Ab InitioCalculations of Even Oxygen Isotopes with Chiral Two-Plus-Three-Nucleon Interactions

Abstract

We formulate the in-medium similarity renormalization group (IM-SRG) for open-shell nuclei using a multireference formalism based on a generalized Wick theorem introduced in quantum chemistry. The resulting multireference IM-SRG (MR-IM-SRG) is used to perform the first ab initio study of all even oxygen isotopes with chiral nucleon-nucleon and three-nucleon interactions, from the proton to the neutron drip lines. We obtain an excellent reproduction of experimental ground-state energies with quantified uncertainties, which is validated by results from the importance-truncated no-core shell model and the coupled cluster method. The agreement between conceptually different many-body approaches and experiment highlights the predictive power of current chiral two- and three-nucleon interactions, and establishes the MR-IM-SRG as a promising new tool for ab initio calculations of medium-mass nuclei far from shell closures.

Chiral three-nucleon forces and the evolution of correlations along the oxygen isotopic chain

“…This is well within the estimated theoretical errors discussed above [19]. The dot-dashed line shows the trend of ground state energies for the full Hamiltonian obtained form Gorkov, which include the 18 …”

“…These allow to fully exploit modern chiral interactions with two-nucleon (NN) and 3NFs evolved through SRG techniques [28]. Moreover, open shell nuclei have become arXiv:1412.0491v2 [nucl-th] 19 Jun 2015 accessible through a Gorkov extension of the SCGF formalism [22,29,30], multi-reference IM-SRG [18,23] and Bogoliubov coupled cluster (BCC) [31]. These ab initio studies have mainly focussed on ground state properties, such as total binding energies and two-nucleon separation energies.…”

In-medium similarity renormalization group for closed and open-shell nuclei

“…MR-IMSRG(2) calculations were performed using the Brillouin generator (e max = 14, E 3max = 14, and optimal ω), updating earlier results shown in Refs. [55,62]. Note that the ADC(3) Self-Consistent Green's Function results [128,159] were obtained for λ = 2.0 fm −1 , but the dependence of energies on λ is very weak.…”

“…Truncations in the SRG flow equation cause a violation of unitarity that manifests as a (residual) dependence of many-body results on λ. By varying this parameter, the size of the missing contributions can be assessed (see, e.g., [33,55,57,61,91,[99][100][101][102]). State-of-the-art SRG evolutions of nuclear interactions are nowadays performed in the three-body system, using relative (Jacobi) harmonic oscillator [54,100,103], relative momentum plane wave [101], or momentum-space hypherspherical harmonics representations [104].…”

“…The decoupling of low-and high-momentum modes of the interaction leads to a greatly improved convergence behavior, which in turn extends the range of nuclei a many-body method can be applied to. With SRG-evolved interactions, the No-Core Shell Model (NCSM) and related large-scale diagonalization methods can be extended into the lower sd−shell [53][54][55][56], and methods with systematic many-body truncations like Coupled Cluster (CC) are nowadays applied to nuclei as heavy as tin [57][58][59].…”