Level-level photoionization cross section discussion

Based on the HFR method and considering configuration interaction between bound states, some problems and inadequacies what may be occurred in the calculation of photoionization cross sections by using Cowan's theory are discussed, and correct method is given to solve these problems. Using the method, photoionization cross sections of Li, Na and Cs atoms are calculated and compared with references. The difference and relationship between the orbital-orbital and the summed level-level photoionization cross sections are discussed and analysed theoretically