COMPARISON OF THE SADDLE-POINT METHOD AND THE FESHBACH-TYPE PROJECTION METHOD

In this work, we compare the saddle-point method with the Feshbach-type projection-operator method using experimental and theoretical data in the literature. It appears that the saddle-point energy gives a better approximation to the resonance energy. This result is explained in terms of the variational principle of quantum mechanics. It is also pointed out that the existing Feshbach-type projection method is not suitable for general triply excited states such as (2snlnl) where n,n3. © 1990 The American Physical Society.