Oscillator strengths for the outer shells of the beryllium isoelectronic sequence are obtained using the relativistic random phase approximation in which the relativistic effects are included nonperturbatively. The results agree well with other accurate calculations that have been carried out for low-$Z$ elements. For high-$Z$ elements, our results should be very reliable. Both length and velocity formulas are used to calculate the oscillator strengths. The velocity formula is very sensitive to the weak inner-shell coupling, whereas the length formula is not. Inner-shell excitation energies and oscillator strengths are examined and compared with the helium isoelectronic sequence to show the effect of outer-shell screening.

• Received 19 October 1976

DOI:https://doi.org/10.1103/PhysRevA.15.1046