Electronic structure of norbornadiene and quadricyclane

Physical Chemistry Chemical Physics, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 1, 2025

The ground and excited state electronic structure of the molecular photoswitches quadricyclane norbornadiene is examined qualitatively quantitatively.

Language: Английский

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Energy Component Analysis for Electronically Excited States of Molecules: Why the Lowest Excited State Is Not Always the HOMO/LUMO Transition

Journal of Chemical Theory and Computation, Journal Year: 2023, Volume and Issue: 19(8), P. 2340 - 2352

Published: April 6, 2023

The ability to tune excited-state energies is crucial many areas of molecular design. In cases, this done based on the highest occupied orbital (HOMO) and lowest unoccupied (LUMO). However, viewpoint incomplete neglecting many-body nature underlying wave functions. Within work, we highlight importance two terms, other than energies, that contribute excitation show how quantify them from quantum chemistry computations: a Coulomb attraction repulsive exchange interaction. Using framework, explain under which circumstances excited state molecule, either singlet or triplet multiplicity, not accessed via HOMO/LUMO transition paradigmatic examples. case push-pull molecule ACRFLCN, locally lying below charge transfer due enhanced binding. naphthalene (the 1La state) becomes second its repulsion term. More generally, why do always behave like energy gaps, providing insight into photophysical processes as well methodogical challenges in describing them.

Language: Английский

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Reference Energies for Valence Ionizations and Satellite Transitions

Journal of Chemical Theory and Computation, Journal Year: 2024, Volume and Issue: 20(11), P. 4751 - 4777

Published: May 22, 2024

Upon ionization of an atom or a molecule, another electron (or more) can be simultaneously excited. These concurrently generated states are called "satellites" shakeup transitions) as they appear in spectra higher-energy peaks with weaker intensity and larger width than the main associated single-particle ionizations. Satellites, which correspond to electronically excited cationic species, notoriously challenging model using conventional single-reference methods due their high excitation degree compared neutral reference state. This work reports 42 satellite transition energies 58 valence potentials (IPs) full configuration interaction quality computed small molecular systems. Following protocol developed for quest database [Véril, M.; Scemama, A.; Caffarel, Lipparini, F.; Boggio-Pasqua, Jacquemin, D.; Loos, P.-F. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2021, 11, e1517], these perturbative selection made iteratively (CIPSI) method. In addition, accuracy well-known coupled-cluster (CC) hierarchy (CC2, CCSD, CC3, CCSDT, CC4, CCSDTQ) is gauged against new accurate references. The performances various approximations based on many-body Green's functions (GW, GF2, T-matrix) IPs also analyzed. Their limitations correctly modeling transitions discussed.

Language: Английский

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State-Specific Coupled-Cluster Methods for Excited States

Journal of Chemical Theory and Computation, Journal Year: 2024, Volume and Issue: 20(10), P. 4129 - 4145

Published: May 15, 2024

We reexamine ΔCCSD, a state-specific coupled-cluster (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 doubly states, domain in which standard equation-of-motion CCSD (EOM-CCSD) formalism falls short. Our goal here to evaluate effectiveness ΔCCSD applied other types comparing its consistency accuracy EOM-CCSD. To this end, we report benchmark on excitation energies computed EOM-CCSD methods for set molecular excited-state encompasses not only but also doublet–doublet transitions (singlet triplet) singly closed-shell systems. In latter case, rely minimalist version multireference CC known as two-determinant method compute states. data set, consisting 276 stemming from quest database [Véril et al., WIREs Comput. Mol. Sci. 2021, 11, e1517], provides significant base draw general conclusions concerning ΔCCSD. Except found underperforms For transitions, difference between mean absolute errors (MAEs) two methodologies (of 0.10 0.07 eV) less pronounced than obtained systems (MAEs 0.15 0.08 eV). discrepancy largely attributed greater number exhibiting multiconfigurational characters, are more challenging typically small improvements by employing optimized orbitals.

