Why the 4s Orbital Is Occupied before the 3d (the authors reply)

Abstract

We are glad that Bills has calculated (ε_d'–ε_s) for the two cases, Cr and Cu, for which we did not have the optimized orbitals of the 4s^23d^n configuration. It now seems that the (ε_d'–ε_s) is positive throughout the series when determined from 4s^23d^n wavefunctions. In one respect the new results make our conclusion wider. Since (ε_d"–ε_s') is also positive for the 4s^13d^(n+1) configurations, it can now be said that the substitution 4s → 3d gives a less stable configuration in every case, and not just when the original configuration was the one suggested by the spectroscopic ground state.