The intermediate state approach for doubly excited dark states in EOM-coupled-cluster theory

Ravi, Moneesha; Park, Young Choon; Perera, Ajith; Bartlett, Rodney J.

doi:10.1063/5.0091715

Cited by 13 publications

(11 citation statements)

References 37 publications

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“…Further improvement for ΔCCSD calculations could likely be achieved by using alternative single determinant reference for the excited state, either tailored or not as in or intermediate state (IS) approach. 9 Compared to ΔCCSD, we speculate that single-reference approximations that are more suited for a strong correlation problem such as DCSD and pCCD might perform better. However, there are still sufficient convergence issues for DCSD and pCCD to prevent access to all the states.…”

Section: Effect Of Perturbative Triples: Eom-ccsd(t) Compared With Eo...mentioning

confidence: 93%

“…The basis set used is the modest 6-31G(d) for comparison to prior work. For the QUEST2 benchmark set, optimized geometries and reference results for CC3, CASPT2 and exFCI (selected CI + PT2) were taken from the work of Loos et al , These exFCI results are referred to here as the theoretical best estimates (TBE), although we would argue that EOM-CCSDTQ would be a better measure, especially with more flexible basis sets …”

Section: Methodsmentioning

confidence: 99%

“…For such states, the errors for EOM-CCSD compared to full CI are above ∼0.5 eV and have been shown to be as much as ∼6 eV. 9 In earlier studies, it has been argued that the relaxation of EOM-CC amplitudes, R 2 in the presence of R 3 , is essential for improved performance of these methods as could be seen by the success of the EOM-CC(2,3) method 10 which treats the ground state with CCSD, but then diagonalizes the similarity transformed Hamiltonian over the singles (S), doubles (D), and triples (T) excitation space. The latter is the critical effect, but it makes the diagonalization step more demanding.…”

Section: ■ Introductionmentioning

confidence: 99%

“…But when used for pure doubly excited states or even for some states which involve a significant admixture of singly and doubly excited states, , truncation to only singles and doubles is inadequate. For such states, the errors for EOM-CCSD compared to full CI are above ∼0.5 eV and have been shown to be as much as ∼6 eV . In earlier studies, it has been argued that the relaxation of EOM-CC amplitudes, R 2 in the presence of R 3 , is essential for improved performance of these methods as could be seen by the success of the EOM-CC(2,3) method which treats the ground state with CCSD, but then diagonalizes the similarity transformed Hamiltonian over the singles (S), doubles (D), and triples (T) excitation space.…”

Section: Introductionmentioning

confidence: 99%

“…That is the same as pCCD+TCCSD. These approaches, particularly the ground state treatment, also lie very much in the broad category of tailored or externally corrected methods. , Loos and co-workers have recently shown that orbital optimized ΔpCCD offers significant improvement over just EOM-CCSD when used in a state specific manner, though the study was limited to a small subset of doubly excited states. , Our recent work introduces the use of intermediate (singly) excited states as the reference to access doubly excited states through EOM-CC calculations and found the results to be very accurate.…”

Section: Introductionmentioning

confidence: 99%

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Dark Doubly Excited States with Modified Coupled Cluster Models: A Reliable Compromise between Cost and Accuracy?

et al. 2023

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To treat doubly excited states, the treatment of triple excitations is considered necessary in the framework of equation-of-motion coupled cluster (EOM-CC) methods. We investigate models without explicit triples and seek quantitative measure for the performance of EOM based on CC with singles and doubles (CCSD) or modified CCSD (Distinguishable Cluster Approximation) approaches for states with predominant double excitation character. We also test the efficacy of including triples in perturbative manner through EOM-CCSD(T) and in an iterative way through EOM-CCSDT-3 method. Extended similarity transformed EOM-CCSD(EXT-STEOM-CCSD) method is also tested and provides superior quality results at comparatively low cost. We use the QUEST2 benchmark set of double excitations proposed by Loos et al. [J. Chem. Theory Comput.2019151939] to investigate the performance of methods such as EOM-CCSD, EOM-DCSD, EXT-STEOM-CCSD, ΔCCSD, and ΔDCSD. We also test a tailored CC approach, ΔpairCCD-TCCSD.

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Section: Effect Of Perturbative Triples: Eom-ccsd(t) Compared With Eo...mentioning

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dark Doubly Excited States with Modified Coupled Cluster Models: A Reliable Compromise between Cost and Accuracy?

et al. 2023

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Spectroscopy of End-On Copper(II) Superoxido Complexes: A Wave Function-Based Analysis

Chaussy,

Chilkuri,

Humbel

et al. 2024

Inorg. Chem.

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Wave function methods are employed to analyze the ground and low-lying excited states of bipyramid trigonal copper(II) superoxido complexes, up to their characteristic ligand to metal charge transfer band. Several multireference methods have been combined to provide new insights into the interpretation of their experimental absorption spectra. We show that the intraligand transition on the dioxygen leads to a dark state. Among the results, we shall highlight the finding of doubly excited states in the region of the d−d transitions and the subtle interplay between Cu(I) and Cu(II) in the ground and excited states. Some of these findings could be obtained only with multireference methods.

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State-Specific Coupled-Cluster Methods for Excited States

Damour,

Scemama,

Jacquemin

et al. 2024

J. Chem. Theory Comput.

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We reexamine ΔCCSD, a state-specific coupledcluster (CC) with single and double excitations (CCSD) approach that targets excited states through the utilization of non-Aufbau determinants. This methodology is particularly efficient when dealing with doubly excited states, a domain in which the standard equation-of-motion CCSD (EOM-CCSD) formalism falls short. Our goal here to evaluate the effectiveness of ΔCCSD when applied to other types of excited states, comparing its consistency and accuracy with EOM-CCSD. To this end, we report a benchmark on excitation energies computed with the ΔCCSD and EOM-CCSD methods for a set of molecular excited-state energies that encompasses not only doubly excited states but also doublet− doublet transitions and (singlet and triplet) singly excited states of closed-shell systems. In the latter case, we rely on a minimalist version of multireference CC known as the two-determinant CCSD method to compute the excited states. Our data set, consisting of 276 excited states stemming from the QUEST database [Veŕil et al., WIREs Comput. Mol. Sci. 2021, provides a significant base to draw general conclusions concerning the accuracy of ΔCCSD. Except for the doubly excited states, we found that ΔCCSD underperforms EOM-CCSD. For doublet−doublet transitions, the difference between the mean absolute errors (MAEs) of the two methodologies (of 0.10 and 0.07 eV) is less pronounced than that obtained for singly excited states of closed-shell systems (MAEs of 0.15 and 0.08 eV). This discrepancy is largely attributed to a greater number of excited states in the latter set exhibiting multiconfigurational characters, which are more challenging for ΔCCSD. We also found typically small improvements by employing state-specific optimized orbitals.

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The intermediate state approach for doubly excited dark states in EOM-coupled-cluster theory

Cited by 13 publications

References 37 publications

Dark Doubly Excited States with Modified Coupled Cluster Models: A Reliable Compromise between Cost and Accuracy?

Dark Doubly Excited States with Modified Coupled Cluster Models: A Reliable Compromise between Cost and Accuracy?

Spectroscopy of End-On Copper(II) Superoxido Complexes: A Wave Function-Based Analysis

State-Specific Coupled-Cluster Methods for Excited States

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