Nuclear asymmetry energy and isovector stiffness within the effective surface approximation

The isoscalar and isovector particle densities and the surface tension coefficients at the average binding energy are used to derive analytical expressions of the neutron skin thickness and the isovector stiffness of sharp edged proton-neutron asymmetric nuclei. For most Skyrme forces these quantities are significantly larger than the well known ones. Using the analytical isovector surface energy constants in the framework of the hydrodynamical and the Fermi-liquid droplet models the mean energies and the sum rules of the isovector giant dipole resonances are in fair agreement with the experimental data.