Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Kimber, Patrick; Plasser, Felix

doi:10.1039/d0cp00369g

Cited by 78 publications

(149 citation statements)

References 149 publications

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“…The TheoDORE 2.2 program 93,94 was used for this purpose, through the analysis of the one-particle transition density matrix 95,96 which will also allow for the comparison with existing data. For the weakly bound (inter-molecular) CT complexes, each of the weakly interacting molecules of the complex is defined as a fragment to carry out the exciton analysis using the following descriptors [97][98][99] As a benchmarking case, the metrics computed for the benzene-TCNE example (Ω POS = 1.50 and Ω CT = 0.98, for all the DH methods) perfectly agrees with those calculated from an in-depth analysis of the linear response TD-DFT transition density matrix 43 : a negligible orbital overlap between the frontier molecular orbitals (the S 1 S 0 excitation is a π !…”

Section: Identification Of Charge-transfer Statesmentioning

confidence: 99%

Assessing challenging intra‐ and inter‐molecular charge‐transfer excitations energies with double‐hybrid density functionals

et al. 2021

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We investigate the performance of a set of recently introduced range-separated double-hybrid functionals, namely ωB2-PLYP, ωB2GP-PLYP, RSX-0DH, and RSX-QIDH models for hard-to-calculate excitation energies. We compare with the parent (B2-PLYP, B2GP-PLYP, PBE0-DH, and PBE-QIDH) and other (DSD-PBEP86) doublehybrid models as well as with some of the most widely employed hybrid functionals (B3LYP, PBE0, M06-2X, and ωB97X). For this purpose, we select a number of medium-sized intra-and inter-molecular charge-transfer excitations, which are known to be challenging to calculate using time-dependent density-functional theory (TD-DFT) and for which accurate reference values are available. We assess whether the high accuracy shown by the newest double-hybrid models is also confirmed for those cases too. We find that asymptotically corrected double-hybrid models yield a superior performance, especially for the inter-molecular charge-transfer excitation energies, as compared to standard double-hybrid models. Overall, the PBE-QIDH and its corresponding range-separated RSX-QIDH functional are recommended for general-purpose TD-DFT applications, depending on whether long-range effects are expected to play a significant role.

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Section: Identification Of Charge-transfer Statesmentioning

confidence: 99%

Assessing challenging intra‐ and inter‐molecular charge‐transfer excitations energies with double‐hybrid density functionals

et al. 2021

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“…This issue is further explored here, hopefully complementing previous studies [20,21] after inspecting first the corresponding theoretical expression in which the TD‐DFT singlet‐triplet gap is based. Additionally, we will try to provide insights, beyond the one‐electron molecular picture, [31] to understand why (highly) correlated methods are able to cope with the underlying electronic structure of these systems, and thus predicting the correct order and energy of excited‐states, contrarily to what happens with TD‐DFT. This theoretical understanding could pave the way towards the theoretical design of other closed‐shell organic molecules with inverted excited‐states and therefore with prospects in optoelectronic and photocatalytic applications.…”

Section: Introductionmentioning

confidence: 99%

Singlet‐Triplet Excited‐State Inversion in Heptazine and Related Molecules: Assessment of TD‐DFT and ab initio Methods

et al. 2021

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We have investigated the origin of the S1‐T1 energy levels inversion for heptazine, and other N‐doped π‐conjugated hydrocarbons, leading thus to an unusually negative singlet‐triplet energy gap (ΔEST<0 ). Since this inversion might rely on substantial doubly‐excited configurations to the S1 and/or T1 wavefunctions, we have systematically applied multi‐configurational SA‐CASSCF and SC‐NEVPT2 methods, SCS‐corrected CC2 and ADC(2) approaches, and linear‐response TD‐DFT, to analyze if the latter method could also face this challenging issue. We have also extended the study to B‐doped π‐conjugated systems, to see the effect of chemical composition on the results. For all the systems studied, an intricate interplay between the singlet‐triplet exchange interaction, the influence of doubly‐excited configurations, and the impact of dynamic correlation effects, serves to explain the ΔEST<0 values found for most of the compounds, which is not predicted by TD‐DFT.

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“…From a more formal viewpoint it is worth pointing out that there is a specific hierarchy between frontier orbitals, biradical character/NTOs, and the shielding tensors. Frontier orbitals are simply intermediates in approximate theories and it is well-known that their shapes and energies change dramatically with the level of theory chosen [47,75]. Measures for biradical character and the NTOs can be defined based on the wavefunctions alone [24,66,76] and are, thus, well-defined without any explicit reference to a computational level of theory.…”

Section: Discussionmentioning

confidence: 99%

Exploitation of Baird Aromaticity and Clar's Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

Plasser

2021

Preprint

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Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four PAHs based on the biphenylene motif finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). These results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

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Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Abstract: Can we gain an intuitive understanding of excitation energies beyond the molecular picture?

Cited by 78 publications

References 149 publications

Assessing challenging intra‐ and inter‐molecular charge‐transfer excitations energies with double‐hybrid density functionals

Assessing challenging intra‐ and inter‐molecular charge‐transfer excitations energies with double‐hybrid density functionals

Singlet‐Triplet Excited‐State Inversion in Heptazine and Related Molecules: Assessment of TD‐DFT and ab initio Methods

Exploitation of Baird Aromaticity and Clar's Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

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