Largescale exact diagonalizations reveal lowmomentum scales of nuclei
Ab initio methods aim to solve the nuclear manybody problem with controlled approximations. Virtually exact numerical solutions for realistic interactions can only be obtained for certain special cases such as fewnucleon systems. In this paper, we extend the reach of exact diagonalization methods to handle model spaces with dimension exceeding $${10}^{10}$$ on a single compute node. This allows us to perform nocore shell model (NCSM) calculations for $$^{6}\mathrm{Li}$$ in model spaces up to $${N}_{\mathrm{max}}=22$$ and to reveal the $$^{4}\mathrm{He}$$+d halo structure of this nucleus. Still, the use of a finite harmonicoscillator basis implies truncations in both infrared (IR) and ultraviolet (UV) length scales. These truncations impose finitesize corrections on observables computed in this basis. We perform IR extrapolations of energies and radii computed in the NCSM and with the coupledcluster method at several fixed UV cutoffs. It is shown that this strategy enables information gain also from data that is not fully UV converged. IR extrapolations improve the accuracy of relevant boundstate observables for a range of UV cutoffs, thus making them profitable tools. We relate the momentum scale that governs the exponential IR convergence to the threshold energy for the first open decay channel. Finally, using largescale NCSM calculations we numerically verify this smallmomentum scale of finite nuclei.
 Authors:

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 Chalmers Univ. of Technology, Göteborg (Sweden). Dept. of Physics
 Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Physics Division
 Publication Date:
 Grant/Contract Number:
 AC0500OR22725; FG0296ER40963; SC0008499; SC0018223; IG20125158
 Type:
 Accepted Manuscript
 Journal Name:
 Physical Review C
 Additional Journal Information:
 Journal Volume: 97; Journal Issue: 3; Journal ID: ISSN 24699985
 Publisher:
 American Physical Society (APS)
 Research Org:
 Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States); Chalmers Univ. of Technology, Göteborg (Sweden)
 Sponsoring Org:
 USDOE Office of Science (SC), Nuclear Physics (NP) (SC26); Swedish Foundation for International Cooperation in Research and Higher Education (STINT)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; fewbody systems; nuclear manybody theory; nuclear structure & decays; ab initio calculations
 OSTI Identifier:
 1471876
 Alternate Identifier(s):
 OSTI ID: 1430150
Forssén, C., Carlsson, B. D., Johansson, H. T., Sääf, D., Bansal, A., Hagen, G., and Papenbrock, T.. Largescale exact diagonalizations reveal lowmomentum scales of nuclei. United States: N. p.,
Web. doi:10.1103/PhysRevC.97.034328.
Forssén, C., Carlsson, B. D., Johansson, H. T., Sääf, D., Bansal, A., Hagen, G., & Papenbrock, T.. Largescale exact diagonalizations reveal lowmomentum scales of nuclei. United States. doi:10.1103/PhysRevC.97.034328.
Forssén, C., Carlsson, B. D., Johansson, H. T., Sääf, D., Bansal, A., Hagen, G., and Papenbrock, T.. 2018.
"Largescale exact diagonalizations reveal lowmomentum scales of nuclei". United States.
doi:10.1103/PhysRevC.97.034328. https://www.osti.gov/servlets/purl/1471876.
@article{osti_1471876,
title = {Largescale exact diagonalizations reveal lowmomentum scales of nuclei},
author = {Forssén, C. and Carlsson, B. D. and Johansson, H. T. and Sääf, D. and Bansal, A. and Hagen, G. and Papenbrock, T.},
abstractNote = {Ab initio methods aim to solve the nuclear manybody problem with controlled approximations. Virtually exact numerical solutions for realistic interactions can only be obtained for certain special cases such as fewnucleon systems. In this paper, we extend the reach of exact diagonalization methods to handle model spaces with dimension exceeding ${10}^{10}$ on a single compute node. This allows us to perform nocore shell model (NCSM) calculations for $^{6}\mathrm{Li}$ in model spaces up to ${N}_{\mathrm{max}}=22$ and to reveal the $^{4}\mathrm{He}$+d halo structure of this nucleus. Still, the use of a finite harmonicoscillator basis implies truncations in both infrared (IR) and ultraviolet (UV) length scales. These truncations impose finitesize corrections on observables computed in this basis. We perform IR extrapolations of energies and radii computed in the NCSM and with the coupledcluster method at several fixed UV cutoffs. It is shown that this strategy enables information gain also from data that is not fully UV converged. IR extrapolations improve the accuracy of relevant boundstate observables for a range of UV cutoffs, thus making them profitable tools. We relate the momentum scale that governs the exponential IR convergence to the threshold energy for the first open decay channel. Finally, using largescale NCSM calculations we numerically verify this smallmomentum scale of finite nuclei.},
doi = {10.1103/PhysRevC.97.034328},
journal = {Physical Review C},
number = 3,
volume = 97,
place = {United States},
year = {2018},
month = {3}
}