{
  "id": "1809.07571",
  "version": "v1",
  "published": "2018-09-20T11:11:33.000Z",
  "updated": "2018-09-20T11:11:33.000Z",
  "title": "Natural orbitals for ab initio no-core shell model calculations",
  "authors": [
    "Alexander Tichai",
    "Julius Müller",
    "Klaus Vobig",
    "Robert Roth"
  ],
  "comment": "7 pages, 7 figures",
  "categories": [
    "nucl-th"
  ],
  "abstract": "We explore the impact of optimizations of the single-particle basis on the convergence behavior and robustness of ab initio no-core shell model calculations. Our focus is on novel basis sets defined by the natural orbitals of a correlated one-body density matrix that is obtained in second-order many-body perturbation theory. Using a perturbatively improved density matrix as starting point informs the single-particle basis about the dominant correlation effects on the global structure of the many-body state, while keeping the computational cost for the basis optimization at a minimum. Already the comparison of the radial single-particle wavefunctions reveals the superiority of the natural-orbital basis compared to a Hartree-Fock or harmonic oscillator basis, and it highlights pathologies of the Hartree-Fock basis. We compare the model-space convergence of energies, root-mean-square radii, and selected electromagnetic observables with all three basis sets for selected p-shell nuclei using chiral interactions with explicit three-nucleon terms. In all cases the natural-orbital basis provides the fastest and most robust convergence, making it the most efficient basis for no-core shell model calculations. As an application we present no-core shell model calculations for the ground-state energies of all oxygen isotopes and assess the accuracy of the normal-ordered two-body approximation of the three-nucleon interaction in the natural-orbital basis.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-09-20T11:11:33.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "ab initio no-core shell model",
      "initio no-core shell model calculations",
      "natural orbitals",
      "natural-orbital basis"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 7,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}