Benchmark full configuration interaction and EOM-IP-CCSD results for prototypical charge transfer systems: Noncovalent ionized dimers

P. A. Pieniazek, S. A. Arnstein, S. E. Bradforth, A. I. Krylov, and C. D. Sherrill
J. Chem. Phys. 127, 164110 (2007)

Benchmark full configuration interaction (FCI) and equation-of-motion coupled-cluster model with single and double substitutions for ionized systems (EOM-IP-CCSD) results are presented for prototypical charge transfer species. EOM-IP-CCSD describes these doublet systems based on the closed-shell reference and thus avoids the doublet instability problem. The studied quantities are associated with the quality of the potential energy surface (PES) along the charge transfer (CT) coordinate and distribution of the charge between fragments. It is found that EOM-IP-CCSD is capable of describing accurately both the charge-localized and charge-delocalized systems, yielding accurate charge distributions and energies. This is in stark contrast with the methods based on the open-shell reference, which overlocalize the charge and produce a PES cusp when the fragments are indistinguishable.

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