code: def RB_to_OPLS(c0, c1, c2, c3, c4, c5):
      
  
      f1 = (-1.5 * c3) - (2 * c1)
      f2 = c0 + c1 + c3
      f3 = -0.5 * c3
      f4 = -0.25 * c4
      return np.array([f1, f2, f3, f4])
docs: Converts Ryckaert-Bellemans type dihedrals to OPLS type.
  
      Parameters
      ----------
      c0, c1, c2, c3, c4, c5 : Ryckaert-Belleman coefficients (in kcal/mol)
  
      Returns
      -------
      opls_coeffs : np.array, shape=(4,)
          Array containing the OPLS dihedrals coeffs f1, f2, f3, and f4
          (in kcal/mol)