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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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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Accurate and efficient prediction of double excitation energies using the particle–particle random phase approximation

The Journal of Chemical Physics, Journal Year: 2025, Volume and Issue: 162(9)

Published: March 3, 2025

Double excitations are crucial to understanding numerous chemical, physical, and biological processes, but accurately predicting them remains a challenge. In this work, we explore the particle–particle random phase approximation (ppRPA) as an efficient accurate approach for computing double excitation energies. We benchmark ppRPA using various exchange-correlation functionals 21 molecular systems two point defect systems. Our results show that with containing appropriate amounts of exact exchange provides accuracy comparable high-level wave function methods such CCSDT CASPT2, significantly reduced computational cost. Furthermore, demonstrate use starting from excited (N − 2)-electron state calculated by ΔSCF first time, well its application in bulk periodic These findings suggest is promising tool calculation partial energies both

Language: Английский

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Range‐Separated Density Functionals in Predicting Correct Excitation Energies in Gas and Solvent Continuum: A Benchmark Investigation on a Large Set of Molecules

International Journal of Quantum Chemistry, Journal Year: 2025, Volume and Issue: 125(7)

Published: March 18, 2025

ABSTRACT Computationally cost‐effective methods with high accuracy are indispensable in the field of quantum chemistry. Recently, descriptor‐based tuning range‐separated (RS) functionals have attracted theoreticians because their improved performance computing various chemical properties. In this article, we assessed our newly developed electron localization function (ELF) tuned [ J. Comput. Chem. 2017 , 38 2258] and solvent (Sol) 2020 41 295] RS calculation lowest singlet vertical excitation energies a large set molecules gas continuum. Moreover, EOM‐CCSD benchmark values been generated solvents. Notably, under influence continuum computed using perturbation theory density approach (PTED) to take care effects calculations. This study envisages that ELF Sol‐tuned can accurately reproduce values. Furthermore, predict decrease polarity, which is consistent results.

Language: Английский

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Improving Aufbau Suppressed Coupled Cluster through Perturbative Analysis

Journal of Chemical Theory and Computation, Journal Year: 2025, Volume and Issue: unknown

Published: April 10, 2025

Guided by perturbative analysis, we improve the accuracy of Aufbau suppressed coupled cluster theory in simple single excitations, multiconfigurational and charge transfer excitations while keeping cost its leading-order terms precisely line with ground-state cluster. Combining these improvements a more efficient implementation based on spin adaptation, observe high large test set and, particular, mean unsigned error for states that outperforms equation-of-motion 0.25 eV. We discuss how results are achieved via systematic identification which amplitudes to prioritize single- excited states, this prioritization differs important ways from theory. In our data show partial linearization increases mitigating unwanted side effects suppression.

Language: Английский

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Equation-of-motion internally contracted multireference unitary coupled-cluster theory

The Journal of Chemical Physics, Journal Year: 2025, Volume and Issue: 162(15)

Published: April 16, 2025

The accurate computation of excited states remains a challenge in electronic structure theory, especially for systems with ground state that requires multireference treatment. In this work, we introduce novel equation-of-motion (EOM) extension the internally contracted unitary coupled-cluster framework (ic-MRUCC), termed EOM-ic-MRUCC. EOM-ic-MRUCC follows transform-then-diagonalize approach, analogy to its non-unitary counterpart [Datta and Nooijen, J. Chem. Phys. 137, 204107 (2012)]. By employing projective approach optimize state, method retains additive separability proper scaling system size. We show excitation energies are size-intensive if EOM operator satisfies “killer” conditions. Furthermore, propose represent changes reference upon electron via projected many-body operators span active orbitals equations formulated way invariant respect orbital rotations. test truncated single double excitations by computing potential energy curves several BeH2 model system, HF molecule, water undergoing symmetric dissociation. Across these systems, our delivers within 5 mEh (∼0.14 eV) from full configuration interaction. find truncating Baker–Campbell–Hausdorff series fourfold commutators contributes negligible errors (on order 10−5Eh or less), offering practical route highly excited-state calculations reduced computational overhead.

Language: Английский

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Excited-state methods for molecular systems: Performance, pitfalls, and practical guidance

Chemical Physics Reviews, Journal Year: 2025, Volume and Issue: 6(2)

Published: May 1, 2025

Proper theoretical descriptions of ground and excited states are critical for understanding molecular photophysics photochemistry. Complex interactions in experimentally interesting systems require multiple approximations the underlying quantum mechanics to practically solve various physical observables. While high-level calculations small provide very accurate excitation energies, this accuracy does not always extend larger or other properties. Because this, “best” method study new molecules is clear, leading many researchers default inexpensive easy-to-use black-box methods. Unfortunately, even when these methods reproduce experimental it necessarily right reasons. Without physics, becomes challenging understand classes molecules. Consequently, predicted properties their trends may offer reliable mechanistic understanding. This review targeted at beginners computational chemistry who interested studying excited-state A brief overview common ground- covered easy reference during comparison The primary focus compare several important chromophores. performance each explored practitioners a road map on what work well different identify further that needs be done field.

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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∆DFT predicts inverted singlet-triplet gaps with chemical accuracy at a fraction of the cost of wavefunction-based approaches

Published: June 3, 2024

Efficient OLEDs must 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 wavefunction-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 to 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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Calculation of Low-Lying Electronic Excitations of Magnesium Monofluoride: How Well Do Coupled-Cluster Methods Work?

Atoms, Journal Year: 2024, Volume and Issue: 12(8), P. 40 - 40

Published: Aug. 8, 2024

Magnesium monofluoride is a polar molecule amenable to laser cooling which has caused renewed interest in its spectroscopy. In this work, we consider the case of three low-lying electronic excitations, namely X2Σ+→A2Π, X2Σ+→B2Σ+, X2Σ+→C2Σ+, using well-developed quantum chemistry approaches, i.e., without reference spin-orbit splitting A2Π states. Accurate experimental data for these transitions have been available over 50 years. Here, explore linear response method at level CC2 theory, as well equation motion methods CCSD and CC3, two families basis sets. Excellent agreement obtained first when correlation-consistent sets extrapolation complete limit within EOM-CC3 (at relative precision 10−4), qualitative other methods. The purpose paper serve guide on how approach accurate calculation excitations diatomic molecules.

Language: Английский

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