Electrons are the “glue” that holds the nuclei together in the chemical bonds of molecules and ions. Of course, it is the nuclei’s positive charges that bind the electrons to the nuclei. The competitions among Coulomb repulsions and attractions as well as the existence of non-zero electronic and nuclear kinetic energies make the treatment of the full electronic-nuclear Schrödinger equation an extremely difficult problem. Electronic
In this Chapter, many of the basic concepts and tools of theoretical chemistry are discussed only at an introductory level and without providing much of the background needed to fully comprehend them. Most of these topics are covered again in considerably more detail in Chapters 6-8, which focus on the three primary sub-disciplines of the field. The purpose of the present Chapter is to give you an overview of the field that you will learn the details of in these later Chapters
When one is faced with a condensed-phase system, usually containing many molecules, that is at or near thermal equilibrium, it is not necessary or even wise to try to describe it in terms of quantum wave functions or even classical trajectories of all of the constituent molecules. Instead, the powerful tools of statistical mechanics
