Import a .mat file with single potentials (a b m) into a pandas
    DataFrame

    Also export some variables of the MD struct into a separate structure

def _read_mat_mnu0(filename):
    """Import a .mat file with single potentials (a b m) into a pandas
    DataFrame

    Also export some variables of the MD struct into a separate structure
    """
    print('read_mag_single_file: {0}'.format(filename))

    mat = sio.loadmat(filename, squeeze_me=True)
    # check the version
    version = mat['MP']['Version'].item()
    if version != 'FZJ-EZ-2017':
        raise Exception(
            'This data format is not supported (expected: FZJ-EZ-2017)' +
            ' got: {}'.format(version)
        )

    df_emd = _extract_emd(mat, filename=filename)
    df_md = _extract_md(mat)

    return df_emd, df_md