Abstract
The traditional interpretation of Hund's rule due to exchange energy is not correct, which has already been verified for low-lying excited states of helium isoelectronic systems and light molecules. The stability of the highest spin multiplicity state is in fact ascribed to a decrease in the predominant electron-nucleus interaction energy of the system, which is realized at the cost of increasing the electron-electron interaction energy as well as the kinetic energy. The present article states that the same conclusion applies to the ground state of carbon, nitrogen, and oxygen atoms.
