Abstract
It is found that a general description of excitations in terms of self-energy effects such as relaxation, correlation, and electron-hole interactions, is possible. A formalism is developed to analyze the contributions to each of these effects, and criteria are established which, if met, allow a much simpler description of the excitation processes than with the general formalism. These procedures are tested by calculations on atomic Be and Ne, and the structure of each of the processes contributing is studied.