when an *ac* electric field perturbs the system. It has been proposed that the drifting/hopping of dipoles from one potential well to another causes relaxations . However, without distinguishing dipoles inside and outside the potential well, such proposal seems to have a tendency of confusing the wait time before hopping, $t$ (which reflects the distribution of dipoles at a given temperature) with the relaxation time, $\tau$ (which reflects how fast dipoles drift to the transient energy minimum and relates to the loss peak frequency in the Debye function), leading to some difficulties.

Limitations
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In previous studies [@Wang2014; @Wang2016; @PMNeffHami2015], *ab initio* calculation was used, which prescribes all important interactions between dipoles and other degrees of freedom in relaxors, and MC or MD was used to numerically work out the consequences. In the present work we do not start from *ab initio* calculation, instead, employs statistical and phenomenological arguments. Having shown results and insights obtained with this approach, we now discuss possible limitations to the present approach with respect to treatment of details, accuracy, and prediction power.

First, the proposed equations for lead-free [\[]{}Eq. (\[eq:BZT-frequency\])[\]]{} and lead-based relaxors [\[]{}Eq. (\[eq:PZN-1\])[\]]{} have five and seven parameters, respectively. Ideally, one hopes to 