C2V Insertion pathway for BeH2: A test problem for the coupled‐cluster single and double excitation model

Purvis, George D.; Shepard, Ron; Brown, Franklin B.; Bartlett, Rodney J.

doi:10.1002/qua.560230307

Cited by 151 publications

(102 citation statements)

References 33 publications

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“…Potential energy curve for the insertion of a beryllium atom into H 2 (6-311G basis set). 55 A beryllium atom is placed at the origin of the coordinate system, while the positions of the hydrogen atoms are defined as y(x) = ±(2.54 − 0.46x). 56 For CASSCF, CASPT2, and CT-MP2, the (2e, 2o) active space was used.…”

Section: Resultsmentioning

confidence: 99%

A transformed framework for dynamic correlation in multireference problems

Sokolov

Chan

2015

The Journal of Chemical Physics

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We describe how multireference dynamic correlation theories can be naturally obtained as singlereference correlation theories in a canonically transformed frame. Such canonically transformed correlation theories are very simple and involve identical expressions to their single-reference counterparts. The corresponding excitations involve quasiparticles rather than the bare particles of the system. High-order density matrices (or their approximations) and the numerical metric instabilities common to multireference correlation theories do not appear. As an example, we formulate the Bogoliubov canonically transformed version of second-order Møller-Plesset perturbation theory and demonstrate its performance in H 2 , H 2 O, N 2 , and BeH 2 bond dissociation. C 2015 AIP Publishing LLC. [http://dx

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Section: Resultsmentioning

confidence: 99%

A transformed framework for dynamic correlation in multireference problems

Sokolov

Chan

2015

The Journal of Chemical Physics

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“…Following Laidig and Bartlett [29] we have performed the calculations within the same orbital space for three geometries corresponding to Be insertion into H,, which are in the vicinity of the maximum along the C,, constraint reaction path. As was found by Purvis et al [40] far these geometries, the two configurations la:2a:lb: and la:2a:3a: are very important, which justifies a multireference approach.…”

Section: Behmentioning

confidence: 82%

A coupled‐cluster method for quasidegenerate states

Meissner

Jankowski

Wasilewski

1988

Int J of Quantum Chemistry

178

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A size-extensive, multireference coupled-cluster method for studies of quasidegenerate states based on the Jeziorski-Monkhorst [16] ansatz for the cluster operator (a = SeqP,, where the sum is extended over the configurations spanning the model space), is presented and applied in pilot calculations. The method is referred to as multireference coupled electron-pair method (MR CEPM), because it is assumed that the individual cluster operators can be approximated by their two-body parts, i.e., T, == T,(2). The linear version of this method (MR L-CEPM) is also discussed. Both methods are applied to two simple model systems: (1) a minimum basis set model involving eight hydrogen atoms in various spacial arrangements for which the degree of quasidegeneracy can be continuously varied; (2) The usefulness of the cluster ansatz for representing the wave function in the many-fermion theory became apparent from the work of Hubbard [ 11 almost 30 years ago. Since then much work has been invested into the development of size-extensive [2,3] methods of approximately solving the Schrodinger equation which are based on this ansatz. Let us just mention the pioneering work of Coester and Kumme1 [4] in the nuclear many-body problem, followed by that of hick [5] in the many-electron theory of atomic and molecular systems. Extensive reviews of both methodological and computational developments of these methods, known as coupled-cluster (cc) methods, are currently available [6-91. Due to the developments just mentioned, various versions of the cc approach have become broadly used standard ab initio methods for electron correlation studies in many-electron closed-shell states. Unfortunately, the generalization of cc methods to the non-closed-shell case, i.e., to quasidegenerate and open-shell states, turned out to be a very difficult problem. Despite the progress achieved during the present decade, for quasidegenerate states the cc methods are still rather far from becoming a reliable standard tool of contemporary quantum chemistry. Since the cluster ansatz may be considered as a very compact representation of a perturbation expansion, the problems encountered

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“…When the Be is far from the hydrogen molecule, |(1a 1 [32]. An ANO basis set proposed by WidmarkMalmquist-Roos [33] was adopted as valence triple zeta plus double polarization contraction (H: 3s2p, Be: 4s3p2d) using spherical harmonics.…”

Section: The Be/h 2 Systemmentioning

confidence: 99%

Multireference coupled electron-pair approximations to the multireference coupled cluster method. The MR-CEPA1 method

2005

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An extension of the CEPA1 method to the multi-reference case is presented, the MR-CEPA1 approach. The method takes the variationally included terms into account as in MRDCEPA and corrects for the exclusion principle violating terms as in closed shell CEPA1. It is shown that this method yields potential energy curves that are close to those of the multi-reference coupled cluster method and parallel the full CI results quite well. The size consistency of the method is as good as the MRDCEPA method and much better than approaches that ignore the VI terms like MR-ACPF and MR-AQCC. A simpler method, where the EPV terms are not corrected on an individual basis for the doubly occupied orbitals, dubbed the multi-reference averaged CEPA1 method (MR-ACEPA), which is akin to methods previously suggested by Szalay et al., is comparable in performance.

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C_2V Insertion pathway for BeH₂: A test problem for the coupled‐cluster single and double excitation model

Cited by 151 publications

References 33 publications

A transformed framework for dynamic correlation in multireference problems

A transformed framework for dynamic correlation in multireference problems

A coupled‐cluster method for quasidegenerate states

Multireference coupled electron-pair approximations to the multireference coupled cluster method. The MR-CEPA1 method

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