Natural orbitals for many-body expansion methods

Abstract

The nuclear many-body problem for medium-mass systems is commonly addressed using wave-function expansion methods that build upon a second-quantized representation of many-body operators with respect to a chosen computational basis. While various options for the computational basis are available, perturbatively constructed natural orbitals recently have been shown to lead to significant improvement in many-body applications yielding faster model-space convergence and lower sensitivity to basis set parameters in large-scale no-core shell model diagonalizations. This work provides a detailed comparison of single-particle basis sets and a systematic benchmark of natural orbitals in nonperturbative many-body calculations using the in-medium similarity renormalization group approach. As a key outcome we find that the construction of natural orbitals in a large single-particle basis enables for performing the many-body calculation in a reduced space of much lower dimension, thus offering significant computational savings in practice that help extend the reach of ab initio methods towards heavier masses and higher accuracy.

arXiv comment15 pages, 9 figures, published version

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• Angular-momentum projection in coupled-cluster theory: structure of ${}^{34}$Mg
• In-medium similarity renormalization group with three-body operators
• Beyond-mean-field approaches for nuclear neutrinoless double beta decay in the standard mechanism
• Measures of complexity and entanglement in fermionic many-body systems
• In-medium $k$-body reduction of $n$-body operators
• Normal ordering of three-nucleon interactions for ab initio calculations of heavy nuclei
• Towards heavy-mass ab initio nuclear structure: Open-shell Ca, Ni and Sn isotopes from Bogoliubov coupled-cluster theory
• Ab initio structure factors for spin-dependent dark matter direct detection
• Improved structure of calcium isotopes from ab initio calculations
• Nuclear charge radii of Na isotopes: A tale of two theories
• Natural orbitals for the ab initio no-core configuration interaction approach
• Beta Decay in Medium-Mass Nuclei with the In-Medium Similarity Renormalization Group
• The nuclear charge radius of ${}^{13}\mathrm{C}$
• Coupled-cluster theory for strong entanglement in nuclei
• Least-square approach for singular value decompositions of scattering problems
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• Ab initio computations of the fourth-order charge density moments of ${}^{48}$Ca and ${}^{208}$Pb
• Non-Markovian character and irreversibility of real-time quantum many-body dynamics
• Importance truncation for the in-medium similarity renormalization group
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• Modewise Johnson-Lindenstrauss Embeddings for Nuclear Many-Body Theory
• Deformed natural orbitals for ab initio calculations
• Normal-ordering approximations and translational (non) invariance
• Universal trend of charge radii of even-even Ca-Zn nuclei