Complex-basis-function treatment of photoionization in the random-phase approximation

Complex-basis-function techniques are used to implement the equations of the random-phase approximation (RPA) in matrix form. This approach allows the direct extraction of total photoionization cross sections from a finite series of (complex) transition energies and oscillator strengths. The RPA is an effective means for including electron correlation effects on the photoionization of closed-shell atoms and molecules. The procedure demonstrated here provides a rigorous way of solving the RPA equations for continuum photoabsorption without resorting to numerical integration. The results of calculations on He and N2 are presented. Correlation effects are found to significantly influence the threshold behavior of the N2 photoionization cross sections.