICAL SINGULARITIES IN MANY-BODY MOMENTS EXPANSIONS

It is well known that connected moments expansions when used to approx imate the ground-state energy of Hamiltonian systems may suffer from e xtraneous singularities in various regions of parameter space. In this brief Letter a numerical investigation is presented to study an appro ximation scheme developed by Ullah to avoid the singularities found in moments expansions. Specifically, we study the single-impurity Wolff model as well as the 32-site Anderson lattice. (C) 1997 Elsevier Scien ce B.V.