Perform Voronoi analysis on a list of Structures.
        Note that this might take a significant amount of time depending on the
        size and number of structures.

        Args:
            structures (list): list of Structures
            cutoff (float: cutoff distance around an atom to search for
                neighbors
            step_freq (int): perform analysis every step_freq steps
            qhull_options (str): options to pass to qhull
            most_frequent_polyhedra (int): this many unique polyhedra with
                highest frequences is stored.

        Returns:
            A list of tuples in the form (voronoi_index,frequency)

def analyze_structures(self, structures, step_freq=10,
                           most_frequent_polyhedra=15):
        """
        Perform Voronoi analysis on a list of Structures.
        Note that this might take a significant amount of time depending on the
        size and number of structures.

        Args:
            structures (list): list of Structures
            cutoff (float: cutoff distance around an atom to search for
                neighbors
            step_freq (int): perform analysis every step_freq steps
            qhull_options (str): options to pass to qhull
            most_frequent_polyhedra (int): this many unique polyhedra with
                highest frequences is stored.

        Returns:
            A list of tuples in the form (voronoi_index,frequency)
        """
        voro_dict = {}
        step = 0
        for structure in structures:
            step += 1
            if step % step_freq != 0:
                continue

            v = []
            for n in range(len(structure)):
                v.append(str(self.analyze(structure, n=n).view()))
            for voro in v:
                if voro in voro_dict:
                    voro_dict[voro] += 1
                else:
                    voro_dict[voro] = 1
        return sorted(voro_dict.items(),
                      key=lambda x: (x[1], x[0]),
                      reverse=True)[:most_frequent_polyhedra]