In chemistry, we have two kinds of fundamental particles: electrons and nuclei. These have very different mass scales yet similar charge, therefore in this paradigm we may invoke the Born-Oppenheimer approximation, to separate nuclear and electronic degrees of freedom. This is not always an excellent approximation in all circumstances, but is often a suitable starting point in understanding the more general-setting. Because electrons must be treated quantum mechanically, the Schrödinger equation is required. Beyond hydrogenic atoms, molecules have multiple electrons, and hence the Many-Body Schrödinger-equation (MBSE) is the fundamental equation describing their distribution. Then this problem transposes into solving the nuclei-clamped static Schrödinger equation for the electrons. It is this problem we wish to understand at a basic level.