From closed shells to open shells: Coupled-cluster calculations of atomic nuclei
Pith reviewed 2026-05-16 21:16 UTC · model grok-4.3
The pith
Symmetry-broken and equation-of-motion coupled-cluster methods yield consistent bulk properties for open-shell calcium and nickel nuclei.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Coupled-cluster computations based on symmetry-broken reference states and equation-of-motion techniques offer consistent descriptions of bulk properties across medium-mass isotopic chains, as demonstrated through ground-state energies, two-neutron separation energies, and two-neutron shell gaps in calcium and nickel isotopes.
What carries the argument
Equation-of-motion coupled-cluster expansions and symmetry-broken reference states within coupled-cluster theory for open-shell nuclei.
If this is right
- The methods provide reliable predictions for bulk nuclear observables in open-shell regions.
- Consistency across formulations supports their use for systematic studies of isotopic chains.
- Chiral two- and three-body interactions suffice for accurate descriptions in these mass ranges.
- Extensions to other nuclei and observables become feasible with validated approaches.
Where Pith is reading between the lines
- The agreement suggests that the specific choice of open-shell treatment has limited impact on bulk properties.
- Similar consistency could appear in other medium-mass isotopic chains, enabling wider first-principles mapping.
- The results could guide tests on excitation energies or electromagnetic observables where differences might emerge.
Load-bearing premise
The chiral effective field theory interactions accurately represent nuclear forces for these isotopes and that truncation errors and convergence behave similarly across the compared methods.
What would settle it
A large disagreement between the symmetry-broken and equation-of-motion results for two-neutron separation energies in a specific calcium or nickel isotope would falsify the consistency claim.
Figures
read the original abstract
Coupled-cluster theory is a powerful tool for first-principles calculations of atomic nuclei, enabling accurate predictions of nuclear observables across the Segr\`e chart. While coupled-cluster computations are especially efficient at shell closures, extensions have been developed to tackle open-shell nuclei, by exploiting the equation-of-motion method or by expanding the coupled-cluster wave function on top of a symmetry-breaking (either deformed or superfluid) reference state. In this study, we provide a comprehensive comparison of these different formulations applied to the calcium and nickel isotopes using nuclear two- and three-body interactions from chiral effective field theory. Based on ground-state energies, two-neutron separation energies, and two-neutron shell gaps, different coupled-cluster computations - based on symmetry-broken reference states and equation-of-motion techniques - offer consistent descriptions of bulk properties across medium-mass isotopic chains.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper compares coupled-cluster calculations of calcium and nickel isotopes using chiral EFT two- and three-body interactions. It examines extensions to open-shell systems via symmetry-broken (deformed or superfluid) reference states and via the equation-of-motion method, and reports that the different formulations yield consistent results for ground-state energies, two-neutron separation energies, and two-neutron shell gaps across the isotopic chains.
Significance. If the reported consistency survives quantitative scrutiny with error estimates, the work would provide a useful cross-validation of CC extensions for open-shell nuclei, increasing confidence in ab initio predictions of bulk observables in medium-mass systems where shell closures are absent.
major comments (2)
- [Results section] Results section: the central claim of numerical consistency between symmetry-broken CC and EOM-CC rests on direct comparison of observables, yet no quantitative measures (maximum absolute or relative deviations, rms differences, or comparison against estimated chiral truncation errors) are supplied; without these it is impossible to judge whether agreement exceeds the expected many-body truncation uncertainty.
- [Methods] Methods and convergence discussion: the manuscript must demonstrate that basis-size and truncation errors behave comparably in the symmetry-broken and EOM formulations; if the broken-symmetry reference captures additional correlations that are only partially recovered by the EOM truncation, the observed agreement could be an artifact of the specific model spaces and interactions employed.
minor comments (1)
- [Abstract] Abstract: specify the chiral order and cutoff values of the 2N+3N interactions used, as these are essential for reproducibility and for placing the results in the context of EFT truncation error estimates.
Simulated Author's Rebuttal
We thank the referee for the constructive report and the positive assessment of the significance of our work. We address the two major comments below and will incorporate the suggested improvements in the revised manuscript.
read point-by-point responses
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Referee: [Results section] Results section: the central claim of numerical consistency between symmetry-broken CC and EOM-CC rests on direct comparison of observables, yet no quantitative measures (maximum absolute or relative deviations, rms differences, or comparison against estimated chiral truncation errors) are supplied; without these it is impossible to judge whether agreement exceeds the expected many-body truncation uncertainty.
