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

gamma (double, no default):
Power \( \gamma \) in formula for \( S(\rho) \):

\[ S(\rho)=12.3\,\mathrm{MeV}\times (\frac{\rho}{\rho_0})^{2/3}+ 20\,\mathrm{MeV}\times(\frac{\rho}{\rho_0})^\gamma \]

Specify either this or S_pot. If gamma is specified, the factor S will depend on the baryon density. Otherwise it wil be constant.