Saddle-point complex-rotation method for resonances

Abstract

A new procedure is suggested to improve the convergence of the complex-rotation method. Calculations are carried out for the $\mathrm{He}2s2s{}_{}{}^1{}_{}{}^{}S$ and $2s2p{}_{}{}^1{}_{}{}^{}P$ resonances. With a relatively small and simple wave function, one obtains a width which is stable to six digits over a wide range of rotational angles and nonlinear parameters. The results are compared with those of the most accurate theoretical calculations and experiments. The feasibility of applying this method to more complicated systems as well as multichannel problems is also discussed.