where r describes the distance to the center of mass. This changes the Dirichlet boundary condition, which requires the wave function to vanish at infinity (Ψ(∞) = 0), to the wave function vanishing at the location of the wall (Ψ(r C ) = 0). The corresponding wave function of the hydrogen atom and mono-and diatomic one-electron systems can be solved exactly, making them interesting model systems.