Active-space coupled-cluster methods through connected quadruple excitations

Peng Dong Fan, So Hirata

Research output: Contribution to journalArticlepeer-review


Coupled-cluster methods that include just a subset of all connected triple, quadruple, or both excitation amplitudes, according to the ansatz of and Adamowicz co-workers [Int. Rev. Phys. Chem. 12, 339 (1993); J. Chem. Phys. 99, 1875 (1993); 100, 5792 (1994)] and Piecuch [J. Chem. Phys. 110, 6103 (1999)], have been implemented into parallel execution programs. They are applicable to closed- and open-shell species and they take advantage of real Abelian point-group symmetry. A symbol manipulation program has been invoked to automate the implementation. These methods have been applied to the singlet-triplet separations of five triatomic hydrides (C H2, N H2+, Si H2, P H2+, and As H2+) with consideration of scalar relativistic effects. They have been shown to be remarkably effective with errors arising from the use of a very small subset of higher-order excitations being no more than a few tenths of 1 kcalmol.

Original languageEnglish (US)
Article number104108
JournalJournal of Chemical Physics
Issue number10
StatePublished - 2006
Externally publishedYes

ASJC Scopus subject areas

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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