The averaged coupled-pair functional (ACPF): A size-extensive modification of MR CI(SD)

Gdanitz, Robert J.; Ahlrichs, Reinhart

doi:10.1016/0009-2614(88)87388-3

Cited by 868 publications

(469 citation statements)

References 30 publications

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“…26 This was done both because it is desirable to use a size-extensive method when a large numbers of electrons are correlated and because it is preferred to use a multireference method when describing a bond breaking process. The core-electron correlation energies were calculated employing a series of correlationconsistent polarized core-valence n-basis sets 25 (cc-pCVnZ or CVnZ for n ) 3, 4, and 5) and extrapolated to the complete basis set limit using the extrapolation method described above.…”

Section: Methodsmentioning

confidence: 99%

Spectroscopic Properties of MgH₂, MgD₂, and MgHD Calculated from a New ab Initio Potential Energy Surface

Roy

2007

J. Phys. Chem. A

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A three-dimensional potential energy surface for the ground electronic state of MgH 2 has been constructed from 9030 symmetry-unique ab initio points calculated using the icMRCI+Q method with aug-cc-pVnZ basis sets for n ) 3, 4, and 5, with core-electron correlation calculated at the MR-ACPF level of theory using cc-pCVnZ basis sets, with both calculations being extrapolated to the complete basis set limit. Calculated spectroscopic constants of MgH 2 and MgD 2 are in excellent agreement with recent experimental results: for four bands of MgH 2 and one band of MgD 2 the root-mean-square (rms) band origin discrepancies were only 0.44 and 0.06 cm -1 , respectively, and the rms relative discrepancies in the inertial rotational constants (B [V] ) were only 0.0196% and 0.0058%, respectively. Spectroscopic constants for MgHD were predicted using the same potential surface.

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Section: Methodsmentioning

confidence: 99%

Spectroscopic Properties of MgH₂, MgD₂, and MgHD Calculated from a New ab Initio Potential Energy Surface

Roy

2007

J. Phys. Chem. A

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“…54 By partitioning the system into n e /2 noninteracting electron pairs (n e is the number of correlated electrons), the average of the pair energies becomes…”

Section: B Pair-energy and Several Approximationsmentioning

confidence: 99%

“…(20). 54 Meissner suggested a different averaging by considering the actual number of pairs, ne 2 . 24 The averaged pair-energy in this case becomes…”

Section: B Pair-energy and Several Approximationsmentioning

confidence: 99%

Bridging Single- and Multireference Domains for Electron Correlation: Spin-Extended Coupled Electron Pair Approximation

Tsuchimochi

Ten‐no

2017

J. Chem. Theory Comput.

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We propose a size-consistent generalization of the recently developed spin-extended configuration interaction with singles and doubles (ECISD), where a CI wave function is explicitly spin-projected. The size-consistent effect is effectively incorporated by treating quadruples within the formulation of coupled electron pair approximation. As in coupled-cluster theory, quadruple excitations are approximated by a disconnected product of double excitations. Despite its conceptual similarity to the standard single-and multireference analogues, such a generalization requires careful derivation, as the spin-projected CI space is non-orthogonal and overcomplete. Although our methods generally yield better results than ECISD, size-consistency is only approximately retained because the action of a symmetry-projection operator is size-inconsistent. In this work, we focus on simple models where exclusion-principle-violating terms, which eliminate undesired contributions to the correlation effects, are either completely neglected or averaged. These models possess an orbital-invariant energy functional that is to be minimized by diagonalizing an energy-shifted effective Hamiltonian within the singles and doubles manifold. This allows for a straightforward generalization of the ECISD analytical gradients needed to determine molecular properties and geometric optimization. Given the multireference nature of the spin-projected Hartree-Fock method, the proposed approaches are expected to handle static correlation, unlike single-reference analogues. We critically assess the performance of our methods using dissociation curves of molecules, singlet-triplet splitting gaps, hyperfine coupling constants, and the chromium dimer. The size-consistency and size-extensivity of the methods are also discussed.

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“…The initial publication covers the elements HAAr, [33] with the multireference averaged coupled-pair functional method used in the optimization. [34] A number of variations in polarization functions and contractions were benchmarked in terms of HF energy, correlation energy, and total energy, before comparison with several basis sets from other families. Although the initial results with these ano-pVnZ (n ¼ D, T, Q) bases appear promising, at the time of writing, it is unclear how well the basis sets perform for atomic/molecular properties and for relative energies.…”

Section: Atomic Natural Orbital Basis Setsmentioning

confidence: 99%

Gaussian basis sets for molecular applications

Hill¹

2012

Int J of Quantum Chemistry

188

155

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The choice of basis set in quantum chemical calculations can have a huge impact on the quality of the results, especially for correlated ab initio methods. This article provides an overview of the development of Gaussian basis sets for molecular calculations, with a focus on four popular families of modern atom-centered, energy-optimized bases: atomic natural orbital, correlation consistent, polarization consistent, and def2. The terminology used for describing basis sets is briefly covered, along with an overview of the auxiliary basis sets used in a number of integral approximation techniques and an outlook on possible future directions of basis set design.

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The averaged coupled-pair functional (ACPF): A size-extensive modification of MR CI(SD)

Cited by 868 publications

References 30 publications

Spectroscopic Properties of MgH₂, MgD₂, and MgHD Calculated from a New ab Initio Potential Energy Surface

Spectroscopic Properties of MgH₂, MgD₂, and MgHD Calculated from a New ab Initio Potential Energy Surface

Bridging Single- and Multireference Domains for Electron Correlation: Spin-Extended Coupled Electron Pair Approximation

Gaussian basis sets for molecular applications

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The averaged coupled-pair functional (ACPF): A size-extensive modification of MR CI(SD)

Cited by 868 publications

References 30 publications

Spectroscopic Properties of MgH2, MgD2, and MgHD Calculated from a New ab Initio Potential Energy Surface

Spectroscopic Properties of MgH2, MgD2, and MgHD Calculated from a New ab Initio Potential Energy Surface

Bridging Single- and Multireference Domains for Electron Correlation: Spin-Extended Coupled Electron Pair Approximation

Gaussian basis sets for molecular applications

Contact Info

Product

Resources

About

Spectroscopic Properties of MgH₂, MgD₂, and MgHD Calculated from a New ab Initio Potential Energy Surface

Spectroscopic Properties of MgH₂, MgD₂, and MgHD Calculated from a New ab Initio Potential Energy Surface