W4Λ: Leveraging Λ Coupled-Cluster for Accurate Computational Thermochemistry Approaches

Semidalas, Emmanouil; Karton, Amir; Martin, Jan M. L.

doi:10.1021/acs.jpca.3c08158

Cited by 3 publications

(2 citation statements)

References 66 publications

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“…When more accurate results are sought or multireference systems are investigated, full triples and (perturbatively, possibly with the improved Λ scheme) quadruple excitations are added by conventional CC computations employing the cc-pVTZ and cc-pVDZ basis set, respectively. In such circumstances, the PCS4 version (not analyzed in detail in the present context) can be used, which employs the standard 3F12, 4F12 and (for the MP2-F12 part) 5F12 basis sets for the valence energy and the wC3 and wC4 basis sets for the CV correlation.…”

Section: Methodsmentioning

confidence: 99%

Toward Accurate Quantum Chemical Methods for Molecules of Increasing Dimension: The New Family of Pisa Composite Schemes

Di Grande,

Barone

2024

J. Phys. Chem. A

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The new versions of the Pisa composite scheme introduced in the present paper are based on the careful selection of different quantum chemical models for energies, geometries, and vibrational frequencies, with the aim of maximizing the accuracy of the overall description while retaining a reasonable cost for all the steps. In particular, the computation of accurate electronic energies has been further improved introducing more reliable complete basis set extrapolations and estimation of core−valence correlation, together with improved basis sets for third-row atoms. Furthermore, the reduced-cost frozen natural orbital (FNO) model has been introduced and validated for large molecules. Accurate molecular structures can be obtained avoiding complete basis set extrapolation and evaluating core−valence correlation at the MP2 level. Unfortunately, analytical gradients are not available for the FNO version of the model. Therefore, for large molecules, an accurate reduced-cost alternative is offered by evaluation of valence contributions with a double-hybrid functional in conjunction with the same MP2 contribution for core−valence correlation or by means of a one-parameter approximation. The same doublehybrid functional and basis set are employed to evaluate zero-point energies and partition functions. After the validation of the new models for small systems, a panel of molecular bricks of life has been used to analyze their performances for problems of current fundamental or technological interest. The fully black-box implementation of the computational workflow paves the way toward the accurate yet not prohibitively expensive study of medium-to large-sized molecules also by experimentally oriented researchers.

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Section: Methodsmentioning

confidence: 99%

Toward Accurate Quantum Chemical Methods for Molecules of Increasing Dimension: The New Family of Pisa Composite Schemes

Di Grande,

Barone

2024

J. Phys. Chem. A

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“…It is fairly well established that the CCSDT(Q) method overestimates the quadruples increment to the electron correlation energy of ozone and Criegee intermediates. − This issue can be improved by using the fully iterative quadruple Q (or higher order) electron correlation method. Recent studies show that the (Q) Λ calculation, which is much cheaper than the full Q calculation, can provide a comparable accuracy for such a case . For this reason, in this work both HEAT-345Q and HEAT-345(Q) Λ methods are used.…”

mentioning

confidence: 99%

Nonstatistical Unimolecular Decay of the CH₂OO Criegee Intermediate in the Tunneling Regime

Qian,

Nguyen,

Franke

et al. 2024

J. Phys. Chem. Lett.

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Unimolecular decay of the formaldehyde oxide (CH 2 OO) Criegee intermediate proceeds via a 1,3 ring-closure pathway to dioxirane and subsequent rearrangement and/or dissociation to many products including hydroxyl (OH) radicals that are detected. Vibrational activation of jet-cooled CH 2 OO with two quanta of CH stretch (17−18 kcal mol −1 ) leads to unimolecular decay at an energy significantly below the transition state barrier of 19.46 ± 0.25 kcal mol −1 , refined utilizing a high-level electronic structure method HEAT-345(Q) Λ . The observed unimolecular decay rate of 1.6 ± 0.4 × 10 6 s −1 is 2 orders of magnitude slower than that predicted by statistical unimolecular reaction theory using several different models for quantum mechanical tunneling. The nonstatistical behavior originates from excitation of a CH stretch vibration that is orthogonal to the heavy atom motions along the reaction coordinate and slow intramolecular vibrational energy redistribution due to the sparse density of states.

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Factorized Quadruples and a Predictor of Higher-Level Correlation in Thermochemistry

Thorpe,

Windom,

Bartlett

et al. 2024

J. Phys. Chem. A

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Coupled cluster theory has had a momentous impact on the ab initio prediction of molecular properties, and remains a staple ingratiate in high-accuracy thermochemical model chemistries. However, these methods require inclusion of at least some connected quadruple excitations, which generally scale at best as N ( ) 9 with the number of basis functions. It is very difficult to predict, a priori, the effect correlation of past CCSD(T) on a given reaction energy. The purpose of this work is to examine costeffective quadruple corrections based on the factorization theorem of the many-body perturbation theory that may address these challenges. We show that the N ( ) 7 factorized CCSD(TQ f ) method introduces minimal error to predicted correlation and reaction energies as compared to the N ( )9 CCSD(TQ). Further, we examine the performance of Goodson's continued fraction method in the estimation of CCSDT(Q) Λ contributions to reaction energies as well as a "new" method related to %TAE[(T)] that we refer to as a scaled perturbation estimator. We find that the scaled perturbation estimator based upon CCSD(TQ f )/cc-pVDZ is capable of predicting CCSDT(Q) Λ /cc-pVDZ contributions to reaction energies with an average error of 0.07 kcal mol −1 and an L 2 D of 0.52 kcal mol −1 when applied to a test-suite of nearly 3000 reactions. This offers a means by which to reliably "ballpark" how important post-CCSD(T) contributions are to reaction energies while incurring no more than CCSD(T) formal cost and a little mental math.

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W4Λ: Leveraging Λ Coupled-Cluster for Accurate Computational Thermochemistry Approaches

Cited by 3 publications

References 66 publications

Toward Accurate Quantum Chemical Methods for Molecules of Increasing Dimension: The New Family of Pisa Composite Schemes

Toward Accurate Quantum Chemical Methods for Molecules of Increasing Dimension: The New Family of Pisa Composite Schemes

Nonstatistical Unimolecular Decay of the CH₂OO Criegee Intermediate in the Tunneling Regime

Factorized Quadruples and a Predictor of Higher-Level Correlation in Thermochemistry

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W4Λ: Leveraging Λ Coupled-Cluster for Accurate Computational Thermochemistry Approaches

Cited by 3 publications

References 66 publications

Toward Accurate Quantum Chemical Methods for Molecules of Increasing Dimension: The New Family of Pisa Composite Schemes

Toward Accurate Quantum Chemical Methods for Molecules of Increasing Dimension: The New Family of Pisa Composite Schemes

Nonstatistical Unimolecular Decay of the CH2OO Criegee Intermediate in the Tunneling Regime

Factorized Quadruples and a Predictor of Higher-Level Correlation in Thermochemistry

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Nonstatistical Unimolecular Decay of the CH₂OO Criegee Intermediate in the Tunneling Regime