code: def buckingham_input(self, structure, keywords, library=None,
                           uc=True, valence_dict=None):
          
          gin = self.keyword_line(*keywords)
          gin += self.structure_lines(structure, symm_flg=not uc)
          if not library:
              gin += self.buckingham_potential(structure, valence_dict)
          else:
              gin += self.library_line(library)
          return gin
docs: Gets a GULP input for an oxide structure and buckingham potential
          from library.
  
          Args:
              structure: pymatgen.core.structure.Structure
              keywords: GULP first line keywords.
              library (Default=None): File containing the species and potential.
              uc (Default=True): Unit Cell Flag.
              valence_dict: {El: valence}