Predictions of nuclear charge radii*

In this study, we improve the relations of the charge-radius difference of two isotopes by considering a term that relates to the proton number and the parity of the neutron number. The correction reduces the root-mean-squared deviation to 0.0041 fm for 651 nuclei with a neutron number larger than 20, in comparison with experimental data compiled in the CR2013 database. The improved relations are combined with local relations consisting of the charge radii of four neighboring nuclei. These combinations also prove to be efficient in describing and predicting nuclear charge radii and can reflect the structure evolutions of nuclei. Our predictions of 2467 unknown nuclear charge radii at competitive accuracy, which are calculated using these two types of relations, are tabulated in the Supplemental Material.