Center-of-mass problem in truncated configuration interaction and coupled-cluster calculations

TL;DR

This paper investigates the center-of-mass contamination issue in nuclear structure calculations using CI and CC methods, proposing a diagnostic scheme and comparing different truncation schemes for their CM contamination levels.

Contribution

It introduces a rigorous diagnostic method for CM contamination and compares the impact of various model space truncations on CM contamination in nuclear calculations.

Findings

CI and CC calculations show significant CM contamination with certain truncations.

The importance-truncated no-core shell model is nearly free of CM contamination.

The diagnostic scheme effectively quantifies CM contamination in intrinsic observables.

Abstract

The problem of center-of-mass (CM) contaminations in ab initio nuclear structure calculations using configuration interaction (CI) and coupled-cluster (CC) approaches is analyzed. A rigorous and quantitative scheme for diagnosing the CM contamination of intrinsic observables is proposed and applied to ground-state calculations for He-4 and O-16. The CI and CC calculations for O-16 based on model spaces defined via a truncation of the single-particle basis lead to sizable CM contaminations, while the importance-truncated no-core shell model based on the $N_{\max}\hbar\Omega$ space is virtually free of CM contaminations.