By taking into account the surface diffuseness correction for unstable nuclei , the accuracy of the macroscopic-microscopic mass formula is further improved .
The rms deviation with respect to essentially all the available mass data falls to 298 keV , crossing the 0.3 MeV accuracy threshold for the first time within the mean-field framework .
Considering the surface effect of the symmetry potential which plays an important role in the evolution of the ” neutron skin ” toward the ” neutron halo ” of nuclei approaching the neutron drip line , we obtain an optimal value of the symmetry energy coefficient J = 30.16 MeV .
With an accuracy of 258 keV for all the available neutron separation energies and of 237 keV for the \alpha -decay Q-values of super-heavy nuclei , the proposed mass formula is particularly important not only for the reliable description of the r process of nucleosynthesis but also for the study of the synthesis of super-heavy nuclei .