期刊
JOURNAL OF CHEMICAL PHYSICS
卷 132, 期 7, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.3305335
关键词
coupled cluster calculations; perturbation theory; potential energy surfaces; wave functions
资金
- Deutsche Forschungsgemeinschaft
- Fonds der Chemischen Industrie
- U.S. National Science Foundation [CHE-0749868]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [749868] Funding Source: National Science Foundation
We formulated and implemented a perturbative triples correction for the state-specific multireference coupled cluster approach with singles and doubles suggested by Mukherjee and co-workers, Mk-MRCCSD [Mol. Phys. 94, 157 (1998)]. Our derivation of the energy correction [Mk-MRCCSD(T)] is based on a constrained search for stationary points of the Mk-MRCC energy functional together with a perturbative expansion with respect to the appearing triples cluster operator. The Lambda-Mk-MRCCSD(T) approach derived in this way consists in (1) a correction to the off-diagonal matrix elements of the effective Hamiltonian which is unique to coupled cluster methods based on the Jeziorski-Monkhorst ansatz, and (2) an asymmetric energy correction to the diagonal elements of the effective Hamiltonian. The Mk-MRCCSD(T) correction is obtained from the Lambda-Mk-MRCCSD(T) method by approximating the singles and doubles Lagrange multipliers with the corresponding cluster amplitudes. We investigate the performance of the Mk-MRCCSD(T) method by applying it to the potential energy curve of the BeH2 model and F-2 and the geometry and harmonic vibrational frequencies of ozone. Computation of the energy difference between the mono- and bicyclic forms of the 2,6-pyridyne diradical illustrates the potential of Mk-MRCCSD(T) as a tool for the study of realistic chemical problems requiring multireference zeroth-order wave functions.
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