Mountaineering Strategy to Excited States: Highly Accurate Energies and Benchmarks for Exotic Molecules and Radicals

Loos, Pierre‐François; Scemama, Anthony; Boggio‐Pasqua, Martial; Jacquemin, Denis

doi:10.1021/acs.jctc.0c00227

Cited by 96 publications

(201 citation statements)

References 182 publications

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“…Obviously, some systems treated here have been taken from the sets described above, but we have both computed more accurate geometries (vide infra) and clearly increased the level of theory employed to define the benchmark TBEs as compared to previous efforts devoted to intramolacular CT. Although these endeavors are well in-line with our recent efforts devoted to local and Rydberg transitions of organic compounds [93][94][95][96] that led to the QUEST database encompassing approximately 500 reference vertical transition energies, 39,90 it should be noted that the very nature of CT transitions makes the determination of reference values more challenging. Indeed, large density shifts ubiquitous to CT phenomena typically take place in larger compounds than those previously treated.…”

Section: Literature Surveymentioning

confidence: 73%

Reference Energies for Double Excitations

Loos

Boggio‐Pasqua

Scemama

et al. 2019

J. Chem. Theory Comput.

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182

378

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Excited states exhibiting double excitation character are notoriously di cult to model using conventional singlereference methods, such as adiabatic time-dependent density-functional theory (TD-DFT) or equation-of-motion coupled cluster (EOM-CC). In addition, these states are typical experimentally "dark" making their detection in photo-absorption spectra very challenging. Nonetheless, they play a key role in the faithful description of many physical, chemical, and biological processes. In the present work, we provide accurate reference excitation energies for transitions involving a substantial amount of double excitation using a series of increasingly large di use-containing atomic basis sets. Our set gathers 20 vertical transitions from 14 small-and medium-size molecules (acrolein, benzene, beryllium atom, butadiene, carbon dimer and trimer, ethylene, formaldehyde, glyoxal, hexatriene, nitrosomethane, nitroxyl, pyrazine, and tetrazine). Depending on the size of the molecule, selected con guration interaction (sCI) and/or multicon gurational (CASSCF, CASPT2, (X)MS-CASPT2 and NEVPT2) calculations are performed in order to obtain reliable estimates of the vertical transition energies. In addition, coupled cluster approaches including at least contributions from iterative triples (such as CC3, CCSDT, CCSDTQ, and CCSDTQP) are assessed. Our results clearly evidence that the error in CC methods is intimately related to the amount of double excitation character of the transition. For "pure" double excitations (i.e. for transitions which do not mix with single excitations), the error in CC3 can easily reach 1 eV, while it goes down to few tenths of an eV for more common transitions (like in trans-butadiene) involving a signi cant amount of singles. As expected, CC approaches including quadruples yield highly accurate results for any type of transitions. e quality of the excitation energies obtained with multicon gurational methods is harder to predict. We have found that the overall accuracy of these methods is highly dependent of both the system and the selected active space. e inclusion of the σ and σ orbitals in the active space, even for transitions involving mostly π and π orbitals, is mandatory in order to reach high accuracy. A theoretical best estimate (TBE) is reported for each transition. We believe that these reference data will be valuable for future methodological developments aiming at accurately describing double excitations. TOC graphical abstract arXiv:1811.12861v1 [physics.chem-ph] 30 Nov 2018

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Section: Literature Surveymentioning

confidence: 73%

Reference Energies for Double Excitations

Loos

Boggio‐Pasqua

Scemama

et al. 2019

J. Chem. Theory Comput.

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182

378

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“…In the present review article, we have presented and extended the QUEST database of highly accurate excitation energies for molecular systems 15, 93–96 that we started building in 2018 and that is now composed by more than 500 vertical excitations, many of which can be reasonably considered as within 1 kcal/mol (or less) of the FCI limit for the considered CC3/ aug ‐cc‐pVTZ geometry and basis set ( aug ‐cc‐pVTZ). In particular, we have detailed the specificities of our protocol by providing computational details regarding geometries, basis sets, as well as reference and benchmarked computational methods.…”

Section: Discussionmentioning

confidence: 99%

“…Quite a large number of calculations were required for each of the QUEST articles 93–96, 212 . Up to now, all the curated data were shared as supplementary information presented as a file in portable document format.…”

