Quasiparticle Fock-space coupled-cluster theory

Stolarczyk, Leszek Z.; Monkhorst, Hendrik J.

doi:10.1080/00268976.2010.518981

Cited by 19 publications

(33 citation statements)

References 50 publications

(152 reference statements)

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“…The cluster operator we have introduced is the simplest useful form for T and is a generalization of p-CCD to the BCS case, though we remind the reader that, for the pairing Hamiltonian, p-CCD and the full CCD model are identical. We note that CC theory has been formulated in a quasiparticle basis before [22], but with a restriction that the wave function does not break number symmetry.…”

Section: Quasiparticle Coupled Cluster Theorymentioning

confidence: 99%

Quasiparticle coupled cluster theory for pairing interactions

et al. 2014

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We present an extension of the pair coupled cluster doubles (p-CCD) method to quasiparticles and apply it to the attractive pairing Hamiltonian. Near the transition point where number symmetry gets spontaneously broken, the proposed BCS-based p-CCD method yields energies significantly better than those of existing methods when compared to the exact results obtained via solution of the Richardson equations. The quasiparticle p-CCD method has a low computational cost of O(N 3 ) as a function of system size. This together with the high quality of results here demonstrated points to considerable promise for the accurate description of strongly correlated systems with more realistic pairing interactions.

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Section: Quasiparticle Coupled Cluster Theorymentioning

confidence: 99%

Quasiparticle coupled cluster theory for pairing interactions

et al. 2014

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“…We formulate a workable Bogoliubov coupled cluster (BCC) theory for nuclei by representing the exact ground-state wavefunction of even-even open-shell nuclei as the exponential of a quasiparticle excitation cluster operator acting on a Bogoliubov reference state in order to extend the reach of single-reference coupled cluster calculations [27]. A reduced form of this theory based on a Bardeen-CooperSchrieffer (BCS) reference state was already formulated and applied to simplified, e.g.…”

Section: Introductionmentioning

confidence: 99%

Ab initioBogoliubov coupled cluster theory for open-shell nuclei

et al. 2015

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Background: Ab initio many-body methods have been developed over the past ten years to address closed-shell nuclei up to mass A ∼ 130 on the basis of realistic two-and three-nucleon interactions. A current frontier relates to the extension of those many-body methods to the description of open-shell nuclei.Purpose: Several routes to address open-shell nuclei are currently under investigation, including ideas which exploit spontaneous symmetry breaking. Singly open-shell nuclei can be efficiently described via the sole breaking of U (1) gauge symmetry associated with particle-number conservation, as a way to account for their superfluid character. While this route was recently followed within the framework of self-consistent Green's function theory, the goal of the present work is to formulate a similar extension within the framework of coupled cluster theory.Methods: We formulate and apply Bogoliubov coupled cluster (BCC) theory, which consists of representing the exact ground-state wavefunction of the system as the exponential of a quasiparticle excitation cluster operator acting on a Bogoliubov reference state. Equations for the ground-state energy and the cluster amplitudes are derived at the singles and doubles level (BCCSD) both algebraically and diagrammatically. The formalism includes three-nucleon forces at the normal-ordered two-body level. The first BCCSD code is implemented in m-scheme, which will permit the treatment of doubly open-shell nuclei via the further breaking of SU (2) symmetry associated with angular momentum conservation.Results: Proof-of-principle calculations in an Nmax = 6 spherical harmonic oscillator basis are performed for 16,18,20 O, 18 Ne, and 20 Mg in the BCCD approximation with a chiral two-nucleon interaction, comparing to results obtained in standard coupled cluster theory when applicable. The breaking of U (1) symmetry is monitored by computing the variance associated with the particle-number operator. Conclusions:The newly developed many-body formalism increases the potential span of ab initio calculations based on single-reference coupled cluster techniques tremendously, i.e. potentially to reach several hundred additional mid-mass nuclei. The new formalism offers a wealth of potential applications and further extensions dedicated to the description of ground-and excited-states of open-shell nuclei. Short-term goals include the implementation of three-nucleon forces at the normal-ordered two-body level. Mid-term extensions include the approximate treatment of triple corrections and the development of the equation-of-motion methodology to treat both excited states and odd nuclei. Long-term extensions include exact restoration of U (1) and SU (2) symmetries.

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“…Historically, another approach to multireference CC theory has emerged from the ansatz, Eq. (11), namely, valence‐universal or Fock‐space CC theory 31–36. Here, analogous to the state‐universal variant of the JM ansatz, a wave‐operator \documentclass{article}\usepackage{amssymb}\begin{document}\pagestyle{empty}$\hat{\Omega } $\end{document} generates correlated states by acting on states from the model space.…”

Section: Ansätze For Mrcc Wavefunctionsmentioning

confidence: 99%

State‐specific multireference coupled‐cluster theory

Köhn

Hanauer

Mück

et al. 2012

WIREs Comput Mol Sci

127

106

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The multireference problem is considered one of the great challenges in coupled‐cluster (CC) theory. Most recent developments are based on state‐specific approaches, which focus on a single state and avoid some of the numerical problems of more general approaches. We review various state‐of‐the‐art methods, including Mukherjee's state‐specific multireference coupled‐cluster (Mk‐MRCC) theory, multireference Brillouin–Wigner coupled‐cluster (MR‐BWCC) theory, the MRexpT method, and internally contracted multireference coupled‐cluster (ic‐MRCC) theory. Related methods such as extended single‐reference schemes [e.g., the complete active space coupled‐cluster (CASCC) theory] and canonical transformation (CT) theory are covered as well. The comparison is done on the basis of formal arguments, implementation issues, and numerical results. Although a final and generally accepted multireference CC theory is still lacking, it is emphasized that recent developments render the new MRCC schemes useful tools for solving chemical problems. © 2012 John Wiley & Sons, Ltd. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods

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Quasiparticle Fock-space coupled-cluster theory

Cited by 19 publications

References 50 publications

Quasiparticle coupled cluster theory for pairing interactions

Quasiparticle coupled cluster theory for pairing interactions

Ab initioBogoliubov coupled cluster theory for open-shell nuclei

State‐specific multireference coupled‐cluster theory

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