Deformed in-medium similarity renormalization group

TL;DR

This paper introduces an ab initio deformed IMSRG method for open-shell nuclei, combining deformed Hartree-Fock basis with correlation energy estimates, improving the description of deformed nuclei and benchmarking against other models.

Contribution

The work develops a deformed IMSRG approach that incorporates static correlations via angular momentum projection and applies it to various isotopes, enhancing nuclear structure calculations.

Findings

Accurately calculated energies and radii for beryllium and magnesium isotopes.

Benchmark results show good agreement with no-core shell model and valence-space IMSRG.

Extrapolation methods improve the comparison with experimental data.

Abstract

We have developed an {\it ab initio} deformed in-medium similarity renormalization group (IMSRG) for open-shell nuclei. This is a single-reference IMSRG in deformed Hartree-Fock (HF) basis. Deformed wave functions are more efficient in describing deformed nuclei. The broken spherical symmetry needs to be restored by angular momentum projection, which is computational expensive. The angular momentum mainly capture the static correlations and can be estimated by the projection of the HF state. In this work, we do deformed IMSRG calculation and add the correlation energy from projected HF as a leading order approximation. As the test ground, we have calculated the deformed $^{8,10}\rm Be$ isotopes with the optimized chiral interaction NNLO$_{\rm opt}$. The results are benchmarked with the no-core shell model and valence space IMSRG calculations. Then we systematically investigated the ground-state energies and charge radii of even-even isotopes from light beryllium to medium-mass magnesium. The calculated energies are extrapolated to infinite basis space by an exponential form, and compared with the extrapolated valence-space IMSRG results and experimental data available.