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Coupled cluster

About: Coupled cluster is a research topic. Over the lifetime, 6280 publications have been published within this topic receiving 301055 citations.


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TL;DR: In this article, a coupled cluster procedure using relatively large basis sets and an energyconsistent semilocal three valence electron pseudopotential for indium was used to determine the dipole moment and dipole-polarizability of diatomic InCl.
Abstract: Spectroscopic constants for InCl and InCl3 are determined by a coupled cluster procedure using relatively large basis sets and an energy‐consistent semilocal three valence electron pseudopotential for indium. Possible errors within the pseudopotential approximation are discussed in detail by comparison of available pseudopotentials adjusted through different techniques. Core‐polarization corrections and the deviation from a point core approximation are discussed. These corrections, however, do not lead to more accurate bond distances as compared to the experimental results. Differently adjusted three valence electron pseudopotentials yield quite different results for the bond distances of InCl and InCl3. The single‐electron adjusted energy‐consistent pseudopotential of Igel‐Mann et al. [Mol. Phys. 65, 1321 (1988)] yields the best results and therefore, this pseudopotential has been chosen for all further investigations on molecular properties. The Dunham parameters for InCl are calculated by solving the vibrational‐rotational Schrodinger equation numerically. A finite field technique is used to determine the dipole moment and dipole‐polarizability of diatomic InCl. The dependence of several molecular properties on the vibrational quantum state is determined by calculating the expectation value Pn=〈n‖P(R)‖n〉, where P(R) is the distance dependent molecular property. The P(R) curves show strong linear behavior and therefore, the shape of the Pn curve is mostly determined by anharmonicity effects in the InCl potential curve. For the vibrational ground state, ‖0〉, the calculated property P0 deviates only slightly from the property determined directly at the equilibrium distance, Pe. There is in general satisfying agreement of our calculated values with available experimental results. However, it is concluded that in order to obtain very accurate spectroscopic constants a small core definition for indium has to be preferred.

72 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a systematic derivation of the multireference coupled cluster theory based on the single reference formalism, which is essential for the correct theoretical determination of dissociation energies as well as other molecular properties.
Abstract: In this review we present a systematic derivation of the multireference coupled cluster theory based on the single reference formalism. The coupled cluster theories have recently emerged as one of the major method development activities in the electronic structure theory of atoms and molecules. Due to its size-extensive nature, using the coupled cluster method the total electronic energy of the system can be determined with the same relative accuracy as the total electronic energies of the fragments which the system separates into in the process of chemical decomposition. This feature is essential for the correct theoretical determination of dissociation energies as well as other molecular properties. One of the most difficult challenges in advancing the coupled cluster theory has been the development of the multireference coupled cluster methodology, i.e. generating a scheme which allows the reference function to incorporate more than one Slater determinant. Such development would enable a very ...

72 citations

Journal ArticleDOI
05 Jun 2012
TL;DR: In this article, the authors proposed a flexible MMCC (Flex-MMCC) formalism to correct the results of the CC calculations with singles, doubles, and active-space triples for the remaining effects due to connected triple excitations that are missing in the CCSDt considerations.
Abstract: After reviewing recent progress in the area of the development of coupled-cluster (CC) methods for quasi-degenerate electronic states that are characterized by stronger non-dynamical correlation effects, including new generations of single- and multi-reference approaches that can handle bond breaking and excited states dominated by many-electron transitions, and after discussing the key elements of the left-eigenstate completely renormalized (CR) CC and equation-of-motion (EOM) CC methods, and the underlying biorthogonal method of moments of CC (MMCC) equations [P. Piecuch, M. Wloch, J. Chem. Phys. 123 (2005) 224105; P. Piecuch, M. Wloch, J.R. Gour, A. Kinal, Chem. Phys. Lett. 418 (2006) 467; M. Wloch, M.D. Lodriguito, P. Piecuch, J.R. Gour, Mol. Phys. 104 (2006) 2149], it is argued that it is beneficial to merge the CR-CC/EOMCC and active-space CC/EOMCC [P. Piecuch, Mol. Phys. 108 (2010) 2987, and references therein] theories into a single formalism. In order to accomplish this goal, the biorthogonal MMCC theory, which provides compact many-body expansions for the differences between the full configuration interaction and CC or, in the case of excited states, EOMCC energies, obtained using conventional truncation schemes in the cluster operator T and excitation operator Rμ, is generalized, so that one can correct the CC/EOMCC energies obtained with arbitrary truncations in T and Rμ for the selected many-electron correlation effects of interest. The resulting moment expansions, defining the new, Flexible MMCC (Flex-MMCC) formalism, and the ensuing CC(P; Q) hierarchy, proposed in the present work, enable one to correct energies obtained in the active-space CC and EOMCC calculations, in which one selects higher many-body components of T and Rμ via active orbitals and which recover much of the relevant non-dynamical and some dynamical electron correlation effects in applications involving potential energy surfaces (PESs) along bond breaking coordinates, for the effects of higher-order, primarily dynamical, correlations missing in the active-space CC/EOMCC considerations. The Flex-MMCC corrections to the active-space CC/EOMCC energies are mathematically similar to the non-iterative energy corrections defining the existing left-eigenstate CR-CC and CR-EOMCC methods, such as CR-CC(2, 3) and CR-EOMCC(2, 3). The potential advantages of the Flex-MMCC and CC(P; Q) formalisms are illustrated by describing the initial implementation and numerical tests of the novel CC hybrid scheme, abbreviated as CC(t; 3), in which one corrects the results of the CC calculations with singles, doubles, and active-space triples, termed CCSDt, for the remaining effects due to connected triple excitations that are missing in the CCSDt considerations, but are present in the MMCC-based CR-CC(2, 3) approach. By examining bond breaking in the HF, F2, and F 2 + molecules, it is demonstrated that the CC(t; 3) method improves the CCSDt and CR-CC(2, 3) results, providing PESs that agree with those obtained with the full CC theory with singles, doubles, and triples (CCSDT) to within small fractions of a millihartree, at the fraction of the computer costs of the CCSDT calculations. Different strategies for defining active-space triples within the CC(t; 3) scheme and the underlying CCSDt method are discussed. When limited to the ground-state problem, the CC(t; 3) approach can be regarded as an improved and rigorously derived extension of the recently proposed CCSD(T)-h method [J. Shen, E. Xu, Z. Kou, S. Li, J. Chem. Phys. 132 (2010) 114115], in which triples corrections of the CCSD(T) type are replaced by their more robust CR-CC(2, 3)-style analogs.

72 citations

Journal ArticleDOI
TL;DR: In this paper, high-accuracy calculations of atomic properties of the superheavy elements up to element 122 are reviewed, including ionization potentials, electron affinities and excitation energies.

71 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigate how different DFT functionals (M06-2X, PW91, ω B97X-D) and basis sets affect the thermal contribution to the Gibbs free energy and single point energy.

71 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023163
2022351
2021267
2020344
2019253
2018244