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Keywords = Method of moments of coupled-cluster equations

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34 pages, 247 KB  
Article
The State-Universal Multi-Reference Coupled-Cluster Theory: An Overview of Some Recent Advances
by Piotr Piecuch and Karol Kowalski
Int. J. Mol. Sci. 2002, 3(6), 676-709; https://doi.org/10.3390/i3060676 - 30 Jun 2002
Cited by 64 | Viewed by 9720
Abstract
Some recent advances in the area of multi-reference coupled-cluster theory of the state-universal type are overviewed. An emphasis is placed on the following new developments: (i) the idea of combining the state-universal multi-reference coupled-cluster singles and doubles method (SUMRCCSD) with the multi-reference many-body [...] Read more.
Some recent advances in the area of multi-reference coupled-cluster theory of the state-universal type are overviewed. An emphasis is placed on the following new developments: (i) the idea of combining the state-universal multi-reference coupled-cluster singles and doubles method (SUMRCCSD) with the multi-reference many-body perturbation theory (MRMBPT), in which cluster amplitudes of the SUMRCCSD formalism that carry only core and virtual orbital indices are replaced by their first-order MRMBPT estimates; and (ii) the idea of combining the recently proposed method of moments of coupled-cluster equations with the SUMRCC formalism. It is demonstrated that the new SUMRCCSD(1) method, obtained by approximating the SUMRCCSD cluster amplitudes carrying only core and virtual orbital indices by their first-order MRMBPT values, provides the results that are comparable to those obtained with the complete SUMRCCSD approach. Full article
(This article belongs to the Special Issue Multireference Quantum Chemical Methods)
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23 pages, 153 KB  
Article
Method of Moments of Coupled-Cluster Equations: Externally Corrected Approaches Employing Configuration Interaction Wave Functions
by Piotr Piecuch, Karol Kowalski and Ian S.O. Pimienta
Int. J. Mol. Sci. 2002, 3(5), 475-497; https://doi.org/10.3390/i3050475 - 31 May 2002
Cited by 28 | Viewed by 8992
Abstract
A new approach to the many-electron correlation problem, termed the method of moments of coupled-cluster equations (MMCC), is further developed and tested. The main idea of the MMCC theory is that of the noniterative energy corrections which, when added to the energies obtained [...] Read more.
A new approach to the many-electron correlation problem, termed the method of moments of coupled-cluster equations (MMCC), is further developed and tested. The main idea of the MMCC theory is that of the noniterative energy corrections which, when added to the energies obtained in the standard coupled-cluster calculations, recover the exact (full configuration interaction) energy. The MMCC approximations require that a guess is provided for the electronic wave function of interest. The idea of using simple estimates of the wave function, provided by the inexpensive configuration interaction (CI) methods employing small sets of active orbitals to define higher–than–double excitations, is tested in this work. The CI-corrected MMCC methods are used to study the single bond breaking in HF and the simultaneous breaking of both O–H bonds in H2O. Full article
(This article belongs to the Special Issue Recent Advances in Coupled Cluster Theory)
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