Increased demand for accurate values of isospin mixing has been stimulated by the recent high-precision measurements of superallowed -decay rates [6,7]. Large-scale shell-model approaches , although very accurate in the description of configuration mixing, can hardly account for the long-range polarization exerted on the neutron and proton states by the Coulomb force whose accurate treatment requires using large configuration spaces. In contrast, in self-consistent DFT, such polarization effects are naturally accounted for by finding the proper balance between the Coulomb force, which tends to make the proton and neutron states different, and the isoscalar part of the strong force, which has an opposite tendency.
In general, isospin impurities determined without removing spurious isospin mixing are underestimated by about 30% compared to the values obtained after rediagonalization . In the particular case of Zr, the removal of spurious admixtures increases from 2.9% to 4.4%, as illustrated in Fig. 1. It is encouraging to see that the latter value agrees well with the central value of empirical impurity deduced from the giant dipole resonance -decay studies, as communicated during this meeting by F. Camera et al. . Unfortunately, experimental error bars are too large to discriminate between various Skyrme parametrizations, which differ in predicted values of by as much as 10%.
Figure 2 illustrates our attempts to correlate the values of with the surface and volume symmetry energies, which are primary quantities characterizing the isovector parts of nuclear EDFs. The linear regression coefficients shown in the figure hardly indicate any correlation of with these quantities. In fact, no clear correlation was found between the calculated values of and other bulk characteristics of the Skyrme EDFs, including the isovector and isoscalar effective masses, and incompressibility.