def METHOD_NAME(self):
    energy_list = []
    with open(os.path.join(output_dir, "{}_energy.dat".format(header))) as f:
        lines = f.readlines()
        for line in lines:
            words = line.split()
            if len(words) != 0 and words[0] == "Energy":
                energy_list.append(float(words[1]))
    self.energy_list = energy_list
    self.ene_min = energy_list[0]
    self.ene_max = energy_list[len(energy_list)-1]
    for T in T_list:
        eta_ene = np.exp(-(self.ene_max-self.ene_min)/T)
        print("T = {}: exp[-beta(ene_max-ene_mix)] = {}".format(T, eta_ene))
        if eta_ene > eta:
            print("Warning: At T = {}, eta_ene is larger than eta.".format(T))
    return energy_list