Basic Approximations in the Theory of the Chemical Bond

Abstract

The modern theory of the chemical bond is based on the quantum mechanics of systems composed of electrons and atomic nuclei, assuming that solution of the fundamental quantum mechanical equation leads to a complete description of the system. As follows from the two preceding chapters, difficulties lie not in the formulation of the Schrödinger equation, but in its solution. As even three-particle systems are not exactly solvable, problems interesting for chemists must be simplified by conversion into model systems. The mere fact that, as a rule, an isolated system is treated (an atom, a molecule, a solid or a system of several partial subsystems) is a kind of abstraction, as the influence of the surrounding medium, for example the influence of a solvent, is frequently ignored.