An efficient and accurate approximation to double substitution coupled cluster wavefunctions

Chiles, Richard A.; Dykstra, Clifford E.

doi:10.1016/0009-2614(81)80059-0

Cited by 144 publications

(39 citation statements)

References 16 publications

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“…Thi~ m~thgg iii! RJlJl<:1g gO fin ~xp.gmmtifil ~Xpfimlign of the wave operator acting on the reference determinant, 10), to produce the coupled-cluster wavefunctionj (21) Where the exponential operator is expanded as; (22) and the T operator is; (23) In the language of second quantization the cluster operators are;…”

mentioning

confidence: 99%

Multireference coupled-cluster method using a single-reference formalism

Oliphant

Adamowicz²

1991

The Journal of Chemical Physics

320

175

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A multireference coupled-cluster singles and doubles method utilizing two reference determinants which differ by a two electron excitation is proposed. One of these determinants is selected as the formal reference determinant. The proposed method includes single-reference coupled-cluster equations truncated after quadruples. These equations are graphically derived using Feynman diagrams. The appropriate restrictions are then placed on the triple and quadruple amplitudes to allow only those amplitudes which correspond to single and double excitations from the second reference determinant.

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mentioning

confidence: 99%

Multireference coupled-cluster method using a single-reference formalism

Oliphant

Adamowicz²

1991

The Journal of Chemical Physics

320

175

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“…It is also simpler to implement than full CCD [14]. The results of the calculations here and our results for comparisons of ACCD and CCD presented earlier [14,26] show that ACCD consistently yields energies that are only slightly different from the CCD energies (Table II). More significant, ACCD potential curves and potential surface slices are very close to CCD curves.…”

Section: Resultsmentioning

confidence: 49%

“…The CID/cr correlation energy is the CID correlation energy multiplied by ψ CID |ψ CID (intermediate normalization of ψ CID ). Another treatment that scales in cost like CID was used for most of the systems and it is an approximation to CCD, which we designated ACCD [14] and which was first developed in a different way and designated ACP-D45 by Jankowski and Paldus [15]. All the treatments are those built with double-substitution operators acting on a single configuration reference, and the most complete of these treatments, CCD, provides the basis for comparison.…”

Section: Resultsmentioning

confidence: 99%

“…Coupled cluster double substitution scales no worse than CID with N and K [11 -13]; however, the constants that multiply the various NK terms in a detailed analysis of the computational steps make CCD more costly than CID. There is an approximate form [14,15] of CCD that is very close to CID in computational cost, and comparisons are made with that approach in the calculations reported here. Even so, MP2 stands out sharply in computational cost: It is a big step to any higher level of treatment involving the same configurational space.…”

Section: Theorymentioning

confidence: 97%

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Enhanced second-order treatment of electron pair correlation

Dykstra

Davidson

2000

Int. J. Quantum Chem.

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Ab initio calculations have been performed for F 2 , HCCH, H 2 O, HF, (HF) 2 , and (H 2 O) 2 , comparing certain electron pair correlation methods, or methods for doubly substituted configurations. In these model systems, the reweighting of substituted configurations that occurs beyond a second-order perturbative treatment of electron correlation can be partly built into the second-order analysis in a computationally trivial step. Specific means for doing this are explored, and they offer improvement in certain cases or else very little change. A consistent improvement in the correlation energy when judged against treatment with double substitution coupled cluster theory for the test species is obtained through one of these schemes.

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“…(2.93b), cancels certain nonlinear terms of the standard CCD theory (namely, the diagrams of the type shown in Figure 8(ii) (h) and ('j 1, j2) that are separable over one or two hole lines and that produce important EPV terms). In this case, the CCDQ' method reduces to the so-called approximate coupled pair (ACP) or approximate CCD (ACCD) approach, each of which has been independently put forward earlier [190,196,207,209,234]. The precise account of this cancellation led to the so-called approximate-coupled-pair-theory-with-quadruples (ACPQ) method (which differs from ACCD by a numerical factor of 9 multiplying the contributions from diagram (h) of Figure 8(ii) for triplet-coupled pp-hh t2-amplitudes [208]).…”

Section: 3mentioning

confidence: 99%