Singlet-paired coupled cluster theory for open shells

Journal Article · Tue Jun 28 04:00:00 EDT 2016 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4954891· OSTI ID:22675979

Gomez, John A. ^[1]; Henderson, Thomas M.; Scuseria, Gustavo E. ^[1]

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1. Department of Chemistry, Rice University, Houston, Texas 77005 (United States)

Restricted single-reference coupled cluster theory truncated to single and double excitations accurately describes weakly correlated systems, but often breaks down in the presence of static or strong correlation. Good coupled cluster energies in the presence of degeneracies can be obtained by using a symmetry-broken reference, such as unrestricted Hartree-Fock, but at the cost of good quantum numbers. A large body of work has shown that modifying the coupled cluster ansatz allows for the treatment of strong correlation within a single-reference, symmetry-adapted framework. The recently introduced singlet-paired coupled cluster doubles (CCD0) method is one such model, which recovers correct behavior for strong correlation without requiring symmetry breaking in the reference. Here, we extend singlet-paired coupled cluster for application to open shells via restricted open-shell singlet-paired coupled cluster singles and doubles (ROCCSD0). The ROCCSD0 approach retains the benefits of standard coupled cluster theory and recovers correct behavior for strongly correlated, open-shell systems using a spin-preserving ROHF reference.

• OSTI ID: 22675979
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 24 Vol. 144; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
COMPUTER CALCULATIONS
CORRELATIONS
HARTREE-FOCK METHOD
QUANTUM NUMBERS
SYMMETRY BREAKING