CORRELATION-EFFECTS IN DOUBLY-EXCITED STATES OF POSITIVE-IONS

Doubly excited [core]n(1)n(2) states of many-electron positive ions ar e studied. The diagonalization of the interelectronic interaction oper ator is carried out within two different approaches. In the weak corre lation limit, perturbation theory is used whereas the two-electron dip ole approximation is applied in the strong correlation limit. Both app roaches result in the existence of a parameter permitting for lower [c ore]n(1)n(2) states the representation of the correlation energy and t he mixing coefficients of hydrogen-like configurations in a universal form. Using this parameter enables changes in correlation effects upon varying both the excitation of outer electrons and the core electron number to be traced. The regularities in the correlation energy of hig her [core]n(1)n(2) states are also investigated and it is shown that t he correlation energy is a non-monotonic function of the core electron number.