def METHOD_NAME(self):
    spectrum_dict={}
    frequencies =[]
    for idx in range(self.exct):
        path_to_DG = os.path.join(self.output_dir, "{}_DynamicalGreen_{}.dat".format(header,idx))
        spectrum = np.loadtxt(path_to_DG)
        spectrum_dict[idx] = spectrum[:,2] + 1J*spectrum[:,3]
        if idx == 0 :
            frequencies = spectrum[:, 0] + 1J*spectrum[:, 1]
    self.spectrums_dict = spectrum_dict
    self.frequencies = frequencies
    return spectrum_dict