Authors: We agree that quantitative measures are needed to substantiate the consistency claim. In the revised manuscript we will add a dedicated table (and accompanying text) reporting the maximum absolute and relative deviations, as well as RMS differences, between the symmetry-broken CC and EOM-CC results for ground-state energies, two-neutron separation energies, and shell gaps across the Ca and Ni chains. These deviations will be compared directly to the estimated chiral truncation uncertainties obtained from the EFT power counting. This addition will allow readers to assess whether the observed agreement lies within the expected many-body and interaction uncertainties. revision: yes
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Referee: [Methods] Methods and convergence discussion: the manuscript must demonstrate that basis-size and truncation errors behave comparably in the symmetry-broken and EOM formulations; if the broken-symmetry reference captures additional correlations that are only partially recovered by the EOM truncation, the observed agreement could be an artifact of the specific model spaces and interactions employed.
Authors: We acknowledge the importance of showing that convergence properties are comparable. The revised Methods section will include explicit convergence plots and tables for both formulations, displaying the dependence of the observables on the model-space size (N_max) and on the CC truncation level (CCSD versus CCSDT). We will demonstrate that the residual basis-size and truncation errors are of similar magnitude in the symmetry-broken and EOM calculations for the nuclei considered, thereby supporting that the reported consistency is not an artifact of the chosen spaces or interactions. revision: yes
Circularity Check
No circularity; consistency shown by independent numerical comparisons
full rationale
The paper computes ground-state energies, two-neutron separation energies, and shell gaps for Ca and Ni isotopes using multiple CC variants (symmetry-broken references and EOM-CC) on identical chiral EFT 2N+3N interactions. These are direct, independent many-body calculations whose agreement is an empirical outcome, not a definitional identity or fitted prediction. Prior self-citations describe method development but are not invoked as uniqueness theorems or load-bearing justifications for the observed consistency; the results stand on the numerical output itself. No self-definitional loops, ansatz smuggling, or renaming of known results occur in the derivation chain.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Chiral effective field theory interactions provide a sufficiently accurate description of nuclear forces for medium-mass nuclei
Reference graph
Works this paper leans on
-
[1]
In a second step, the target nucleus with mass numberA=A ∗ ±k (k= 1,2) is interpreted as a generalized excitation of the closed-shell system. The present work focuses onk= 2, and more specifically, we detail the two-particle-removed (2PR) variant [24, 46, 77] in which the target nucleus dif- fers by the removal of two nucleons from the (sub)shell closure....
-
[2]
Hergert, A guided tour of ab initio nuclear many-body theory, Front
H. Hergert, A guided tour of ab initio nuclear many-body theory, Front. Phys.8, 379 (2020)
work page 2020
-
[3]
S. R. Stroberg, J. D. Holt, A. Schwenk, and J. Simonis, Ab initio limits of atomic nuclei, Phys. Rev. Lett.126, 022501 (2021)
work page 2021
-
[4]
Papenbrock, Ab initio computations of atomic nuclei (2024), arXiv:2410.00843 [nucl-th]
T. Papenbrock, Ab initio computations of atomic nuclei (2024), arXiv:2410.00843 [nucl-th]
-
[5]
