W. Erich Ormand

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One approach for solving interactingmany-fermion systems is the configuration-interactionmethod, also sometimes called the interacting shell model, where one finds eigenvalues of the Hamiltonian in a manybody basis of Slater determinants (antisymmetrized products of single-particle wavefunctions). The resulting Hamiltonian matrix is typically very sparse,(More)
The <i>configuration-interaction</i> (CI) method, long a popular approach to describe quantum many-body systems, is cast as a very large sparse matrix eigenpair problem with matrices whose dimension can exceed one billion. Such formulations place high demands on memory capacity and memory bandwidth --- two quantities at a premium today. In this paper, we(More)
Recent developments in nuclear theory allow us to make a connection between quantum chromodynamics (QCD) and low-energy nuclear physics. First, chiral effective field theory (χEFT) provides a natural hierarchy to define two-nucleon (NN), three-nucleon (NNN), and even four-nucleon interactions. Second, ab initio methods have been developed capable to test(More)
The UNEDF project was a large-scale collaborative effort that applied high-performance computing to the nuclear quantum many-body problem. UNEDF demonstrated that close associations among nuclear physicists, mathematicians, and computer scientists can lead to novel physics outcomes built on algorithmic innovations and computational developments. This review(More)
We report the microscopic origins of the anomalously suppressed beta decay of ¹⁴C to ¹⁴N using the ab initio no-core shell model with the Hamiltonian from the chiral effective field theory including three-nucleon force terms. The three-nucleon force induces unexpectedly large cancellations within the p shell between contributions to beta decay, which reduce(More)
High precision measurements of 26Na β− decay G. F. Grinyer,1,∗ C. E. Svensson,1 C. Andreoiu,1 A. N. Andreyev,2 R. A. E. Austin,3,† G. C. Ball,2 R. S. Chakrawarthy,2 P. Finlay,1 P. E. Garrett,1,2 G. Hackman,2 J. C. Hardy,4 B. Hyland,1 V. E. Iacob,4 K. A. Koopmans,3 W. D. Kulp,5 J. R. Leslie,6 J. A. Macdonald,2 A. C. Morton,2 W. E. Ormand,7 C. J. Osborne,2 C.(More)
Properties of finite nuclei are evaluated with two-nucleon (NN) and three-nucleon (NNN) interactions derived within chiral effective field theory. The nuclear Hamiltonian is fixed by properties of the A=2 system, except for two low-energy constants (LECs) that parametrize the short range NNN interaction, which we constrain with the A=3 binding energies. We(More)
We present a qualitative improvement of the ab initio no-core shell model (NCSM) approach by implementing three-body interaction capability for p-shell nuclei. We report the first calculations using three-body effective interactions derived from realistic nucleon-nucleon potentials for 6Li, 8Be, and 10B and demonstrate that the use of three-body effective(More)
We introduce a shell-model theory that combines traditional spherical states, which yield a diagonal representation of the usual single-particle interaction, with collective configurations that track deformations, and test the validity of this mixed-mode, oblique-basis shell-model scheme on Mg. The correct binding energy ~within 2% of the full-space result!(More)
The ground state band in (46)Cr and the isospin T = 1 band in (46)V have been delineated up to Ipi = 10(+) (tentatively 12(+)). These observations complete the highest spin T = 1 isospin triplet known. Following the isobaric multiplet mass equation, a combination of level energies in (46)Cr, (46)Ti, and (46)V are taken to highlight the angular momentum(More)