Minimum critical oxygen chemical potential along path.

        Args:
            min_voltage: The minimum allowable voltage for a given step
            max_voltage: The maximum allowable voltage allowable for a given
                step

        Returns:
            Minimum critical oxygen chemical of all compounds along the
            insertion path (a subset of the path can be chosen by the optional
            arguments).

def get_min_muO2(self, min_voltage=None, max_voltage=None):
        """
        Minimum critical oxygen chemical potential along path.

        Args:
            min_voltage: The minimum allowable voltage for a given step
            max_voltage: The maximum allowable voltage allowable for a given
                step

        Returns:
            Minimum critical oxygen chemical of all compounds along the
            insertion path (a subset of the path can be chosen by the optional
            arguments).
        """
        data = []
        for pair in self._select_in_voltage_range(min_voltage, max_voltage):
            if pair.muO2_discharge is not None:
                data.extend([d['chempot'] for d in pair.muO2_discharge])
            if pair.muO2_charge is not None:
                data.extend([d['chempot'] for d in pair.muO2_discharge])
        return min(data) if len(data) > 0 else None