Nucleon-pair approximation of the shell model: Unified formalism for both odd and even systems - art. no. 014304

The formalism for the nucleon-pair approximation of the shell model (NPSM) is greatly simplified by applying the Wick theorem for the coupled cluster in a more sagacious way. Using a new coupling scheme of the basis, the new formalism not only unifies the analytic expressions of the Hamiltonian matr ix elements for even and odd nuclei (odd-even or odd-odd), but more importa ntly reduces the computing time drastically, which is crucial for the NPSM calculations of odd nuclei to be realizable.