B. Hu, W. Jiang, T. Miyagi, Z. Sun, A. Ekström, C. Forssén, G. Hagen, J. D. Holt, T. Papenbrock, S. R. Stroberg, and I. Vernon, Ab initio predictions link the neutron skin of 208Pbto nuclear forces, Nature Physics 18, 1196 (2022)
work page 2022
-
[6]
P. Arthuis, K. Hebeler, and A. Schwenk, Neutron-rich nuclei and neutron skins from chiral low-resolution inter- actions (2024), arXiv:2401.06675 [nucl-th]
-
[7]
K. Hebeler, V. Durant, J. Hoppe, M. Heinz, A. Schwenk, J. Simonis, and A. Tichai, Normal ordering of three- nucleon interactions for ab initio calculations of heavy nuclei, Phys. Rev. C107, 024310 (2023)
work page 2023
-
[8]
F. Bonaiti, G. Hagen, and T. Papenbrock, Structure of the doubly magic nuclei208Pb and 266Pb from ab initio computations (2025), arXiv:2508.14217 [nucl-th]
-
[9]
R. Machleidt and F. Sammarruca, Recent advances in chiral eft based nuclear forces and their applications, Prog. Part. Nucl. Phys.137, 104117 (2024)
work page 2024
-
[10]
Epelbaum, Chiral symmetry and nuclear interactions, Few-Body Systems65(2024)
E. Epelbaum, Chiral symmetry and nuclear interactions, Few-Body Systems65(2024)
work page 2024
- [11]
- [12]
-
[13]
H. Hergert, S. Bogner, T. Morris, A. Schwenk, and K. Tsukiyama, The in-medium similarity renormalization group: A novel ab initio method for nuclei, Phys. Rep. 621, 165 (2016)
work page 2016
- [14]
-
[15]
W. Dickhoff and C. Barbieri, Self-consistent green’s func- tion method for nuclei and nuclear matter, Prog. Part. Nucl. Phys.52, 377 (2004)
work page 2004
-
[16]
Somà, Self-consistent green’s function theory for atomic nuclei, Front
V. Somà, Self-consistent green’s function theory for atomic nuclei, Front. Phys.8, 340 (2020)
work page 2020
-
[17]
V. Somà, P. Navrátil, F. Raimondi, C. Barbieri, and T. Duguet, Novel chiral hamiltonian and observables in light and medium-mass nuclei, Phys. Rev. C101, 014318 (2020)
work page 2020
-
[18]
I. Shavitt and R. J. Bartlett,Many-Body Methods in Chemistry and Physics: MBPT and Coupled-Cluster Theory, Cambridge Molecular Science (Cambridge Uni- versity Press, 2009)
work page 2009
-
[19]
R. J. Bartlett and M. Musiał, Coupled-cluster theory in quantum chemistry, Rev. Mod. Phys.79, 291 (2007)
work page 2007
- [20]
- [21]
- [22]
-
[23]
J. R. Gour, P. Piecuch, M. Hjorth-Jensen, M. Włoch, and D. J. Dean, Coupled-cluster calculations for valence systems around 16O, Phys. Rev. C74, 024310 (2006)
work page 2006
-
[24]
A. I. Krylov, Equation-of-motion coupled-cluster meth- ods for open-shell and electronically excited species: The hitchhiker’s guide to fock space, Annual Review of Phys- ical Chemistry59, 433 (2008)
work page 2008
-
[25]
G. R. Jansen, M. Hjorth-Jensen, G. Hagen, and T. Pa- penbrock, Toward open-shell nuclei with coupled-cluster theory, Phys. Rev. C83, 054306 (2011)
work page 2011
-
[26]
G. R. Jansen, Spherical coupled-cluster theory for open- shell nuclei, Phys. Rev. C88, 024305 (2013)
work page 2013
-
[27]
V. Somà, T. Duguet, and C. Barbieri, Ab initio self-consistent gorkov-green’s function calculations of semimagic nuclei: Formalism at second order with a two- nucleon interaction, Phys. Rev. C84, 064317 (2011)
work page 2011
-
[28]
A. Signoracci, T. Duguet, G. Hagen, and G. R. Jansen, Abinitiobogoliubovcoupledclustertheoryforopen-shell nuclei, Phys. Rev. C91, 064320 (2015)
work page 2015
- [29]
- [30]
-
[31]
Z. H. Sun, A. Ekström, C. Forssén, G. Hagen, G. R. Jansen, and T. Papenbrock, Multiscale physics of atomic nuclei from first principles, Phys. Rev. X15, 011028 (2025)
work page 2025
-
[32]
S. K. Bogner, H. Hergert, J. D. Holt, A. Schwenk, S. Binder, A. Calci, J. Langhammer, and R. Roth, Nonperturbative shell-model interactions from the in- medium similarity renormalization group, Phys. Rev. Lett.113, 142501 (2014). 13
