Size-consistent Brillouin-Wigner perturbation theory with an exponentially parametrized wave function: Brillouin-Wigner coupled-cluster theory

Hubač, Ivan; Neogrády, Pavel

doi:10.1103/physreva.50.4558

Cited by 80 publications

(53 citation statements)

References 17 publications

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“…To avoid the intruder states, the SS-MRCC approach [87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103], which treats one state at a time with a state-specific wave operator, has been developed. Existing SS-MRCC methods include, for example, Mk-CCSD [78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95], single-root MR BWCCSD [96][97][98][99][100][101], and MRexpT [102,103]. These methods have been shown to give quite accurate descriptions for electronic structures of molecules with strong multireference character.…”

Section: Introductionmentioning

confidence: 99%

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Fang

2010

Challenges and Advances in Computational Chemistry and Physics

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Abstract:We have presented in this chapter the general formalism of block correlated coupled cluster method with a CASSCF reference function (CAS-BCCC in short) and a number of its applications for electronic structure calculations of molecules with multireference character. The CAS-BCCC method has the following features: (1) free of the intruder states; (2) invariant with respect to orbital rotations within separated orbital subspaces (occupied, active, and virtual); (3) cost-effective; (4) core-extensive, but not size-extensive with respect to the total number of electrons. With the cluster operator truncated up to the four-block correlation level, the approximate CAS-BCCC method is named as CAS-BCCC4. The CAS-BCCC4 method is applied to investigate a number of chemical problems such as bond breaking potential energy surfaces, singlet-triplet gaps of diradicals, reaction barriers, spectroscopic constants of diatomic molecules, and low-lying excited states. Comparisons between results from CAS-BCCC4 and those from FCI or other theoretical methods demonstrate that the CAS-BCCC4 approach provides very accurate descriptions for all problems under study. The overall performance of CAS-BCCC4 is illustrated to be better than that of CASPT2 and MR-CISD methods.

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Section: Introductionmentioning

confidence: 99%

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Fang

2010

Challenges and Advances in Computational Chemistry and Physics

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“…Following Ref 19,. The third possible approach relies on the Brillouin-Wigner ͑BW͒ form of MR CC equations[61][62][63][64][65][66][67][68] This approach was recently implemented in general purpose codes by Evangelista et al59,60 and applied to a number of systems, including diradicaloid species.…”

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confidence: 99%

Electronic structure of organic diradicals: Evaluation of the performance of coupled-cluster methods

Paldus

2008

The Journal of Chemical Physics

106

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The performance of (i) the reduced multireference (RMR) coupled-cluster (CC) method with singles and doubles (RMR CCSD) that employs a modest-size MR CISD wave function as an external source for the most important (primary) triples and quadruples in order to account for the nondynamic correlation effects in the presence of quasidegeneracy, (ii) the RMR CCSD(T) method that adds a perturbative correction for the remaining (secondary) triples to the RMR CCSD energy, and (iii) the recently developed partially linearized MR CCSD method, which determines primary triples and quadruples using a subset of linear CC equations projected onto the corresponding higher-than-doubly excited configurations, are tested by considering the singlet-triplet splitting for several diradicals, ranging from a prototypical methylene radical to trimethylenemethane, and benzyne and pyridynium cation isomers. Both RHF and multiconfigurational self-consistent field molecular orbitals are employed. The equilibrium geometries for the lowest-lying singlet and triplet states are determined using both the density functional theory (DFT) and various CC approaches, and a comparison with both the experiment and other theoretical results, wherever available, is made. The RMR CCSD(T) results provide the most satisfactory description in all cases. The dependence of the MR diradical character on a spatial separation of radical centers, as well as the artifactual DFT geometry in the case of benzyne and pyridynium meta-isomers, is also pointed out.

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“…Now, setting X = ki yields the Brillouin-Wigner (BW) PT, while the choice X = ni gives the Rayleigh-Schrodinger (RS) PT that is the basis of the MBPT. While the BWPT does not give-size extensive energies (when applied to the case K = H , see, however, [183][184][185][186]), the RSPT energy contributions can be arranged into size-extensive terms when grouped by their order in W. Thus, designating the nth-order contributions by the superscript (n) (and dropping the subscript i for simplicity), we write and substitute into Eq. (2.27b).…”

Section: B Many-body Perturbation Theory (Mbpt)mentioning

confidence: 99%

A Critical Assessment of Coupled Cluster Method in Quantum Chemistry

Paldus

1999

Advances in Chemical Physics

336

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Size-consistent Brillouin-Wigner perturbation theory with an exponentially parametrized wave function: Brillouin-Wigner coupled-cluster theory

Cited by 80 publications

References 17 publications

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Electronic structure of organic diradicals: Evaluation of the performance of coupled-cluster methods

A Critical Assessment of Coupled Cluster Method in Quantum Chemistry

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