Chapter 16 - Post-Hartree–Fock methods

Abstract

In this chapter we discuss the post–Hartree–Fock methods and how electron correlation can be introduced into the many-electron wavefunctions. After a section on the evaluation of the matrix elements between general Slater determinants in terms of density matrices, we discuss, first, the physical interpretation of the electron correlation problem in terms of spinless pair densities, outlining in detail the difference existing between molecular orbital and Heitler–London approximations for H2, and, next, how the correlation problem can be managed in terms of different interconfigurational (configurational interaction) methods. Then, we present in some detail the generalized valence bond method, the Kołos–Wolniewicz method, and the multiconfigurational self-consistent-field method, and introduce two advanced theoretical methods for dealing with electron correlation, second quantization and diagrammatic techniques, up to consideration of the coupled-cluster R12 many-body perturbation theory method. Lastly, the density functional theory is discussed as a method which directly includes from the beginning electron correlation in semiempirical calculations.