Nuclear collective excitations using correlated realistic interactions: The role of explicit random-phase approximation correlations

Abstract

We examine to what extent correlated realistic nucleon-nucleon interactions, derived within the unitary correlation operator method (UCOM), can describe nuclear collective motion in the framework of first-order random-phase approximation (RPA). To this end we employ the correlated Argonne V18 interaction in calculations within the so-called ''Extended'' RPA (ERPA) and investigate the response of closed-shell nuclei. The ERPA is a renormalized RPA version which considers explicitly the depletion of the Fermi sea due to long-range correlations and thus allows us to examine how these affect the excitation spectra. It is found that the effect on the properties of giant resonances is rather small. Compared to the standard RPA, where excitations are built on top of the uncorrelated Hartree-Fock (HF) ground state, their centroid energies decrease by up to 1 MeV, approximately, in the isovector channel. The isoscalar response is less affected in general. Thus, the disagreement between our previous UCOM-based RPA calculations and the experimental data are to be attributed to other effects, namely to residual three-body terms in the Hamiltonian and to higher-order configurations. Single-particle energies and occupation probabilities obtained within the ERPA are compared with corresponding HF and perturbation-theory results and are discussed as well. The ERPA formalism ismore » presented in detail.« less