Benchmark full configuration interaction and equation-of-motion coupled-cluster model with single and double substitutions for ionized systems results for prototypical charge transfer systems: Noncovalent ionized dimers

Pieniazek, Piotr A.; Arnstein, Stephen A.; Bradforth, Stephen E.; Krylov, Anna I.; Sherrill, C. David

doi:doi:10.1063/1.2795709

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Accurate extrapolation of electron correlation energies from small basis sets

A new two-point scheme is proposed for the extrapolation of electron correlation energies obtained with small basis sets. Using the series of correlation-consistent polarized valence basis sets, cc-pVXZ, the basis set truncation error is expressed as δEX∝(X+ξi)−γ. The angular momentum offset ξi captures differences in effective rates of convergence previously observed for first-row molecules. It is based on simple electron counts and tends to values close to 0 for hydrogen-rich compounds and va...

Troubleshooting time-dependent density-functional theory for photochemical applications: Oxirane

The development of analytic-gradient methodology for excited states within conventional time-dependent density-functional theory (TDDFT) would seem to offer a relatively inexpensive alternative to better established quantum-chemical approaches for the modeling of photochemical reactions. However, even though TDDFT is formally exact, practical calculations involve the use of approximate functional, in particular the TDDFT adiabatic approximation, the use of which in photochemical applications mu...

Benchmark full configuration interaction 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 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.

Article Outline

INTRODUCTION
METHODOLOGY
1. EOM-CC approach to open-shell and electronically excited species
2. Generalized Mulliken-Hush model
3. The CT reaction coordinates
4. Computational details
RESULTS AND DISCUSSION
1. (He₂)⁺ dimer
2. (H₂)2+ dimer
3. (Be–BH)⁺ dimer
4. (BH–H₂)⁺ dimer
5. (LiH)2+ dimer
6. (C₂H₄)2+
CONCLUSIONS

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KEYWORDS and PACS

Keywords

configuration interactions, coupled cluster calculations, potential energy surfaces

PACS

31.15.V-

Electron correlation calculations for atoms, ions and molecules
31.15.bw

Coupled-cluster theory
31.50.-x

Potential energy surfaces

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http://link.aip.org/link/doi/10.1063/1.2795709

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0021-9606 (print)

1089-7690 (online)

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American Institute of Physics

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