*Article* **Photoionization of Atomic Systems Using the Random-Phase Approximation Including Relativistic Interactions**

**Pranawa C. Deshmukh 1,2 and Steven T. Manson 3,\***


**Abstract:** Approximation methods are unavoidable in solving a many-electron problem. One of the most successful approximations is the random-phase approximation (RPA). Miron Amusia showed that it can be used successfully to describe atomic photoionization processes of many-electron atomic systems. In this article, the historical reasons behind the term "random-phase approximation" are revisited. A brief introduction to the relativistic RPA (RRPA) developed by Walter Johnson and colleagues is provided and some of its illustrative applications are presented.

**Keywords:** photoionization; random-phase approximation; relativistic-random-phase approximation
