Pathologic inversion of core orbitals in approximate Hartreendash;Fock calculations

摘要

The common sense in quantum chemistry that each bonding orbital is filled before the corresponding antibonding orbital is shown to be often violated for the core orbitals of diatomic systems in approximate Hartreendash;Fock calculations. Through theoretical analysis of the core orbital energies and numerical analysis of some specific diatomic systems, the origin of this pathologic ordering is suggested to be unusual mixing of valence orbitals into core orbitals induced by the use of basis sets with unbalanced corendash;valence quality.