Returns:
            (dict): {hkl: area_hkl/total area on wulff}

def area_fraction_dict(self):
        """
        Returns:
            (dict): {hkl: area_hkl/total area on wulff}
        """
        return {hkl: self.miller_area_dict[hkl] / self.surface_area
                for hkl in self.miller_area_dict.keys()}