Ab initio no-core solutions for 6 Li

We solve for properties of 6 Li in the ab initio no-core full configuration (NCFC) approach and we separately solve for its ground state and J π = 2 2 + resonance with the Gamow shell model (GSM) in the Berggren basis. We employ both the JISP16 and chiral NNLO opt realistic nucleon–nucleon interactions and investigate the ground state energy, excitation energies, point proton root mean square (rms) radius and a suite of electroweak observables. We also extend and test methods to extrapolate the ground state energy, point proton rms radius, and electric quadrupole moment. We attain improved estimates of these observables in the NCFC approach by using basis spaces up through N max = 18 that enable more definitive comparisons with experiment. Using the density matrix renormalization group approach with the JISP16 interaction, we find that we can significantly improve the convergence of the GSM treatment of the 6 Li ground state and J π = 2 2 + resonance by adopting a natural orbital single-particle basis.