NONUNIQUENESS IN THE CLOSE-COUPLING METHOD FOR E-HE SCATTERING

We present a general analysis of the close-coupling equations for e-He scattering. We shaw why the standard close-coupling expansion gives r ise to nonunique solutions and, by characterizing the manifold of nonu nique solutions, are able to construct equations with a unique solutio n. Our analysis concentrates on two models of target states; a frozen- core model in which one of the electrons is restricted to the 1s He+ o rbital, as has been used with great success recently, and also a model which uses full configuration-interaction target states. We develop m odified close-coupling equations by projecting out spurious solutions. A subtle difference between frozen-core and configuration-interaction models with respect to the manner in which antisymmetrization is inco rporated is noted. A calculation to illustrate the theory is presented .