Impact of the surface energy coefficient on the deformation properties of atomic nuclei as predicted by Skyrme energy density functionals

Abstract

Background: In the framework of nuclear energy density functional (EDF) methods, many nuclear phenomena are related to the deformation of intrinsic states. Their accurate modeling relies on the correct description of the change of nuclear binding energy with deformation. The two most important contributions to the deformation energy have their origin in shell effects that are correlated to the spectrum of single-particle states, and the deformability of nuclear matter, that can be characterized by a model-dependent surface energy coefficient asurf.

Purpose: With the goal of improving the global performance of nuclear EDFs through the fine-tuning of their deformation properties, the purpose of this study is threefold. First, to analyze the impact of systematic variations of asurf on properties of nuclei; second, to identify observables that can be safely used to narrow down the range of appropriate values of asurf to be targeted in future parameter fits; third, to analyze the interdependence of asurf with other properties of a nuclear EDF.

Methods: Results for a large variety of relevant observables of deformed nuclei obtained from self-consistent mean-field calculations with a set of purpose-built SLy5sX parametrizations of the Skyrme EDF are correlated with the value of asurf.

Results: The performance of the SLy5sX parametrizations for characteristic energies of the fission barriers of 180Hg, 226Ra, and 240Pu, excitation energies, electromagnetic moments and moments of inertia of superdeformed states in the A≈190 region, properties of shape coexisting states at normal deformation in the Pb, Kr, and Zr region, properties of octupole-deformed 144Ba, even-even Th isotopes, and 110Zr, separation energies along isotopic and isotonic chains are compared with available experimental data.

Conclusions: The three main conclusions are that there is an evident preference for a comparatively low value of asurf, as expected from the performance of existing parametrizations; that the isospin dependence of the surface energy also needs further fine-tuning in order to describe trends across the chart of nuclei; and that a satisfying simultaneous description of fission barriers and superdeformed states requires a better description of the single-particle spectra.