Orbital coupling in double-vacancy and two-electron systems

✍ Scribed by E.M.-L. Ohrendorf; F. Tarantelli; L.S. Cederbaum

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 738 KB
• Volume: 183
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(91)85089-f

✦ Synopsis

In double-core-hole states where two electrons are removed from different core orbitals, the SCF approach produces artiticially low singlet-state energies, leading to energy separations between corresponding singlet and triplet states which can be wrong by orders of magnitude. We present a theoretical analysis of this singlet-lriplelseparationproblem, revealing that the SCFbreakdown depends exclusively on the coupling between the core orbitals involved and can be viewed as a particular form of "spinconstrained" variational collapse in the singlet state. The SCF procedure on this state tries to mimic the energetically lower closcdshell singlet ground state even though it has to work with an open-shell configuration. We further prove analytically that it is still possible to obtain reliable estimates of the singlet-triplet splitting in a one-particle picture and show how to construct suitable orbitals. The theoretical analysis is complemented and supported by results on Six:+ (X = H, F) obtained by a propagator method, as well as a full treatment of the related two-electron system Si"+.