title: Communication: The performance of non-iterative coupled cluster quadruples models.
abstract: We compare the numerical performance of various non-iterative coupled cluster (CC) quadruples models. The results collectively show how approaches that attempt to correct the CC singles and doubles energy for the combined effect of triple and quadruple excitations all fail at recovering the correlation energy of the full CC singles, doubles, triples, and quadruples (CCSDTQ) model to within sufficient accuracy. Such a level of accuracy is only achieved by models that make corrections to the full CC singles, doubles, and triples (CCSDT) energy for the isolated effect of quadruple excitations of which the CCSDT(Q-3) and CCSDT(Q-4) models of the Lagrangian-based CCSDT(Q-n) perturbation series are found to outperform alternative models that add either of the established [Q] and (Q) corrections to the CCSDT energy.
authors.affiliation: Department of Chemistry, qLEAP Center for Theoretical Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark.
authors.forename: Janus J
authors.initials: JJ
authors.lastname: Eriksen
authors.affiliation: The Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Devin A
authors.initials: DA
authors.lastname: Matthews
authors.affiliation: Department of Chemistry, qLEAP Center for Theoretical Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark.
authors.forename: Poul
authors.initials: P
authors.lastname: Jørgensen
authors.affiliation: Institut für Physikalische Chemie, Johannes Gutenberg-Universität Mainz, D-55128 Mainz, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Gauss