Toward open-shell nuclei with coupled-cluster theory

Abstract

We develop a new method to describe properties of truly open-shell nuclei.\nThis method is based on single-reference coupled-cluster theory and the\nequation-of-motion method with extensions to nuclei with $A\\pm 2$ nucleons\noutside a closed shell. We perform proof-of-principle calculations for the\nground states of the helium isotopes $^{3-6}$He and the first excited $2^+$\nstate in $^6$He. The comparison with exact results from matrix diagonalization\nin small model spaces demonstrates the accuracy of the coupled-cluster methods.\nThree-particle--one-hole excitations of $^4$He play an important role for the\naccurate description of $^6$He. For the open-shell nucleus $^6$He, the\ncomputational cost of the method is comparable with the coupled-cluster\nsingles-and-doubles approximation while its accuracy is similar to\ncoupled-cluster with singles, doubles and triples excitations.\n