Unitary Transformations and Pair Energies. III. Relation to Perturbation Theory

Abstract

The effect of unitary transformations among the occupied orbitals of the beryllium atom is discussed. It is shown that pair‐pair interaction energies become large for choices other than the canonical Roothaan‐Hartree‐Fock orbitals. The many‐body perturbation theory diagrams responsible for these effects are discussed.