Section: The Questdb Websitementioning

confidence: 99%

“…Following a similar philosophy and striving for chemical accuracy, we have recently reported in several studies highly accurate vertical excitations for small‐ and medium‐sized molecules 15, 93–96 . The so‐called QUEST dataset of vertical excitations which we will describe in detail in the present review article is composed by 5 subsets (see Figure 1): (i) a subset of excitations in small molecules containing from 1 to 3 non‐hydrogen atoms known as QUEST#1, (ii) a subset of double excitations in molecules of small and medium sizes known as QUEST#2, (iii) a subset of excitation energies for medium‐sized molecules containing from 4 to 6 non‐hydrogen atoms known as QUEST#3, (iv) a subset composed by more “exotic” molecules and radicals labeled as QUEST#4, and (v) a subset known as QUEST#5, specifically designed for the present article, gathering excitation energies in larger molecules as well as additional smaller molecules.…”

Section: Introductionmentioning

confidence: 99%

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QUESTDB: A database of highly accurate excitation energies for the electronic structure community

Véril

Scemama

Caffarel

et al. 2021

WIREs Comput Mol Sci

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149

303

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We describe our efforts of the past few years to create a large set of more than 500 highly accurate vertical excitation energies of various natures (π → π*, n → π*, double excitation, Rydberg, singlet, doublet, triplet, etc.) in small‐ and medium‐sized molecules. These values have been obtained using an incremental strategy which consists in combining high‐order coupled cluster and selected configuration interaction calculations using increasingly large diffuse basis sets in order to reach high accuracy. One of the key aspects of the so‐called QUEST database of vertical excitations is that it does not rely on any experimental values, avoiding potential biases inherently linked to experiments and facilitating theoretical cross comparisons. Following this composite protocol, we have been able to produce theoretical best estimates (TBEs) with the aug‐cc‐pVTZ basis set for each of these transitions, as well as basis set corrected TBEs (i.e., near the complete basis set limit) for some of them. The TBEs/aug‐cc‐pVTZ have been employed to benchmark a large number of (lower‐order) wave function methods such as CIS(D), ADC(2), CC2, STEOM‐CCSD, CCSD, CCSDR(3), CCSDT‐3, ADC(3), CC3, NEVPT2, and so on (including spin‐scaled variants). In order to gather the huge amount of data produced during the QUEST project, we have created a website (https://lcpq.github.io/QUESTDB_website) where one can easily test and compare the accuracy of a given method with respect to various variables such as the molecule size or its family, the nature of the excited states, the type of basis set, and so on. We hope that the present review will provide a useful summary of our effort so far and foster new developments around excited‐state methods. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods

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“…Like adiabatic time-dependent density-functional theory (TD-DFT), 46 − 49 the static BSE formalism is plagued by the lack of double (and higher) excitations, which are, for example, ubiquitous in conjugated molecules like polyenes 50 − 57 or the ground state of open-shell molecules. 58 − 60 Indeed, both adiabatic TD-DFT 61 − 65 and static BSE 66 − 70 can only access (singlet and triplet) single excitations with respect to the reference determinant usually taken as the closed-shell singlet ground state. Double excitations are even challenging for state-of-the-art methods, 11 , 57 , 71 − 73 like the approximate third-order coupled-cluster (CC3) method 74 , 75 or equation-of-motion coupled-cluster with singles, doubles, and triples (EOM-CCSDT).…”

Section: Introductionmentioning

confidence: 99%

Spin-Conserved and Spin-Flip Optical Excitations from the Bethe–Salpeter Equation Formalism

Monino

Loos

2021

J. Chem. Theory Comput.

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Like adiabatic time-dependent density-functional theory (TD-DFT), the Bethe–Salpeter equation (BSE) formalism of many-body perturbation theory, in its static approximation, is “blind” to double (and higher) excitations, which are ubiquitous, for example, in conjugated molecules like polyenes. Here, we apply the spin-flip ansatz (which considers the lowest triplet state as the reference configuration instead of the singlet ground state) to the BSE formalism in order to access, in particular, double excitations. The present scheme is based on a spin-unrestricted version of the GW approximation employed to compute the charged excitations and screened Coulomb potential required for the BSE calculations. Dynamical corrections to the static BSE optical excitations are taken into account via an unrestricted generalization of our recently developed (renormalized) perturbative treatment. The performance of the present spin-flip BSE formalism is illustrated by computing excited-state energies of the beryllium atom, the hydrogen molecule at various bond lengths, and cyclobutadiene in its rectangular and square-planar geometries.

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Mountaineering Strategy to Excited States: Highly Accurate Energies and Benchmarks for Exotic Molecules and Radicals

Cited by 96 publications

References 182 publications

Reference Energies for Double Excitations

Reference Energies for Double Excitations

QUESTDB: A database of highly accurate excitation energies for the electronic structure community

Spin-Conserved and Spin-Flip Optical Excitations from the Bethe–Salpeter Equation Formalism

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