Copy of all structures in the TransformedStructure. A
        structure is stored after every single transformation.

def structures(self):
        """
        Copy of all structures in the TransformedStructure. A
        structure is stored after every single transformation.
        """
        hstructs = [Structure.from_dict(s['input_structure'])
                    for s in self.history if 'input_structure' in s]
        return hstructs + [self.final_structure]