Electron-electron correlation in highly charged atoms

The relativistic random-phase approximation (RRPA) is introduced to account for electron-electron correlation in atoms and ions of high nuclear charge where non-relativistic many-body methods are inadequate. To provide a basis for this study of the RRPA, the Dirac-Fock (DF) theory is reviewed. Applications of the DF equations to determine inner-electron binding energies in heavy atoms are given illustrating the influence of relativistic effects in situations where correlations are unimportant. The RRPA equations are derived as natural generalizations of the DF equations. Examples of RRPA calculations of discrete excitations and of photoionization are given illustrating situations where both relativistic and correlation effects play important roles