Abstract
The Coulomb energies of valence particles in Ne18 and Ti42 are calculated using realistic two-particle wave functions. The extra correlation in the configuration-mixed wave functions increases the Coulomb interaction by ∼150 keV for the 0+ state, and ∼50 keV for the 2+. This large effect brings the theoretical binding-energy differences of the mass-18 and mass-42 isospin triplets into agreement with experiment, but yields an average interaction larger than required by the binding-energy systematics of heavier nuclei.