The influence of electron correlation on generalized oscillator strengths for He

The excitation transitions considered are 1 1 S to 2 1 P and 1 1 S to 3 1 P. Electron correlation is introduced into the description of the 1 1 S ground state in a systematic way by using the natural expansion of a configuration-interaction (CI) wavefunction developed by Weiss. By truncating this expansion to the first X terms and renormalizing a series of wavefunctions ranging from a Hartree-Fock equivalent (X=1) to the full CI function (X=15) are obtained. Operating within the first Born approximation, three standard formulations for evaluating f(K) are used and their sensitivity with respect to correlation effects is discussed and a comparison of the present results is made with those of other workers. Although the inclusion of the first correlation configuration in the 1 1 S wavefunction did not necessarily guarantee an improvement in f(K), the introduction of the second correlation term in the natural expansion gave rise to a significant improvement in f(K) for all K regardless of the mode of calculation.