Natural orbitals for many-body expansion methods

The nuclear many-body problem for medium-mass systems is commonly addressed using wave-function expansion methods that build upon a second-quantized representation of operators with respect to chosen computational basis. While various options the basis are available, perturbatively constructed natural orbitals recently have been shown lead significant improvement in applications yielding faster model-space convergence and lower sensitivity set parameters large-scale no-core shell model diagonalizations. This work provides detailed comparison single-particle sets systematic benchmark nonperturbative calculations in-medium similarity renormalization group approach. As key outcome we find construction large enables performing calculation reduced space much dimension, thus offering savings practice help extend reach ab initio towards heavier masses higher accuracy.