Second- and third-order triples and quadruples corrections to coupled-cluster singles and doubles in the ground and excited states

Toru Shiozaki, Kimihiko Hirao, So Hirata*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

Second- and third-order perturbation corrections to equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) incorporating excited configurations in the space of triples [EOM-CCSD (2)T and (3)T] or in the space of triples and quadruples [EOM-CCSD (2)TQ] have been implemented. Their ground-state counterparts-third-order corrections to coupled-cluster singles and doubles (CCSD) in the space of triples [CCSD (3)T] or in the space of triples and quadruples [CCSD (3)TQ] -have also been implemented and assessed. It has been shown that a straightforward application of the Rayleigh-Schrödinger perturbation theory leads to perturbation corrections to total energies of excited states that lack the correct size dependence. Approximations have been introduced to the perturbation corrections to arrive at EOM-CCSD (2)T, (3)T, and (2)TQ that provide size-intensive excitation energies at a noniterative O (n7), O (n8), and O (n9) cost (n is the number of orbitals) and CCSD (3)T and (3)TQ size-extensive total energies at a noniterative O (n8) and O (n10) cost. All the implementations are parallel executable, applicable to open and closed shells, and take into account spin and real Abelian point-group symmetries. For excited states, they form a systematically more accurate series, CCSD<CCSD (2)T <CCSD (2)TQ <CCSD (3)T <CCSDT, with the second- and third-order corrections capturing typically ∼80% and 100% of such effects, when those effects are large (>1 eV) and the ground-state wave function has single-determinant character. In other cases, however, the corrections tend to overestimate the triples and quadruples effects, the origin of which is discussed. For ground states, the third-order corrections lead to a rather small improvement over the highly effective second-order corrections [CCSD (2)T and (2)TQ], which is a manifestation of the staircase convergence of perturbation series.

Original languageEnglish (US)
Article number244106
JournalJournal of Chemical Physics
Volume126
Issue number24
DOIs
StatePublished - Aug 2 2007

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Fingerprint Dive into the research topics of 'Second- and third-order triples and quadruples corrections to coupled-cluster singles and doubles in the ground and excited states'. Together they form a unique fingerprint.

Cite this