RPA and ERPA with Correlated Realistic NN Interactions

The Unitary Correlation Operator Method (UCOM) provides a powerful scheme for carrying out ab initio nuclear structure calculations [1, 2, 3, 4]. In particular, it makes it possible to combine numerically affordable manybody Hilbert spaces with modern realistic NN interactions. Short-range correlations are explicitly taken into account. First results ranging from no-core shell model to HartreeFock (HF) and perturbation-theory calculations using correlated NN interactions have been reported previously. In this work we employ correlated interactions in RPA studies of nuclear response. Only natural-parity excitations of spherical, closed-shell nuclei have been considered so far. First, HF calculations of the nuclear ground state are performed. The RPA is self-consistently formulated in the HF single-particle basis (HF+RPA model). We have also used an extended RPA version [5] (ERPA), which is built on top of the true RPA ground state and involves an iterative solution of the RPA equations. The influence of groundstate correlations on excitation properties can then be assessed. Corrected single-particle energies and occupation numbers can also be obtained. We use the correlated interactions discussed in Ref. [4], based on the Argonne V18 potential. The results presented here were obtained in a harmonic-oscillator basis of 13 shells with the optimal value of the tensor correlation volume, I θ = 0.09 fm . Our RPA results on the isoscalar (IS) giant monopole resonance (ISGMR), for various medium and heavy nuclei, are in good agreement with the experimental data. An example is shown in Fig. 1, where we see also that the