Language: Английский

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Reference Energies for Double Excitations: Improvement and Extension

Journal of Chemical Theory and Computation, Journal Year: 2024, Volume and Issue: 20(13), P. 5655 - 5678

Published: June 17, 2024

In the realm of photochemistry, significance double excitations (also known as doubly excited states), where two electrons are concurrently elevated to higher energy levels, lies in their involvement key electronic transitions essential light-induced chemical reactions well challenging nature from computational theoretical chemistry point view. Based on state-of-the-art structure methods (such high-order coupled-cluster, selected configuration interaction, and multiconfigurational methods), we improve expand our prior set accurate reference excitation energies for states exhibiting a substantial amount [Loos et al. J. Chem. Theory Comput. 2019, 15, 1939]. This extended collection encompasses 47 across 26 molecular systems that separate into distinct subsets: (i) 28 "genuine" almost exclusively involve configurations (ii) 19 "partial" which exhibit more balanced character between singly configurations. For each subset, assess performance coupled-cluster (CC3, CCSDT, CC4, CCSDTQ) (CASPT2, CASPT3, PC-NEVPT2, SC-NEVPT2). Using probe percentage single involved given transition (%T1) computed at CC3 level, also propose simple correction reduces errors by factor 3, both sets excitations. We hope this complete diverse compilation will help future developments excited-state methodologies.

Language: Английский

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Energy Decomposition Analysis for excited states: An Extension based on TDDFT

Physical Chemistry Chemical Physics, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 1, 2025

Energy decomposition analysis (EDA) is extended by the excited state EDA (exc-EDA) using time-dependent density functional theory (TDDFT). Validated through studies on exciplexes, it demonstrates utility singlet fission in pentacene.

Language: Английский

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ΔDFT Predicts Inverted Singlet–Triplet Gaps with Chemical Accuracy at a Fraction of the Cost of Wave Function-Based Approaches

The Journal of Physical Chemistry Letters, Journal Year: 2024, Volume and Issue: 15(31), P. 8065 - 8077

Published: July 31, 2024

Efficient OLEDs need to quickly convert singlet and triplet excitons into photons. Molecules with an inverted singlet–triplet energy gap (INVEST) are promising candidates for this task. However, typical INVEST molecules have drawbacks like too low oscillator strengths excitation energies. High-throughput screening could identify suitable molecules, but existing methods problematic: The workhorse method TD-DFT cannot reproduce inversion, while wave function-based slow. This study proposes a state-specific based on unrestricted Kohn–Sham DFT common hybrid functionals. Tuned the new INVEST15 benchmark set, achieves error of less than 1 kcal/mol, which is traced back cancellation between spin contamination dynamic correlation. Applied larger structurally diverse NAH159 set in black-box fashion, maintains small (1.2 kcal/mol) accurately predicts signs 83% cases, confirming its robustness suitability workflows.

Language: Английский

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On the Meaning of De‐Excitations in Time‐Dependent Density Functional Theory Computations

Journal of Computational Chemistry, Journal Year: 2025, Volume and Issue: 46(8)

Published: March 25, 2025

De-excitations play a prominent role within the mathematical formalism of time-dependent density functional theory (TDDFT) and other excited-state response methods. However, their physical meaning remains largely unexplored poorly understood. It is purpose this work to shed new light on issue. The main thesis developed here that de-excitations are not peculiarity TDDFT but they more fundamental property underlying wave functions reflecting how electrons excited between partially occupied orbitals. paraquinodimethane (pQDM) molecule chosen as convenient model system whose open-shell character can be modulated via twisting its methylene groups. Using one-electron transition matrix rigorous basis for our analysis, we highlight qualitative quantitative parallels in way reflected multireference function computations. As physically observable consequence, lowering dipole moment derives from destructive interference excitation de-excitation contributions. In summary, hope will formal practical aspects regarding application computations, especially diradicaloid systems.

Language: Английский

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Low-lying excited states of linear all-trans polyenes: the σ–π electron correlation and the description of ionic states

Physical Chemistry Chemical Physics, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 1, 2025

Accurately describing ionic states requires addressing basis-set effects, size-extensivity errors, and, most importantly, σ–π electron correlation.

Language: Английский

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Methods for identifying electronically coherent states via degeneracy and conjugation in organic molecules using DFT studies

Advances in quantum chemistry, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 1, 2025

Language: Английский

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