Ryckaert-Bellmans potential in LAMMPS

Dear all, I plan to use GROMOS force field to simulate polymer in lammps. While “Ryckaert-Bellemans potential” is used to describe some dihedral types of polymer according to other literature. However, there seems to be no such function form in lammps. How could I handle it?

See: dihedral_style nharmonic command — LAMMPS documentation

Thanks for your reply!