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Title: Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions

Abstract

We extend our assessment of the potential of perturbative coupled cluster (CC) expansions for a test set of open-shell atoms and organic radicals to the description of quadruple excitations. Namely, the second- through sixth-order models of the recently proposed CCSDT(Q–n) quadruples series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)] are compared to the prominent CCSDT(Q) and ΛCCSDT(Q) models. From a comparison of the models in terms of their recovery of total CC singles, doubles, triples, and quadruples (CCSDTQ) energies, we find that the performance of the CCSDT(Q–n) models is independent of the reference used (unrestricted or restricted (open-shell) Hartree-Fock), in contrast to the CCSDT(Q) and ΛCCSDT(Q) models, for which the accuracy is strongly dependent on the spin of the molecular ground state. By further comparing the ability of the models to recover relative CCSDTQ total atomization energies, the discrepancy between them is found to be even more pronounced, stressing how a balanced description of both closed- and open-shell species—as found in the CCSDT(Q–n) models—is indeed of paramount importance if any perturbative CC model is to be of chemical relevance for high-accuracy applications. In particular, the third-order CCSDT(Q–3) model is found to offer an encouraging alternative tomore » the existing choices of quadruples models used in modern computational thermochemistry, since the model is still only of moderate cost, albeit markedly more costly than, e.g., the CCSDT(Q) and ΛCCSDT(Q) models.« less

Authors:
 [1];  [2];  [3]
  1. qLEAP Center for Theoretical Chemistry, Department of Chemistry, Aarhus University, DK-8000 Aarhus C (Denmark)
  2. The Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712 (United States)
  3. Institut für Physikalische Chemie, Johannes Gutenberg-Universität Mainz, D-55128 Mainz (Germany)
Publication Date:
OSTI Identifier:
22658006
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 144; Journal Issue: 19; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACCURACY; COMPUTERIZED SIMULATION; GROUND STATES; HARTREE-FOCK METHOD; PERTURBATION THEORY

Citation Formats

Eriksen, Janus J., E-mail: janusje@chem.au.dk, Jørgensen, Poul, Matthews, Devin A., and Gauss, Jürgen. Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions. United States: N. p., 2016. Web. doi:10.1063/1.4948781.
Eriksen, Janus J., E-mail: janusje@chem.au.dk, Jørgensen, Poul, Matthews, Devin A., & Gauss, Jürgen. Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions. United States. https://doi.org/10.1063/1.4948781
Eriksen, Janus J., E-mail: janusje@chem.au.dk, Jørgensen, Poul, Matthews, Devin A., and Gauss, Jürgen. 2016. "Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions". United States. https://doi.org/10.1063/1.4948781.
@article{osti_22658006,
title = {Assessment of the accuracy of coupled cluster perturbation theory for open-shell systems. II. Quadruples expansions},
author = {Eriksen, Janus J., E-mail: janusje@chem.au.dk and Jørgensen, Poul and Matthews, Devin A. and Gauss, Jürgen},
abstractNote = {We extend our assessment of the potential of perturbative coupled cluster (CC) expansions for a test set of open-shell atoms and organic radicals to the description of quadruple excitations. Namely, the second- through sixth-order models of the recently proposed CCSDT(Q–n) quadruples series [J. J. Eriksen et al., J. Chem. Phys. 140, 064108 (2014)] are compared to the prominent CCSDT(Q) and ΛCCSDT(Q) models. From a comparison of the models in terms of their recovery of total CC singles, doubles, triples, and quadruples (CCSDTQ) energies, we find that the performance of the CCSDT(Q–n) models is independent of the reference used (unrestricted or restricted (open-shell) Hartree-Fock), in contrast to the CCSDT(Q) and ΛCCSDT(Q) models, for which the accuracy is strongly dependent on the spin of the molecular ground state. By further comparing the ability of the models to recover relative CCSDTQ total atomization energies, the discrepancy between them is found to be even more pronounced, stressing how a balanced description of both closed- and open-shell species—as found in the CCSDT(Q–n) models—is indeed of paramount importance if any perturbative CC model is to be of chemical relevance for high-accuracy applications. In particular, the third-order CCSDT(Q–3) model is found to offer an encouraging alternative to the existing choices of quadruples models used in modern computational thermochemistry, since the model is still only of moderate cost, albeit markedly more costly than, e.g., the CCSDT(Q) and ΛCCSDT(Q) models.},
doi = {10.1063/1.4948781},
url = {https://www.osti.gov/biblio/22658006}, journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 19,
volume = 144,
place = {United States},
year = {Sat May 21 00:00:00 EDT 2016},
month = {Sat May 21 00:00:00 EDT 2016}
}