def read_core_state_eigen(self):
        """
        Read the core state eigenenergies at each ionic step.

        Returns:
            A list of dict over the atom such as [{"AO":[core state eig]}].
            The core state eigenenergie list for each AO is over all ionic
            step.

        Example:
            The core state eigenenergie of the 2s AO of the 6th atom of the
            structure at the last ionic step is [5]["2s"][-1]
        """

        with zopen(self.filename, "rt") as foutcar:
            line = foutcar.readline()
            while line != "":
                line = foutcar.readline()
                if "NIONS =" in line:
                    natom = int(line.split("NIONS =")[1])
                    cl = [defaultdict(list) for i in range(natom)]
                if "the core state eigen" in line:
                    iat = -1
                    while line != "":
                        line = foutcar.readline()
                        # don't know number of lines to parse without knowing
                        # specific species, so stop parsing when we reach
                        # "E-fermi" instead
                        if "E-fermi" in line:
                            break
                        data = line.split()
                        # data will contain odd number of elements if it is
                        # the start of a new entry, or even number of elements
                        # if it continues the previous entry
                        if len(data) % 2 == 1:
                            iat += 1  # started parsing a new ion
                            data = data[1:]  # remove element with ion number
                        for i in range(0, len(data), 2):
                            cl[iat][data[i]].append(float(data[i + 1]))
        return cl
Read the core state eigenenergies at each ionic step.

        Returns:
            A list of dict over the atom such as [{"AO":[core state eig]}].
            The core state eigenenergie list for each AO is over all ionic
            step.

        Example:
            The core state eigenenergie of the 2s AO of the 6th atom of the
            structure at the last ionic step is [5]["2s"][-1]