Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; China Inst Atom Energy, Beijing 102413, Peoples R China
; China Ctr Adv Sci & Technol, World Lab, Beijing 100080, Peoples R China
; Natl Lab Heavy Ion Accelerator Lanzhou, Ctr Theoret Nucl Phys, Lanzhou 730000, Peoples R China
; Chinese Acad Sci, Inst Theoret Phys, Beijing 100080, Peoples R China
The contribution of the resonant continuum to pairing correlations is properly treated in the RMF + BCS approximation with a constant pairing strength. The results show that the contribution of the proper treatment of the resonant continuum to pairing correlations for those nuclei close to neutron drip line is important. The quasiparticle relativistic random phase approximation is applied to investigate the collective excitations of the open shell nucleus. The numerical calculations are performed in the case of various isoscalar giant resonances of nucleus Sn-120. The calculated results show that the quasiparticle relativistic random phase approximation approach could satisfactorily reproduce the experimental data of the energies of low-lying states.