State-specific Brillouin–Wigner multireference coupled cluster study of the F2 molecule: assessment of the a posteriori size-extensivity correction

Pittner, Jiřı́; Šmydke, Jan; Čárský, Petr; Hubač, Ivan

doi:10.1016/s0166-1280(01)00473-0

Cited by 48 publications

(25 citation statements)

References 30 publications

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“…For F 2 , its bond-breaking PES has been studied extensively [14,23,27,90,119,156]. In CAS-BCCC4 calculations, a double-zeta (DZ) basis set [157,158] is employed, and two core orbitals are frozen.…”

Section: Ground-state Bond Breaking Potential Energy Surfacesmentioning

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: Ground-state Bond Breaking Potential Energy Surfacesmentioning

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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“…Earlier work is based on relatively small basis sets. 76 A comprehensive review of theoretically predicted spectroscopic constants of F 2 was given by Pittner et al 77 There also exists an ab initio study 78 of vibrational levels in three electronically excited singlet states of F 2 ͑5 levels in two ⌸ states and ϳ30 levels in a ⌺ state͒. Here, the deviations of the calculated harmonic frequencies from the experimental data range from ϳ100 to ϳ 700 cm −1 .…”

Section: Introductionmentioning

confidence: 99%

Accurate ab initio potential energy curve of F2. III. The vibration rotation spectrum

Bytautas

Matsunaga

Nagata

et al. 2007

The Journal of Chemical Physics

134

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An analytical expression is found for the accurate ab initiopotential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5cm−1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30cm−1 of the experimental value of 12953±8cm−1. The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation,spin-orbit coupling, and scalar relativity. The Dunham analysis [Phys. Rev.41, 721 (1932)] of the spectrum is found to be very accurate. New values are given for the spectroscopic constants. KeywordsAb initio calculations, Dissociation energies, Polynomials, Dissociation, Electron correlation calculations Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 127 (2007) An analytical expression is found for the accurate ab initio potential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F 2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5 cm −1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30 cm −1 of the experimental value of 12 953± 8 cm −1 . The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation, spin-orbit coupling, and scalar relativity. The Dunham analysis ͓Phys. Rev. 41, 721 ͑1932͔͒ of the spectrum is found to be very accurate. New values are given for the spectroscopic constants.

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“…19 The performance of the BWCC method has been assessed by calculations on several small, but "difficult" model systems and diatomic molecules. 15,16,[20][21][22][23][24][25] The efficacy of the implementation 14 and the elimination of the intruder-state problem in BWCC have been demonstrated by calculations of chemically interesting systems of moderate size. [26][27][28][29] Recent reviews of the BWCC theory can be found in Refs.…”

Section: Introductionmentioning

confidence: 99%

Towards the multireference Brillouin–Wigner coupled-clusters method with iterative connected triples: MR BWCCSDT-α approximation

Pittner

Demel

2005

The Journal of Chemical Physics

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We developed and implemented an approximation of the state-specific Brillouin-Wigner coupled-cluster method with singles, doubles, and triples, called MRBWCCSDT-alpha, for a general number of closed- and open-shell reference configurations. The accuracy of the method is assessed on the calculation of the oxygen molecule in the X3sigma(g-), a1delta(g), and b1sigma(g+) states and the results of this multireference treatment are compared with previous MRBWCCSD results and with those obtained by the doubly ionized similarity transformed equation-of-motion CCSD and multireference configuration interaction methods and with experimental spectroscopic data. Explicit tests of the size-extensivity of the MRBWCCSDT-alpha method with iterative size-extensivity correction are also performed.

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State-specific Brillouin–Wigner multireference coupled cluster study of the F2 molecule: assessment of the a posteriori size-extensivity correction

Cited by 48 publications

References 30 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

Accurate ab initio potential energy curve of F2. III. The vibration rotation spectrum

Towards the multireference Brillouin–Wigner coupled-clusters method with iterative connected triples: MR BWCCSDT-α approximation

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