Start by fitting a one-Kubo model and then add more components. For best performance with two or more components, avoid degeneracy by restricting the boundary conditions of each time component to a different time scale (e.g. 0.1 -2.0 ps and 1.0 -10 ps). Use the time constant from the one-Kubo component fit to estimate the dividing line between the two time scales with comfortable overlap to avoid over constraining. With the exception of null components, convergence will not occur for models having more Kubo components than truly present in the data. Note that it is practically impossible to resolve a Kubo correlation time much longer than the vibrational lifetime due to low SNR at longer T w , which is similarly true for the CLS method. 10. When exploring different models, VIFs are a useful tool for monitoring multicollinearity.