Chapter 8 - Orbital Model of Electronic Motion in Atoms and Molecules

Abstract

What electrons are doing in molecules (at fixed positions of the nuclei) is described by their wave function – a solution to the Schrödinger equation. This equation however cannot be solved analytically. To obtain an approximate wave function the variational method is most useful. In this chapter a special kind of the variational method is presented, which restricts the form of the trial function to a single Slater determinant composed of molecular orbitals. In this way the variational method returns the best possible single Slater determinant. Each molecular orbital represents a kind of a single-electron wave function – a “home” for two electrons of opposite spin. We will now learn how to get the optimum molecular orbitals (Hartree–Fock method). Not only does this orbital picture give reasonable results, at the same time it also provides a kind of universal language of theoretical chemistry.