Generator coordinate calculations for breathing-mode giant monopole resonance in the relativistic mean-field theory.

The breathing-mode giant monopole resonance (GMR) is studied within the framework of the relativistic mean-field theory (RMF) using the generator coordinate method (GCM). The constrained incompressibility and the excitation energy of isoscalar giant monopole states are obtained for finite nuclei with various sets of Lagrangian parameters. A comparison is made with the results of nonrelativistic constrained Skyrme Hartree-Fock (HF) calculations and with those from Skyrme random phase approximation (RPA) calculations. In the RMF theory the GCM calculations give a transition density for the breathing mode, which greatly resembles that obtained from the Skyrme HF+RPA approach and also that from the scaling mode of the GMA. From the systematic study of the breathing-mode as a function of the incompressibility in GCM, it is shown that the GCM succeeds in describing the GMR energies in nuclei and that the empirical breathing-mode energies of heavy nuclei can be reproduced by forces with an incompressibility close to K=300 MeV in the RMF theory.