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 th e framework of the relativistic mean-field (RMF) theory using the gene rator coordinate method (GCM). The constrained incompressibility and t he excitation energy of isoscalar giant monopole states are obtained f or finite nuclei with various sets of Lagrangian parameters. A compari son is made with the results of nonrelativistic constrained Skyrme Har tree-Fock (HF) calculations and with those from Skyrme random phase ap proximation (RPA) calculations. In the RMF theory the GCM calculations give a transition density for the breathing mode, which greatly resem bles that obtained from the Skyrme HF+RPA approach and also that from the scaling mode of the GMR. From the systematic study of the breathin g-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 th e empirical breathing-mode energies of heavy nuclei can be reproduced by forces with an incompressibility close to K = 300 MeV in the RMF th eory.