Quantum theory of many electron atoms and energy levels

This chapter is devoted to the discussion of many electron quantum systems. Most of the systems existing in nature comes under this category. Although the theory of many particle systems is complicated, this chapter presents the introductory description of such systems. In first part of this chapter, we present the general quantum mechanical description of such systems which is followed by various approximations needed to obtain some acceptable solution. Hartree and Hartree-Fock approach to compute the electron-electron interaction has been discussed. This is followed by the discussion of other small but important components of interactions such as spin–orbit interaction and relativistic effects. Towards the end, we have briefly mentioned the density functional-based Thomas-Fermi model of an atom which is the basis of density functional-based approaches for treating the many electron systems.