Deviation from quadrupole-only predictions in fusion orientations due to hexadecapole deformation

This study re-examines the influence of quadrupole deformation β2 on optimum fusion orientations and, for the first time in this context, investigates the role of hexadecapole deformation β4 using a microscopic framework. Employing the Skyrme energy density formalism (SEDF) within the semiclassical extended Thomas–Fermi (ETF) approach, we analyse hot-compact and cold-elongated configurations in the fusion of silicon isotopes. While earlier studies based on phenomenological models, such as the Prox77 proximity potential, suggested that optimum orientations depend solely on the sign of β2 and are unaffected by higher-order deformations, our findings show otherwise. We demonstrate that β4 can induce significant deviations, up to 40◦ , in optimum hot-compact orientations. In contrast, cold-elongated configurations remain unchanged. Moreover, we find that optimum orientations depend on both the sign and the magnitude of β2, particularly when β2 is large. Our results reveal that higher-order multipole deformations are essential for a precise description of orientation-dependent fusion dynamics.