Convergence in the no-core shell model with low-momentum two-nucleon interactions

TL;DR

This paper investigates how low-momentum two-nucleon interactions, evolved via renormalization group methods, improve convergence in no-core shell model calculations for light nuclei up to lithium-7, highlighting the systematic effects of cutoff variations.

Contribution

It demonstrates that using renormalization group evolved low-momentum interactions enhances convergence in NCSM calculations without additional transformations, with systematic cutoff dependence.

Findings

Significant convergence improvements at lower cutoffs.

Energy calculations satisfy the variational principle.

Cutoff dependence is systematic and comparable to initial potential errors.

Abstract

The convergence of no-core shell model (NCSM) calculations using renormalization group evolved low-momentum two-nucleon interactions is studied for light nuclei up to Li-7. Because no additional transformation was used in applying the NCSM framework, the energy calculations satisfy the variational principle for a given Hamiltonian. Dramatic improvements in convergence are found as the cutoffs are lowered. The renormalization group equations are truncated at two-body interactions, so the evolution is only approximately unitary and converged energies for A > 2 vary with the cutoff. This approximation is systematic, however, and for useful cutoff ranges the energy variation is comparable to natural-size truncation errors inherent from the initial chiral effective field theory potential.