The collective excitation phenomena in atomic nuclei are studied in twodifferent formulations of the Random Phase Approximation (RPA): (i) RPA basedon correlated realistic nucleon-nucleon interactions constructed within theUnitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA)derived from effective Lagrangians with density-dependent meson-exchangeinteractions. The former includes the dominant interaction-induced short-rangecentral and tensor correlations by means of an unitary transformation. It isshown that UCOM-RPA correlations induced by collective nuclear vibrationsrecover a part of the residual long-range correlations that are not explicitlyincluded in the UCOM Hartree-Fock ground state. Both RPA models are employed instudies of the isoscalar monopole resonance (ISGMR) in closed-shell nucleiacross the nuclide chart, with an emphasis on the sensitivity of its propertieson the constraints for the range of the UCOM correlation functions. Within theRelativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubovmodel, the occurrence of pronounced low-lying dipole excitations is predictedin nuclei towards the proton drip-line. From the analysis of the transitiondensities and the structure of the RQRPA amplitudes, it is shown that thesestates correspond to the proton pygmy dipole resonance.
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