Ab Initio Calculations of Medium-Mass Nuclei with Normal-Ordered Chiral NN+3N Interactions

TL;DR

This paper demonstrates that normal-ordered three-nucleon interactions, when used with chiral Hamiltonians and SRG evolution, enable accurate ab initio calculations of medium-mass nuclei, validating the normal-ordering approximation.

Contribution

It provides a comprehensive benchmark and comparison of normal-ordering approximations and coupled-cluster methods for medium-mass nuclei using chiral NN+3N interactions.

Findings

Normal-ordered two-body approximation is accurate for medium-mass nuclei.

IT-NCSM results agree well with coupled-cluster calculations.

Chiral Hamiltonians show strong predictive power for nuclear structure.

Abstract

We study the use of truncated normal-ordered three-nucleon interactions in ab initio nuclear structure calculations starting from chiral two- plus three-nucleon Hamiltonians evolved consistently with the similarity renormalization group (SRG). We present three key steps: (i) a rigorous benchmark of the normal-ordering approximation in the importance-truncated no-core shell model (IT-NCSM) for 4-He, 16-O, and 40-Ca; (ii) a direct comparison of the IT-NCSM results with coupled-cluster calculations at the singles and doubles level (CCSD) for 16-O; and (iii) first applications of SRG-evolved chiral NN+3N Hamiltonians in CCSD for the medium-mass nuclei 16,24-O and 40,48-Ca. We show that the normal-ordered two-body approximation works very well beyond the lightest isotopes and opens a path for ab initio studies of medium-mass and heavy nuclei with chiral two- plus three-nucleon interactions. At the same time we highlight the predictive power of chiral Hamiltonians.