work page 2014
-
[33]
G.R.Jansen, J.Engel, G.Hagen, P.Navratil,andA.Sig- noracci,Ab Initiocoupled-cluster effective interactions for the shell model: Application to neutron-rich oxy- gen and carbon isotopes, Phys. Rev. Lett.113, 142502 (2014)
work page 2014
-
[34]
S. R. Stroberg, H. Hergert, S. K. Bogner, and J. D. Holt, Nonempiricalinteractionsforthenuclearshellmodel: An update, Annual Review of Nuclear and Particle Science 69, 307 (2019)
work page 2019
- [35]
-
[36]
H. Hergert, S. K. Bogner, T. D. Morris, S. Binder, A. Calci, J. Langhammer, and R. Roth, Ab initio mul- tireference in-medium similarity renormalization group calculations of even calcium and nickel isotopes, Phys. Rev. C90, 041302 (2014)
work page 2014
- [37]
-
[38]
M. Frosini, T. Duguet, J.-P. Ebran, and V. Somà, Multi- reference many-body perturbation theory for nuclei: I. Novel PGCM-PT formalism, Eur. Phys. J. A58, 62 (2022)
work page 2022
-
[39]
M. Frosini, T. Duguet, J.-P. Ebran, B. Bally, H. Hergert, T. R. Rodríguez, R. Roth, J. Yao, and V. Somà, Multi- reference many-body perturbation theory for nuclei: III. Ab initio calculations at second order in PGCM-PT, Eur. Phys. J. A58, 64 (2022)
work page 2022
-
[40]
D. I. Lyakh, M. Musiał, V. F. Lotrich, and R. J. Bartlett, Multireference nature of chemistry: The coupled-cluster view, Chemical Reviews112, 182 (2012)
work page 2012
-
[41]
A. Köhn, M. Hanauer, L. A. Mück, T.-C. Jagau, and J. Gauss, State-specific multireference coupled-cluster theory, WIREs Computational Molecular Science3, 176 (2013)
work page 2013
- [42]
-
[43]
N. M. Parzuchowski, T. D. Morris, and S. K. Bogner, Ab initio excited states from the in-medium similarity renormalization group, Phys. Rev. C95, 044304 (2017)
work page 2017
-
[44]
N.M.Parzuchowski, S.R.Stroberg, P.Navrátil, H.Herg- ert, and S. K. Bogner, Ab initio electromagnetic ob- servables with the in-medium similarity renormalization group, Phys. Rev. C96, 034324 (2017)
work page 2017
- [45]
-
[46]
A. Ekström, G. R. Jansen, K. A. Wendt, G. Hagen, T. Papenbrock, S. Bacca, B. Carlsson, and D. Gazit, Ef- fects of three-nucleon forces and two-body currents on gamow-teller strengths, Phys. Rev. Lett.113, 262504 (2014)
work page 2014
- [47]
- [48]
- [49]
-
[50]
M. Miorelli, S. Bacca, N. Barnea, G. Hagen, G. R. Jansen, G. Orlandini, and T. Papenbrock, Electric dipole polarizability from first principles calculations, Phys. Rev. C94, 034317 (2016)
work page 2016
-
[51]
J. E. Sobczyk, B. Acharya, S. Bacca, and G. Hagen, Ab initio computation of the longitudinal response function in 40Ca, Phys. Rev. Lett.127, 072501 (2021)
work page 2021
-
[52]
F. Bonaiti, A. Porro, S. Bacca, A. Schwenk, and A. Tichai, Ab initio calculations of monopole sum rules: From finite nuclei to infinite nuclear matter (2025), arXiv:2511.15836 [nucl-th]
-
[53]
F. Bonaiti, S. Bacca, G. Hagen, and G. R. Jansen, Electromagnetic observables of open-shell nuclei from coupled-cluster theory, Phys. Rev. C110, 044306 (2024)
work page 2024
- [54]
-
[55]
V. Somà, A. Cipollone, C. Barbieri, P. Navrátil, and T. Duguet, Chiral two- and three-nucleon forces along medium-mass isotope chains, Phys. Rev. C89, 061301 (2014)
work page 2014
-
[56]
Papugaet al.(IS484), Shell structure of potassium isotopes deduced from their magnetic moments, Phys
J. Papugaet al.(IS484), Shell structure of potassium isotopes deduced from their magnetic moments, Phys. Rev. C90, 034321 (2014)
work page 2014
- [57]
-
[58]
S. J. Novario, G. Hagen, G. R. Jansen, and T. Papen- brock, Charge radii of exotic neon and magnesium iso- topes, Phys. Rev. C102, 051303 (2020)
work page 2020
-
[59]
B. Hu, Z. H. Sun, G. Hagen, and T. Papenbrock, Ab ini- tio computations of strongly deformed nuclei near80Zr, Phys. Rev. C110, L011302 (2024)
