Gets the nuclear electric quadrupole moment in units of
        e*millibarns

        Args:
            isotope (str): the isotope to get the quadrupole moment for
                default is None, which gets the lowest mass isotope

def get_nmr_quadrupole_moment(self, isotope=None):
        """
        Gets the nuclear electric quadrupole moment in units of
        e*millibarns

        Args:
            isotope (str): the isotope to get the quadrupole moment for
                default is None, which gets the lowest mass isotope
        """

        quad_mom = self._el.nmr_quadrupole_moment

        if len(quad_mom) == 0:
            return 0.0

        if isotope is None:
            isotopes = list(quad_mom.keys())
            isotopes.sort(key=lambda x: int(x.split("-")[1]), reverse=False)
            return quad_mom.get(isotopes[0], 0.0)
        else:
            if isotope not in quad_mom:
                raise ValueError("No quadrupole moment for isotope {}".format(
                    isotope))
            return quad_mom.get(isotope, 0.0)