Finally, we would like to emphasize the pitfalls of empirical fitting approaches, such as those often used in conjunction with the Cooper-Zare or l-mixing models. These models contain physical variables (transition-dipole matrix elements, phase shifts, etc.), which can be determined in one of two ways: via ab initio calculations or by treating them as adjustable parameters while fitting the model to experimental data. It is the latter approach that can be problematic, for given several empirical parameters it is usually possible to match the model to the experimental results, without guarantee that the "best" parameter values are physically meaningful. Ab initio calculations-such as ezDyson with correlated Dyson orbitals-do not always support the parameter values giving the best fit. Such discrepancies help one learn about essential physics of the problem-in the present case, the effect of the core dipole moment on the emitted photoelectrons.