Furthermore, it should be exploited that the damped approach can be used at any frequency interval (including the X-ray regime), meaning that several batches of, e.g., four complex frequencies each, can be carried out simultaneously, thereby scanning a large frequency range in a (relatively) short amount of time. It is our experience that a cubic spline provides the best interpolation of the data points with respect to reproducing a broadened stick spectrum and avoiding an overfitting of the parameters.