Get the average charge density around each local minima in the charge density
        and store the result in _extrema_df
        Args:
            r (float): radius of sphere around each site to evaluate the average

def sort_sites_by_integrated_chg(self, r=0.4):
        """
        Get the average charge density around each local minima in the charge density
        and store the result in _extrema_df
        Args:
            r (float): radius of sphere around each site to evaluate the average
        """

        if self.extrema_type is None:
            self.get_local_extrema()
        int_den = []
        for isite in self.extrema_coords:
            mask = self._dist_mat(isite) < r
            vol_sphere = self.chgcar.structure.volume * (mask.sum()/self.chgcar.ngridpts)
            chg_in_sphere = np.sum(self.chgcar.data['total'] * mask) / mask.size / vol_sphere
            int_den.append(chg_in_sphere)
        self._extrema_df['avg_charge_den'] = int_den
        self._extrema_df.sort_values(by=['avg_charge_den'], inplace=True)
        self._extrema_df.reset_index(drop=True, inplace=True)