code: def get_max_bond_distance(self, el1_sym, el2_sym):
          
          return sqrt(
              (self.el_radius[el1_sym] + self.el_radius[el2_sym] + self.tol) ** 2)
docs: Use Jmol algorithm to determine bond length from atomic parameters
          Args:
              el1_sym: (str) symbol of atom 1
              el2_sym: (str) symbol of atom 2
  
          Returns: (float) max bond length