Seniority zero pair coupled cluster doubles theory

Tamar Stein, Thomas M. Henderson, Gustavo E. Scuseria

Research output: Contribution to journalArticlepeer-review

144 Scopus citations

Abstract

Coupled cluster theory with single and double excitations accurately describes weak electron correlation but is known to fail in cases of strong static correlation. Fascinatingly, however, pair coupled cluster doubles (p-CCD), a simplified version of the theory limited to pair excitations that preserve the seniority of the reference determinant (i.e., the number of unpaired electrons), has mean field computational cost and is an excellent approximation to the full configuration interaction (FCI) of the paired space provided that the orbital basis defining the pairing scheme is adequately optimized. In previous work, we have shown that optimization of the pairing scheme in the seniority zero FCI leads to a very accurate description of static correlation. The same conclusion extends to p-CCD if the orbitals are optimized to make the p-CCD energy stationary. We here demonstrate these results with numerous examples. We also explore the contributions of different seniority sectors to the coupled cluster doubles (CCD) correlation energy using different orbital bases. We consider both Hartree-Fock and Brueckner orbitals, and the role of orbital localization. We show how one can pair the orbitals so that the role of the Brueckner orbitals at the CCD level is retained at the p-CCD level. Moreover, we explore ways of extending CCD to accurately describe strongly correlated systems.

Original languageAmerican English
Article number214113
JournalJournal of Chemical Physics
Volume140
Issue number21
DOIs
StatePublished - 7 Jun 2014
Externally publishedYes

Fingerprint

Dive into the research topics of 'Seniority zero pair coupled cluster doubles theory'. Together they form a unique fingerprint.

Cite this