The symmetry potential has the form

\[ U_{Sym} = \pm 2 S_{pot} \frac{\rho_n - \rho_p}{\rho_0} \,, \]

where \( \rho_n\) is neutron density and \( \rho_p\) is proton density. Definition and implementation are still to be worked out.

S_pot (double, required, no default):
Parameter \(S_{pot}\) of symmetry potential in MeV