Abstract
We report ab initio calculations for neutron drops in a 10 MeV external harmonic-oscillator trap using chiral nucleon–nucleon plus three-nucleon interactions. We present total binding energies, internal energies, radii and odd–even energy differences for neutron numbers N=2–18 using the no-core shell model with and without importance truncation. Furthermore, we present total binding energies for N=8,16,20,28,40,50 obtained in a coupled-cluster approach. Comparisons with quantum Monte Carlo results, where available, using Argonne v8′ with three-nucleon interactions reveal important dependences on the chosen Hamiltonian.
Highlights
There has been significant interest in ab initio solutions for systems of neutron drops trapped in external potentials aimed at providing insights into properties of unstable neutron-rich nuclei and neutron star matter [1, 2, 3, 4]
Since we find the convergence pattern for all other neutron numbers very similar to that shown in Fig. 1, we will quote the lowest energy for fixed neutron number at the largest Nmax obtained as our final result for the total ground state energy
We show our results with the Argonne v8 (AV8) plus 3N interactions (UIX and IL7) auxiliary field diffusion Monte Carlo (AFDMC) results from Refs. [3, 4] in Fig. 2. (Ref. [4] provides multiple states with different J for odd neutron drops; in all of our figures with AV8, AV8 +Urbana IX (UIX) or AV8 +IL7 we use the states with lowest total energy for comparison with our results.) To highlight the difference in the sensitivity to the 3N interaction, we provide an inset in Fig. 2 depicting the ratio of the results with the initial NN+3N interaction to those with the initial NN interaction alone
Summary
There has been significant interest in ab initio solutions for systems of neutron drops trapped in external potentials aimed at providing insights into properties of unstable neutron-rich nuclei and neutron star matter [1, 2, 3, 4]. Comparisons of neutron drop results using different microscopic interactions provide information on the isovector part of the nucleon-nucleon (NN) interaction and the T = 3/2 component of the three-nucleon (3N) interaction. With these goals in mind, we present the first ab initio results for pure neutron systems using chiral NN+3N Hamiltonians in an external trap and compare with results previously obtained using high-precision phenomenological NN+3N Hamiltonians. [2, 4] for the configuration interaction approach to trapped neutron drops in the current application. We make use of the similarity renormalization group (SRG) approach [24, 25, 26, 27, 28, 29] that provides a straightforward and flexible framework for consistently evolving (softening) the Hamiltonian and other operators, including 3N interactions [12, 30, 31]
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