def METHOD_NAME(self, hdf, group_name="volumetric_data"):
    """
    Extract a VolumetricData instance from an HDF5 file.
    Args:
        hdf (pyiron_base.generic.hdfio.ProjectHDFio): The HDF
            file/path to read the data
        group_name (str): The name of the group under which
            the data have been stored
    Returns:
        pyiron.atomistics.volumetric.generic.VolumetricData: The
            VolumetricData instance
    """
    with hdf.open(group_name) as hdf_vd:
        self._total_data = hdf_vd["total"]
        if len(self._total_data) == 2:
            self.is_spin_polarized = True
        if "diff" in hdf_vd.list_nodes():
            self._diff_data = hdf_vd["diff"]