Convergence of many-body truncations in the in-medium similarity renormalization group
Abstract
The in-medium similarity renormalization group (IMSRG) is a leading \textit{ab initio} method for describing atomic nuclei. Most applications truncate the flowing operators at the normal-ordered two-body level, neglecting induced higher-body terms. Convergence with increasing operator rank remains poorly understood, particularly in strongly correlated systems. We systematically assess the many-body truncation hierarchy in the single-reference and multi-reference IMSRG, retaining normal-ordered operators through the four-body and three-body levels, respectively. Using an exactly solvable pairing-plus-particle-hole model, we quantify successive higher-body corrections over a broad range of interaction strengths, spanning weakly to strongly correlated regimes. The multi-reference formulation exhibits faster and more robust convergence than its single-reference counterpart, with the advantage becoming most pronounced at strong coupling. In this regime, higher-rank irreducible density matrices play an essential role in achieving convergence of the many-body expansion.
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BibTeX
@misc{chen2026convergence,
title = {{Convergence of many-body truncations in the in-medium similarity renormalization group}},
author = {L. H. Chen and H. Hergert and J. M. Yao},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.01458},
eprint = {2611.01458},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.01458},
}
RIS
TY - UNPB
TI - Convergence of many-body truncations in the in-medium similarity renormalization group
AU - L. H. Chen
AU - H. Hergert
AU - J. M. Yao
PY - 2026
DA - 2026/11/01
PB - arXiv
DO - 10.48550/arxiv.2611.01458
UR - https://arxiv.org/abs/2611.01458
AB - The in-medium similarity renormalization group (IMSRG) is a leading \textit{ab initio} method for describing atomic nuclei. Most applications truncate the flowing operators at the normal-ordered two-body level, neglecting induced higher-body terms. Convergence with increasing operator rank remains poorly understood, particularly in strongly correlated systems. We systematically assess the many-body truncation hierarchy in the single-reference and multi-reference IMSRG, retaining normal-ordered operators through the four-body and three-body levels, respectively. Using an exactly solvable pairing-plus-particle-hole model, we quantify successive higher-body corrections over a broad range of interaction strengths, spanning weakly to strongly correlated regimes. The multi-reference formulation exhibits faster and more robust convergence than its single-reference counterpart, with the advantage becoming most pronounced at strong coupling. In this regime, higher-rank irreducible density matrices play an essential role in achieving convergence of the many-body expansion.
ER -