get the sum of several ICOHP values that are indicated by a list of labels (labels of the bonds are the same as in ICOHPLIST/ICOOPLIST)
        Args:
            label_list: list of labels of the ICOHPs/ICOOPs that should be summed
            divisor: is used to divide the sum
            summed_spin_channels: Boolean to indicate whether the ICOHPs/ICOOPs of both spin channels should be summed
            spin: if summed_spin_channels is equal to False, this spin indicates which spin channel should be returned

        Returns:
             float that is a sum of all ICOHPs/ICOOPs as indicated with label_list

def get_summed_icohp_by_label_list(self, label_list, divisor=1.0, summed_spin_channels=True, spin=Spin.up):
        """
        get the sum of several ICOHP values that are indicated by a list of labels (labels of the bonds are the same as in ICOHPLIST/ICOOPLIST)
        Args:
            label_list: list of labels of the ICOHPs/ICOOPs that should be summed
            divisor: is used to divide the sum
            summed_spin_channels: Boolean to indicate whether the ICOHPs/ICOOPs of both spin channels should be summed
            spin: if summed_spin_channels is equal to False, this spin indicates which spin channel should be returned

        Returns:
             float that is a sum of all ICOHPs/ICOOPs as indicated with label_list
        """
        sum_icohp = 0
        for label in label_list:
            icohp_here = self._icohplist[label]
            if icohp_here.num_bonds != 1:
                warnings.warn("One of the ICOHP values is an average over bonds. This is currently not considered.")
            # prints warning if num_bonds is not equal to 1
            if icohp_here._is_spin_polarized:
                if summed_spin_channels:
                    sum_icohp = sum_icohp + icohp_here.summed_icohp
                else:
                    sum_icohp = sum_icohp + icohp_here.icohpvalue(spin)
            else:
                sum_icohp = sum_icohp + icohp_here.icohpvalue(spin)
        return sum_icohp / divisor