Lower bounds to bound state eigenvalues
BERTRAND G. GIRAUD · Physical Review C · 1978
Whenever the residual potential is repulsive the introduction of Pad\'e approximants into the BrillouinWigner perturbation expansion generates lower bounds to the exact eigenvalues. The method is extended to perturbation from a subspace and to singular repulsions.[NUCLEAR STRUCTURE Pad\'e approximants replace the Brillouin-Wigner (BW) equation by an equation whose solutions are lower bounds to the BW solutions.]