A simple demonstration of the origin of hund's rule for the helium 2S and 2P states

Abstract

Using hydrogenic atomic orbitals in the wavefunction 1s(1)2p(2), and simple “local” energy calculations E loc = ▪ ψ/ψ) the origin of Hund's rule of maximum spin multiplicity is examined for the 2 3P) and 2 1P) states of the helium atom. ln agreement with other recent studies, it is found that the greater electron-nuclear attraction stabilises the triplet state relative to the singlet state. Similar conclusions pertain for the (2 3S) and (2 1S) states when Slater 2s orbitals are used in the 1s(1)2s(2) wavefunctions. For each of the calculations, it is not necessary to take account of electron indistinguishability.