CASCCD: Coupled-cluster method with double excitations and the CAS reference

Ivanov, V. V.; Adamowicz, Ludwik

doi:10.1063/1.481547

Cited by 75 publications

(46 citation statements)

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“…Another type of MR CC approach (called as CASCCSD) proposed by Adamowicz and his co-workers [116][117][118][119][120][121][122] employs the following exponential ansatz for the wave function,…”

Section: Introductionmentioning

confidence: 99%

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Fang

2010

Challenges and Advances in Computational Chemistry and Physics

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Abstract:We have presented in this chapter the general formalism of block correlated coupled cluster method with a CASSCF reference function (CAS-BCCC in short) and a number of its applications for electronic structure calculations of molecules with multireference character. The CAS-BCCC method has the following features: (1) free of the intruder states; (2) invariant with respect to orbital rotations within separated orbital subspaces (occupied, active, and virtual); (3) cost-effective; (4) core-extensive, but not size-extensive with respect to the total number of electrons. With the cluster operator truncated up to the four-block correlation level, the approximate CAS-BCCC method is named as CAS-BCCC4. The CAS-BCCC4 method is applied to investigate a number of chemical problems such as bond breaking potential energy surfaces, singlet-triplet gaps of diradicals, reaction barriers, spectroscopic constants of diatomic molecules, and low-lying excited states. Comparisons between results from CAS-BCCC4 and those from FCI or other theoretical methods demonstrate that the CAS-BCCC4 approach provides very accurate descriptions for all problems under study. The overall performance of CAS-BCCC4 is illustrated to be better than that of CASPT2 and MR-CISD methods.

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Section: Introductionmentioning

confidence: 99%

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Fang

2010

Challenges and Advances in Computational Chemistry and Physics

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“…[1][2][3][4][5][6] Just to mention a few examples of recently developed methods, and limiting our scope to the restricted field of the statespecific multireference coupled cluster ͑SS-MRCC͒ and closely related approaches, one can quote the SS-BW-MRCC method ͑state-specific Brillouin-Wigner multireference coupled cluster͒, 5,7,8 the SS-MR-CEPA ͑state-specific multireference coupled-electron-pair-approximation͒, 9 the SS-MR-CC method of Mukherjee and co-workers that works on a CAS ͑complete active space͒ 10,11 as well as it does the so-called contracted and uncontracted CASCC methods. 12,13 To make available highly accurate benchmark calculations concerning less-conventional molecular systems is of great convenience for the test of accurate methods, whatever its theoretical foundations be. Such benchmark values can be provided by full CI calculations extended to complete dissociation curves, and extended to some properties closely related to the shape of the potential energy surfaces.…”

Section: Introductionmentioning

confidence: 99%

Full configuration interaction calculation of Be3

Junquera‐Hernández

Sánchez‐Marín

Bendazzoli

et al. 2004

The Journal of Chemical Physics

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The full configuration interaction (FCI) study of the ground state of the neutral beryllium trimer has been performed using an atomic natural orbitals [3s2p1d] basis set. Both triangular and linear structures have been considered for the Be(3) cluster. The optimal geometry for the equilateral triangle has been calculated. The potential energy cut sections along the normal a(1)(') mode and one of the components of the e(') mode have then been studied. The FCI symmetric atomization potential of the linear cluster is also reported. It shows a secondary van der Waals minimum at a long bond distance. All singular points in the potential energy curves are characterized. Other properties, like dissociation energies D(e) and vibrational frequencies, have been estimated from a fourth-order fitting of a large range of points around the minima. The calculated FCI wave number values for the nu(1) and nu(2) normal modes are (467.33+/-0.43) cm(-1) and (390.77+/-0.56) cm(-1).

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“…Our work on the MRCC approach has resulted in development of several distinct methods, which we called CASCCD [16,17] and CAS(n,m)CCSD [18]. They have been derived from the approaches proposed in the earlier works of Oliphant and Adamowicz [13] and Piecuch and co-workers [19,20].…”

Section: Introductionmentioning

confidence: 98%

State-specific multireference complete-active-space coupled-cluster approach versus other quantum chemical methods: dissociation of the N₂molecule

2007

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To cite this article: Dmitry I. Lyakh , Vladimir V. Ivanov & Ludwik Adamowicz (2007) State-specific multireference complete-active-space coupled-cluster approach versus other quantum chemical methods: dissociation of the N 2 molecule, A comprehensive comparison of different quantum-chemical methods applied to calculate the N 2 ground state potential energy curve is presented. In the comparison we highlight the multireference state-specific (MRSS) coupled-cluster (CC) approach with the complete-activespace (CAS) reference and with single and double excitations from all reference determinants in the CC operator developed in our group. The method is called CASCCSD. The energy and amplitude equations for the method and the corresponding computer code have been generated using a computerized automative procedure that in the present work was extended to produce a parallel computer code. The complete CASCCSD wave function for N 2 includes some selected eight-fold excitations in the CC operator. An analysis of the wave function estimates the importance of those excitations at large internuclear separations.

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CASCCD: Coupled-cluster method with double excitations and the CAS reference

Cited by 75 publications

References 50 publications

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Full configuration interaction calculation of Be3

State-specific multireference complete-active-space coupled-cluster approach versus other quantum chemical methods: dissociation of the N₂molecule

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CASCCD: Coupled-cluster method with double excitations and the CAS reference

Cited by 75 publications

References 50 publications

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Block Correlated Coupled Cluster Theory With A Complete Active-Space Self-Consistent-Field Reference Function: The General Formalism And Applications

Full configuration interaction calculation of Be3

State-specific multireference complete-active-space coupled-cluster approach versus other quantum chemical methods: dissociation of the N2molecule

Contact Info

Product

Resources

About

State-specific multireference complete-active-space coupled-cluster approach versus other quantum chemical methods: dissociation of the N₂molecule