Correlation Energy Contributions from Low-lying States to Density Functionals in the KLI Approximation

Abstract

In this paper we consider a criterion to allow a new coupling between density functional theory and configuration interaction methods. We study as a possible criterion the ordering of the orbital energies produced by the exchange-only KLI potential. This idea arises from the observation that the KLI potential behaves as - 1/r for large r in agreement with the known properties of the exact Kohn-Sham potential. The KLI bound states can thus be classified into valence and Rydberg orbitals, the latter not expected to make an important contribution to the correlation energy. We verify this assumption for the first terms of the He and Be series, as in the former only dynamical correlation is supposed to be present, whereas in the latter peculiar near-degeneracy effects intervene. In addition, exact results are given for the Be series in the limit of infinite nuclear charge. Although the contribution to the correlation energy from the low lying virtual states are significantly different for the two series (saturating as Z increases for the He series and being proportional to Z for large Z for the Be series) the remaining contributions to the correlation energy for both series saturate suggesting the application of DFT to the calculation of this latter contribution.KeywordsCorrelation EnergyOrbital EnergyConfiguration InteractionVirtual StateSlater DeterminantThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.