ELIMINATION OF HYPERSPHERICAL GHOST STATES CAUSED BY A CLOSED-SHELL CORE - TEST WITH THE RESTRICTED TEMKIN-POET MODEL

Ghost states arise in applications of the hyperspherical close-couplin g method to atoms with two valence electrons outside a closed-shell co re. A rigorous formulation of ghost-state elimination is proposed on t he basis of a projection operator. Its practical implementation exploi ts the R-matrix propagator. The procedure is tested for the Temkin-Poe t s(2) model by removing a target orbital regarded as an occupied core state. The partial success of the recently proposed scheme of Zhou an d Lin [Phys. Rev. A 51, 1286 (1995)] is accounted for as due to an ext reme insensitivity of the R-matrix states on the projection parameter.