work page 2024
-
[60]
B. Hu, Z. Sun, G. Hagen, G. Jansen, and T. Papenbrock, Ab initio computations from 78Ni towards 70Ca along neutron number N=50, Physics Letters B858, 139010 (2024)
work page 2024
-
[61]
J. A. Sheikh and P. Ring, Symmetry projected Hartree- Fock-Bogolyubov equations, Nucl. Phys. A665, 71 (2000), arXiv:nucl-th/9907065
work page internal anchor Pith review Pith/arXiv arXiv 2000
-
[62]
Duguet, Symmetry broken and restored coupled- cluster theory: I
T. Duguet, Symmetry broken and restored coupled- cluster theory: I. rotational symmetry and angular mo- mentum, J. Phys. G42, 025107 (2014)
work page 2014
-
[63]
Y. Qiu, T. M. Henderson, J. Zhao, and G. E. Scuseria, Projected coupled cluster theory, J. Chem. Phys147, 064111 (2017)
work page 2017
-
[64]
T. Duguet and A. Signoracci, Symmetry broken and re- storedcoupled-clustertheory: II.Globalgaugesymmetry and particle number, J. Phys. G44, 015103 (2016)
work page 2016
-
[65]
Y. Qiu, T. M. Henderson, T. Duguet, and G. E. Scuseria, Particle-number projected Bogoliubov-coupled- cluster theory: Application to the pairing Hamiltonian, Phys. Rev. C99, 044301 (2019)
work page 2019
-
[66]
Papenbrock, Effective field theory of pairing rotations, Phys
T. Papenbrock, Effective field theory of pairing rotations, Phys. Rev. C105, 044322 (2022)
work page 2022
- [67]
-
[68]
M. Frosini, T. Duguet, B. Bally, Y. Beaujeault-Taudière, J. P. Ebran, and V. Somà, In-mediumk-body reduction ofn-body operators: A flexible symmetry-conserving ap- proach based on the sole one-body density matrix, Eur. Phys. J. A57, 151 (2021)
work page 2021
-
[69]
Y. S. Lee, S. A. Kucharski, and R. J. Bartlett, A coupled cluster approach with triple excitations, J. Chem. Phys. 81, 5906 (1984)
work page 1984
-
[70]
R. J. Bartlett, Perspective on coupled-cluster theory. the evolution toward simplicity in quantum chemistry, Phys. Chem. Chem. Phys.26, 8013 (2024)
work page 2024
- [71]
-
[72]
Z. H. Sun, C. A. Bell, G. Hagen, and T. Papenbrock, How to renormalize coupled cluster theory, Phys. Rev. C 106, L061302 (2022)
work page 2022
-
[73]
P. Demol,Ab initio description of singly open-shell nu- clei via Bogoliubov coupled-cluster theory, Ph.D. thesis (2024), prepared under the supervision of T. Duguet, R. Raabe and A. Tichai, KU Leuven, Belgium, 2024
work page 2024
-
[74]
A. Scalesi, T. Duguet, P. Demol, M. Frosini, V. Somà, and A. Tichai, Impact of correlations on nuclear bind- ing energies: Ab initio calculations of singly and doubly open-shell nuclei, Eur. Phys. J. A60, 209 (2024)
work page 2024
-
[75]
A. Bohr and B. R. Mottelson,Nuclear structure. Volume II. Nuclear deformations(Addison-Wesley/W. A. Ben- jamin, Inc., Reading, MA, 1974)
work page 1974
- [76]
-
[77]
G. Hagen and H. A. Nam, Computational aspects of nuclear coupled-cluster theory, Progress of Theoretical Physics Supplement196, 102 (2012)
work page 2012
-
[78]
J. Shen and P. Piecuch, Doubly electron-attached and doubly ionized equation-of-motion coupled-cluster meth- ods with 4-particle–2-hole and 4-hole–2-particle exci- tations and their active-space extensions, Jour. Chem. Phys.138, 194102 (2013)
work page 2013
-
[79]
M.Musiał, S.A.Kucharski,andR.J.Bartlett,Equation- of-motion coupled cluster method with full inclusion of the connected triple excitations for ionized states: IP- EOM-CCSDT, J. Chem. Phys118, 1128 (2003)
work page 2003
-
[80]
S. Gulania, E. F. Kjønstad, J. F. Stanton, H. Koch, and A. I. Krylov, Equation-of-motion coupled-cluster method with double electron-attaching operators: Theory, imple- mentation, and benchmarks, J. Chem. Phys154(2021)
work page 2021
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